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The stratigraphy and neotectonic significance of tsunami deposits beneath tidal marshes on Vancouver… Benson, Boyd E. 1996

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THE STRATIGRAPHY AND NEOTECTONIC SIGNIFICANCE OF TSUNAMI DEPOSITS BENEATH TIDAL MARSHES ON VANCOUVER ISLAND, BRITISH COLUMBIA by BOYD E. BENSON B.Sc, B.Sc.C.E., The University of Washington, 1992 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Earth and Ocean Sciences) We accept this thes\s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1996 © Boyd E. Benson, 1996 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the. head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada Date DE-6 (2/88) A B S T R A C T Two tsunami deposits in intertidal marshes on Vancouver Island, British Columbia, were studied to understand their stratigraphy, sedimentology and neotectonic significance. Tsunami sand sheets on Vancouver Island thin and fine landward, drape the marsh surface, contain marine microfossils, may be internally graded or stratified, and are similar in age and stratigraphic position to deposits of known earthquakes. These characteristics provide criteria for recognizing tsunami deposits in other areas. Historical accounts and 137rjs analysis indicate that the upper tsunami deposit is the product of the great Alaska earthquake in 1964. Radiocarbon ages of organic material associated with the lower deposit show that it was deposited after AD 1660. This deposit is attributed the most recent earthquake on the Cascadia subduction zone 300 yr ago. This study extends the known effects of Cascadia seismicity north of the Nootka fault zone, the northern boundary of the subducting Juan de Fuca plate. Two methods were used to decipher the neotectonic history at the northern end of the Cascadia subduction zone: (1) comparison of the two tsunami deposits; (2) alithofacies method, permitting comparison of land level change experienced by the older sand sheet on opposite sides of the Nootka fault zone since the earthquake about 300 yr ago. North of the Nootka fault zone, the older tsunami deposit becomes thinner and less continuous, whereas the 1964 tsunami deposit shows little change at the different sites. This contrast suggests that the 300-yr-old tsunami approached the study area from the south, and that the earthquake source that triggered it may have been south of the study area. A lithofacies method was developed to estimate coseismic and interseismic land level changes since that earthquake. This method involves comparison of the current elevation of the pre-earthquake surface with the elevation range of the lithofacies in which it was deposited. Between 0.2 and 1.6 m of coseismic subsidence and 1.1 m of post-seismic emergence occurred at a site south of the Nootka fault zone. Such coseismic subsidence and interseismic ii emergence is indicative of coseismic and interseismic deformation on a locked subduction zone. At two sites north of the Nootka fault zone there is no obvious stratigraphic evidence for coseismic land level change. Post-seismic submergence of 0.1 to 1.7 m is attributed mainly to eustatic sea level rise. The lack of coseismic subsidence and interseismic emergence at the northern sites suggests that subduction and earthquake rupture on the Cascadia subduction zone may not extend north of the Nootka fault zone. iii TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS iv LIST OF FIGURES vi LIST OF TABLES vii ACKNOWLEDGMENTS viii 1.0 INTRODUCTORY STATEMENTS 1 1.1 INTRODUCTION 1 1.2 STRUCTURE OF THESIS 3 2.0 TSUNAMI DEPOSITS BENEATH TIDAL MARSHES ON NORTHERN VANCOUVER ISLAND, BRITISH COLUMBIA 4 1.1 ABSTRACT 4 1.2 INTRODUCTION 5 1.3 SETTING 7 1.4 METHODS 8 1.5 STRATIGRAPHY AND SEDIMENTOLOGY 9 1.5.1 Fair Harbour 10 1.5.2 Neroutsos Inlet 17 1.5.3 Koprino Harbour 21 1.6 CHRONOLOGY 24 1.7 DISCUSSION 30 1.7.1 Origin of Sand Sheets 30 7.7.2 Age of Sand Sheets 32 1.7.3 Depositional Processes 33 1.7.4 Comparison of 1964 and 300-Yr-Old Tsunami 34 1.8 CONCLUSIONS 36 iv 3.0 MARSH LITHOFACIES ANALYSIS: IMPLICATIONS FOR RELATIVE SEA LEVEL RISE AND NEOTECTONIC TRENDS ON VANCOUVER ISLAND, BRITISH COLUMBIA 37 3.1 ABSTRACT 37 3.2 INTRODUCTION 38 3.3 SETTING 40 3.4 LITHOFACIES DESCRIPTIONS 44 3.4.1 Tidal Mud 44 3.4.2 Marsh Peat 44 3.4.3 Upland Soil 44 3.5 LITHOFACIES METHOD 46 3.6 RESULTS 46 3.4.1 Tofino 46 3.4.2 Fair Harbour and Koprino Harbour 49 3.7 DISCUSSION 49 3.5.1 Causes of Relative Sea Level Change 49 3.5.2 Accuracy of the Lithofacies Method 50 3.5.3 Tectonic Implications 51 3.8 CONCLUSIONS 51 4.0 CONCLUSIONS 53 4.1 SUMMARY 53 4.2 FUTURE WORK 54 REFERENCES 56 APPENDIX 1 FAIR HARBOUR DATA 61 APPENDIX 2 NEROUTSOS INLET DATA 87 APPENDIX 3 KOPRINO HARBOUR DATA 92 v L I S T O F F I G U R E S 2.1 Cascadia subduction zone and inset map 6 2.2A Fair Harbour marsh overview 11 2.2B Outcrop at Fair Harbour showing sand sheets 12 2.3A Fair Harbour air photo 13 2.3B Neroutsos Inlet air photo 14 2.3C Koprino Harbour air photo 15 2.4 Fair Harbour fence diagram 16 2.5 Particle size trends at Fair Harbour 18 2.6 Thickness trends at Fair Harbour 19 2.7 Sand sheet couplets in the lower sand sheet at Fair Harbour 20 2.8 Neroutsos Inlet fence diagram 22 2.9 Koprino Harbour fence diagram 23 2.10 Calibrated radiocarbon ages 26 2.11 137Csages 28 2.12 Characteristics of tsunami deposits 31 3.1 Cascadia subduction zone and inset map 39 3.2A Buried marsh soil and tsunami sand at Tofino 42 3.2B Peat and lower tsunami sand at Fair Harbour 43 3.3 Marsh lithofacies 45 3.4 Results of lithofacies analysis 47 vi LIST OF TABLES 2.1 Radiocarbon ages 25 2.1 1 3 7 C s results.... 29 3.1 Land level changes associated with the pre-earthquake surface 48 vii ACKNOWLEDGMENTS This thesis project was made possible through the helpful guidance, discussion, and encouragement from many individuals. I would like to thank my supervisory committee of Kurt Grimm, John Clague, and Michael Church for allowing me the latitude to research this thesis in a way that was intellectually stimulating and rewarding. They have inspired me to do my best with their constant support and encouragement, and have helped me to become a better scientist. Brian Atwater and Jody Bourgeois first introduced me to the wonders of working in mud in Cascadia, and have been very generous with their time and inspiration. The continual support of my family has made these last few years very enjoyable, and the role model provided by my Dad will always be a constant motivation to me (thanks for all of the soup!). Assistance in the field from Lorin Amidon and Craig Churchill strengthened this work, and made for an outstanding field season. I thank Ian Hutchinson for discussion and diatom identification, Roger McNeely for radiocarbon ages, Tark Hamilton for cesium analysis, and Natasha Lyons for help in the laboratory. Funding for this work was partially provided by the Natural Sciences and Engineering Research Council of Canada, the Geological Survey of Canada, and the Geological Society of America. viii CHAPTER 1 INTRODUCTORY STATEMENTS 1.1 INTRODUCTION There are no written accounts of earthquakes along the offshore boundary between the North America plate and the subducting Juan de Fuca and Gorda plates (Cascadia subduction zone, Fig. 2.1). The lack of historical seismicity has been attributed to aseismic creep, similar to that occurring at the Marianas subduction zone, or a locked plate boundary that is storing elastic strain to be released in a future earthquake, as is happening at subduction zones off Chile and Alaska (Heaton and Hartzell, 1986). Geophysical models and geodetic measurements (Heaton and Hartzell, 1987; Rogers, 1988; Savage et al., 1991; Hyndman and Wang, 1993, 1995; Dragert et al., 1994) suggest that strain accumulating on this 1000-km-long plate boundary may be released either in a series of great, magnitude-8 earthquakes or a single giant, magnitude-9 earthquake. In the late 1980s and early 1990s researchers identified three types of geologic evidence in coastal wetlands that are best explained by seismicity on the Cascadia subduction zone: 1. Buried soils that were submerged abruptly, consistent with coseismic subsidence (Darienzo and Peterson, 1990; Atwater and Yamaguchi, 1991; Atwater, 1992; Clarke and Carver, 1992; Nelson, 1992; Clague and Bobrowsky, 1994a). 2. Sand sheets overlying buried soils; these sand sheets thin and fine landward, contain marine microfossils, and have been interpreted to be tsunami deposits (Atwater, 1987; Reinhart and Bourgeois, 1989; Clague and Bobrowsky, 1994b). 3. Intruded and extruded sand bodies, including clastic dikes and sand blows, 1 produced by liquefaction resulting from intense ground shaking (Obermeier et al., 1993; Atwater, 1994; Obermeier, 1995). Intervals between successive earthquakes range from a few centuries to perhaps more than 1000 years (Atwater et al., 1995; Atwater and Hemphill-Haley, 1996). Radiocarbon ages on herbaceous plants and trees in growth position that were submerged and subsequently buried date the most recent earthquake or series of earthquakes on the Cascadia subduction zone to between A.D. 1700 and 1720 (Nelson et al., 1995). Tree-ring dating of earthquake-stressed and -killed trees (Yamaguchi et al., 1989; Atwater and Yamaguchi, 1991; Benson et al., 1992) further supports this age assignment. Japanese historical records describing a large, unexplained tsunami may precisely date the most recent Cascadia earthquake to January 26, 1700 (Satake et al., 1996). While the buried soils and tsunami deposits are not precisely dated, they are strong evidence for a previously unrecognized hazard facing the Pacific Northwest. Two tsunami deposits in peat sequences at tidal marshes on northern Vancouver Island were studied to understand their stratigraphy, sedimentology, and neotectonic significance. This study identifies criteria useful in recognizing tsunami deposits in Cascadia and elsewhere. The deposits are similar in age, stratigraphic position, and morphology to tsunami deposits farther south that have been attributed to the 1964 Alaska earthquake and to the last great earthquake on the Cascadia subduction zone about 300 yr ago. This work extends the known record of the 300-yr-old Cascadia earthquake to an unstudied region north of the Nootka fault zone, the northern boundary of the subducting Juan de Fuca plate. Comparison of the thickness and continuity of the 1964 and 300-yr-old tsunami deposits provides constraints on the source of the 300-yr-old tsunami. These comparisons suggest that this tsunami was generated by an earthquake south of the Nootka fault zone as opposed to a source directly off-shore. A lithofacies method was used to estimate relative sea level change and to determine tectonically-induced land level changes on Vancouver Island. Comparisons of the 2 magnitude and direction of relative sea level change at three study sites suggest that there are fundamental differences in the tectonic environment north and south of the Nootka fault zone. 1.2 STRUCTURE OF THESIS This thesis was prepared as two independent journal-style articles. Because of topical similarity, there is some repetition of content. Chapter 2 describes the stratigraphy, age, identifying characteristics, and neotectonic significance of tsunami deposits at three sites on northern Vancouver Island. This chapter, titled 'Tsunami deposits beneath tidal marshes on northern Vancouver Island, British Columbia' was submitted to Quaternary Research in September 1996, and is co-authored by Kurt A. Grimm and John J. Clague. Chapter 3 describes a lithofacies method that is useful in determining relative sea level change on Vancouver Island. Using this method coseismic and interseismic land level change was estimated at marshes found on opposite sides of the Nootka fault zone. The results of this analysis are used to clarify the tectonic environment of Vancouver Island. This chapter, titled 'Marsh lithofacies analysis: Implications for relative sea level trends and neotectonics on Vancouver Island, British Columbia' will be submitted to Geology, and is co-authored by John J. Clague and Kurt A. Grimm. 3 C H A P T E R 2 T S U N A M I D E P O S I T S B E N E A T H T I D A L M A R S H E S O N N O R T H E R N V A N C O U V E R I S L A N D , B R I T I S H C O L U M B I A 2.1 A B S T R A C T Sand sheets at three tidal marshes record two tsunamis on the northwestern coast of Vancouver Island, British Columbia. ^Cs dating and historical accounts indicate that the upper sand sheet was deposited by the great Alaska earthquake in 1964. Radiocarbon ages on plant fossils within and on top of the lower sand sheet show that it was deposited sometime after A.D. 1660. We attribute the lower sand sheet to the tsunami of the most recent plate-boundary earthquake on the Cascadia subduction zone about 300 yr ago, extending the known effects of this earthquake north of the Nootka fault zone. Within the study area, the lower sand sheet becomes thinner and less continuous to the north, implying a tsunami source to the south. This suggests to us that the 300-yr-old rupture may not have extended north of the Nootka fault zone. In contrast, the 1964 tsunami deposit differs little in thickness and continuity among the three marshes. Our study has identified characteristics that aid in identifying tsunami deposits. Deposits of tsunamis are commonly landward-thinning and landward-fining sand sheets that drape the land surface, contain marine microfossils, may be graded or internally stratified, and are similar in age and stratigraphic position to deposits of known earthquakes. 4 2.2 INTRODUCTION There are no written accounts of earthquakes along the offshore boundary between the North America plate and subducting Juan de Fuca and Gorda plates (Cascadia subduction zone, Fig. 2.1). The lack of historical seismicity has been attributed to aseismic creep, similar to that occurring at the Marianas subduction zone, or a locked plate boundary that is storing elastic strain to be released in a future earthquake, as is happening at subduction zones off Chile and Alaska (Heaton and Hartzell, 1986). Geophysical models and geodetic measurements (Heaton and Hartzell, 1987; Rogers, 1988; Savage et al., 1991; Hyndman and Wang, 1993, 1995; Dragert et al., 1994) suggest that strain accumulating on this 1000-km-long plate boundary may be released either in a series of great, magnitude-8 earthquakes or a single giant, magnitude-9 earthquake. In the late 1980s and early 1990s researchers identified three types of geologic evidence in coastal wetlands that are best explained by seismicity on the Cascadia subduction zone (Atwater et al., 1995, and references therein): (1) buried soils that were submerged suddenly, consistent with coseismic subsidence; (2) sand sheets, interpreted to be tsunami deposits, which overlie buried soils, thin and fine landward, and contain marine microfossils; (3) intruded and extruded sand bodies, including clastic dikes and sand blows, produced by liquefaction resulting from intense ground shaking. Studies of this geologic evidence have shown that intervals between successive earthquakes range from a few centuries or less to perhaps more than 1000 yr (Atwater et al., 1995; Atwater and Hemphill-Haley, 1996). The most recent earthquake or series of earthquakes occurred between A.D. 1700 and 1720 (Atwater and Yamaguchi, 1991; Nelson et al., 1995), perhaps in January 1700 (Satake et al., 1996). While the buried soils and tsunami deposits are not precisely dated, they are strong evidence for a previously unrecognized hazard facing the Pacific Northwest. The purpose of this paper is to characterize tsunami deposits in Holocene peat at tidal marshes on northern Vancouver Island, British Columbia. We studied the 5 Figure 2.1. Map of the study area. Solid circles are study sites. Inset map shows lithospheric plates and the seaward edge of the Cascadia subduction zone. 6 architecture, stratigraphy, and sedimentology of two sand sheets at Fair Harbour, Neroutsos Inlet, and Koprino Harbour (Fig. 2.1) to understand their deposition, preservation, and paleoseismic significance, and to seek criteria for identifying tsunami deposits. The two sand sheets are similar in age, stratigraphic position, and morphology to tsunami deposits farther south that have been attributed to the 1964 Alaska earthquake and to the last great earthquake on the Cascadia subduction zone about 300 yr ago. Our findings extend the known paleoseismic record of the most recent great Cascadia earthquake to a previously unstudied region north of the Nootka fault zone, the northern boundary of the Juan de Fuca plate. Spatial variations in the thickness and continuity of the older sand sheet suggest that this tsunami was generated by an earthquake south of the Nootka fault zone. 2.3 SETTING Tidal marshes at Fair Harbour, Neroutsos Inlet, and Koprino Harbour were chosen for study because they are north of the Juan de Fuca plate, beyond the area previously shown to have been affected by earthquakes on the Cascadia subduction zone. The marshes at these three sites are large and are underlain by about 1 m of peat containing two anomalous sand sheets. The peat is underlain by Pleistocene glaciomarine clayey silt or by younger sand and gravel deposits similar to those found elsewhere on the coast of Vancouver Island (Friele and Hutchinson, 1993; Clague and Bobrowsky, 1994a). The sand and gravel may have been deposited during a transgression about 6000 to 7000 yr ago and then reworked during a late Holocene regression. The marshes, characterized by salt-tolerant plants, are situated within the upper half of the intertidal zone between unvegetated tidal flats and supratidal grass and forest. The mean tide range at the three study sites is about 2.9 m, and the maximum range is 4.5 m (Fisheries and Oceans, 1995). The present plate setting of northern Vancouver Island is not well understood. The 7 Nootka fault zone (Fig. 2.1), south of the study area, may mark the northern limit of the Cascadia subduction zone (Rohr and Furlong, 1995). The small Explorer plate, which is separated from the Juan de Fuca plate by the Nootka fault, is probably a broad deformational zone where convergence on the Cascadia subduction zone to the south changes into strike -slip motion along the North America-Pacific plate boundary to the north (Rohr and Furlong, 1995). The subducting Juan de Fuca plate, south of the Nootka fault, is locked against the overriding North America plate (Dragert et al., 1994; Hyndman and Wang, 1995). Evidence for locking and for the buildup of strain at the plate boundary includes geodetic measurements that reveal uplift and crustal shortening along the coast (Savage et al., 1991; Dragert et al., 1994). 2.4 METHODS We studied sediments at three tidal marshes in channel-bank outcrops, pits, and cores. Gridded transects with data points 5 m apart were installed by tape and Brunton compass in areas of minimal fluvial influence. The elevation of each grid point, relative to a temporary benchmark, was measured with an automatic leveling instrument or a hand level. Benchmarks were linked to high tide levels which were determined from regional tide gauge data corrected for local differences in time and magnitude (Fisheries and Oceans, 1995). Depths of contacts and sediment types, colors, and textures were recorded at each grid point from solid 1-m-long cores retrieved with a 2.5-cm-diameter gouge corer. Stratigraphic cross-sections and three-dimensional fence diagrams were constructed from these data. Monoliths of the sand sheets and enclosing peat were collected to study the sedimentology, internal stratigraphy, and microfossil assemblages of the deposits in the laboratory. Samples of sand were collected from the two sand sheets at each grid point at the Fair Harbour marsh for grain-size analysis. Particle-size distributions were determined with a 8 semi-automatic visual settling tube (Inter-Agency Committee on Water Resources, 1958). Fossil plant material, including sticks, conifer cones, bark, and leaf bases of in situ herbaceous plants, was retrieved from near and within the lower sand sheet and at the base of the peat sequence for radiocarbon dating. Eight samples were radiocarbon dated at IsoTrace Laboratory, the Geological Survey of Canada Radiocarbon Laboratory, and the Quaternary Isotope Laboratory of the University of Washington. Calendric ages were calculated from the radiocarbon ages using the decadal tree-ring dataset of Stuiver and Becker (1993). Ten samples from the upper 24 cm of the peat sequence at Fair Harbour were analyzed for 137rjs using an x-ray spectrometer at the Pacific Geoscience Centre (Geological Survey of Canada). The samples provide continuous coverage from the marsh surface to a depth of 12 cm below the upper sand. 2.5 STRATIGRAPHY AND SEDIMENTOLOGY Two thin, stratigraphically unique sand sheets occur in similar peat sequences at the Fair Harbour, Neroutsos Inlet, and Koprino Harbour marshes. The sand sheets are similar to seismogenic tsunami deposits at Port Alberni and Tofino farther south on Vancouver Island, described by Clague and Bobrowsky (1994b). Field work demonstrates that both sand sheets at each marsh thin and fine landward and blanket paleosurfaces with relief like that of the present-day marshes. Each sheet is commonly no more than 2 cm thick and consists of moderately sorted, very fine to very coarse sand and silt, composed of quartz, feldspar, and lithic fragments. The sands also contain sticks, cones, bark, rare shell fragments, foraminifera, and diatoms. The sand sheets are similar in texture and composition to adjacent tidal channel sediments. The sand sheets range from massive, to normally graded, to internally stratified. Locally, they consist of two or three couplets of sand and mud. Each sand-mud couplet 9 comprises a normally graded, sharply based, fine to coarse sand abruptly overlain by sandy mud. The couplets are best explained as deposits of multiple waves of a tsunami wave train (see Discussion). We found no obvious stratigraphic evidence for a change in land level at or about the time of deposition of the lower sand sheet. Diatoms in the peat directly above and below the lower sand sheet at Fair Harbour indicate a middle marsh environment (Ian Hutchinson, written communication, 1996). However, the sand itself contains marine diatoms that are absent on the modern marsh, including Navicula marina (Ian Hutchinson, written communication, 1996). The presence of marine diatoms indicates landward transport of the sand from the sea. 2.5.1 Fair Harbour Fair Harbour, the southernmost of the three study sites, is located 30 km north of the Nootka fault zone. The 30 ha marsh at the east end of Fair Harbour (Figs. 2.2A and 2.3A) is protected from the open ocean, 20 km away, by numerous islands and a narrow inlet. The tsunami triggered by the great Alaska earthquake of March 28, 1964 destroyed two bridges that crossed the marsh and moved buildings at a nearby logging camp (Glen Griffiths, B.C. Ministry of Forests, personal communication, 1995). We made 215 borings in a 50 m by 90 m grid in the tidally dominated, southeast part of the marsh, far from fluvial influences to the north and open water to the west (Figs. 2.2A and 2.3A). The marsh in this area is underlain by about 1 m of peat that contains the sand sheets (Fig. 2.4). The peat is uniform in texture and color to within 20 cm of its base, where it gradually grades down into a peaty mud; the peaty mud, in turn, overlies up to 3 m of sand and gravel (Fig. 2.2B). The sand and gravel overlie a thick sequence of clayey silt (AGRA Earth and Environment, 1993), probably a glaciomarine deposit. The two sand sheets thin and fine landward and away from tidal channels. Fair Harbour transect M L (Fig. 2.4) is interrupted by two 15-m-wide tidal channels. Sediment is 10 Figure 2.2A. Fair Harbour marsh; the study area is in the foreground. Arrows point to bridges rebuilt after their destruction by the 1964 Alaska tsunami. 11 Figure 2.2B. Bank of tidal channel at Fair Harbour; arrows indicate lower sand sheet; asterisk marks flagging on nail emplaced in the upper sand. Scale = 30 cm. 12 3 u c/l X i n ON i n o r-u pq o o X & c3 o g ^ O S U T 3 X no 1/3 *4-l o o X 03 H i 3 PQ u 3 '> O W> <N « a 3 X o 3 5 3 T 3 9 3 E 3 c3 O 3 as < -X T t u ^ Si 3 -3 X 1— ^ * • 3 O < o i B2 -a 3 '53 x 3 13 1 .2 CO XJ "2 6 o U u -gj CO |_ T 3 PQ s ^ CO & .5 3 o H • & i n 55 g •S ™ o J2 •3 < •S ^ _ ^ 3 ON 3 2 ? 2 OJ CO H u 2 -d o > *•> •*-> CO -2 6 cd 4-* I o "3 « i — i « co 'co O CO 3 o >-z PQ g 5o •»—i PH •±3 m £ 2! c £ to 00 ' u pa o o - xs I f 1 4 15 16 coarsest adjacent to both channels and fines away from them (Fig. 2.5). The sand sheets also thin inland away from these channels and pinch out near the forest edge (Fig. 2.6). Similar trends were seen elsewhere at Fair Harbour and in outcrops at Neroutsos Inlet and Koprino Harbour. The lower sand sheet consists of fine to very coarse sand; some gravel is present near the banks of tidal channels facing open water. The sand sheet averages 1.5 to 2.5 cm in thickness, but is locally up to 10 cm thick. It is commonly 60 to 70 cm below the marsh surface. Though typically massive or normally graded, the lower sand sheet locally comprises up to three couplets of basal clean fine to coarse sand overlain by muddy fine sand and silt (Fig. 2.7). Sticks, conifer cones, and bark are common in the sand. Leaf bases of marsh plants that had been growing prior to sand sheet deposition are entombed in the sand. The lower sand sheet rises 1.4 m from the open marsh to the forest edge. The upper sand sheet is composed of fine to medium sand. It averages 0.5 to 1 cm thick, has a maximum thickness of 2 cm, and is commonly 6 to 10 cm below the marsh surface. This sand sheet is generally massive, but in some places it consists of up to three couplets of coarse to fine sand and mud. 2.5.2 Neroutsos Inlet Neroutsos Inlet is a 2.5-km-wide fjord which branches off Quatsino Sound and penetrates 30 km south into the mountainous interior of northern Vancouver Island (Fig. 2.1). A 17 ha marsh at the head of the inlet (Fig. 2.3B) is protected from the open ocean by approximately 50 km of narrow waterways and by islands. According to Fred Lind, a veteran tug boat captain, log booms in the inlet and a hunting cabin at the head of the inlet (Fig. 2.3B) were destroyed by the 1964 Alaska tsunami (personal communication, 1995). Jetsam from the cabin was found suspended in tree branches 1.5 m above the ground, and a small wood stove was carried 20 m into the forest by the tsunami (Lou Walker, personal communication, 1995). 17 o CD CO c 03 i_ r -O O o CO o CD O o CM UBLjJ J9SJBO0 lUGOJed o CD CO c crj O C D TD c CO " D C C CO y= CO >> CD CO CD T J C CO CO T J CD > LL c CO CO E CD CO CO CD O CO ° co CT O CD o > f HI s o O CN cu IH 3 6 0 • E 8 oj b u o cn uo a a CJ <D OJ 3 co R 5 =3 2 u . 3 CO 3 o l-l rt H rt OJ 4= o 6 0 O O & OJ o rt +^ OJ OJ -a e cd CO CO rt OJ 3 3 OJ « rt ,g *= 1 ch OJ <4-H CO OJ 3 A 3 " M M OJ Hl oj rt l - l CO UBLII J 9 S J B O 0 l u e o j e d 18 CD D) "O CD CO L CD CD C c 03 x: O L i n r O -1—• CD CD SZ 00 T 3 •4—1 C CO CO CD CO CL o CO CD D) "D CD 00 CD E o >_ H— CD O c CTJ -t—' CO b 3 0 1 X S-. u. bO 3 _o 03 <U CD -C cn cfl U -o a j C M OH 3 OJ u 3 U EB 3 OJ l-c 3 1 3 U > o E c 3 U U j5 Cfl 03 <U -3 & IH BO O Q , O H 3 O 03 O O CN 3 u u u •a u Cfl - 3 o 3 -3 U "3 -a O - 3 VC3 O >^ IS) 3 u -3 cfl X ) Lfl OJ -3 H LO CD CD c c CO O 19 Figure 2.7. Couplets in the lower sand sheet at Fair Harbour. Each couplet is composed of a coarse basal layer and an overlying finer layer; the two coarse basal layers in this sample are bracketed by pins. Each couplet may record a separate surge of water in a tsunami wave train. 2 0 A 30 m by 30 m grid was established in the tidally dominated northeast portion of the marsh, away from fluvial influences to the west (Figs. 2.3B and 2.8). At the grid site the marsh is underlain by 0.8 m of peat which is uniform in texture and color to within 20 cm of its base, where it gradually grades downward into peaty mud. The peaty mud abruptly overlies at least 2 m of cobble gravel which is exposed in the banks of tidal channels. Two sand sheets are present throughout the grid site, but they occur only sporadically within thinner peat near the back of the marsh to the southeast. The lower sand sheet at the grid site is 1 to 2 cm thick, consists of medium to very coarse sand, and lies 40 to 60 cm below the marsh surface (Fig. 2.8). There are abundant leaf bases of the marsh plant Triglochin maritimum in the sand. The sand generally is massive, but locally is normally graded. The upper sand sheet at the grid site is 0.5 to 2 cm thick, is composed of very fine to coarse massive sand, and lies 4 to 12 cm below the marsh surface. In the forest, near the site of the cabin that was destroyed by the 1964 tsunami, stratified coarse sand and granules up to 17 cm thick underlie 2 cm of forest duff. This sediment probably correlates with the upper sand sheet at the grid site. 2.5.3 Koprino Harbour Koprino Harbour is located on the north side of Quatsino Sound about 50 km from the north end of Vancouver Island and 15 km from the open Pacific Ocean (Fig. 2.1). A 10 ha tidal marsh is protected by a small island within the harbour and by a large fan-delta that almost isolates the marsh from the open water of Quatsino Sound (Fig. 2.3C). A small tidal channel runs the length of the marsh. Boats and dock facilities at Winter Harbour, 10 km to the northwest, were damaged by the 1964 Alaska tsunami (Fred Lind, personal communication, 1995). We studied cores and outcrops along a 330-m-long axial transect in the eastern part of the marsh (Figs. 2.3C and 2.9). Seven shorter transects extend from forest edge to forest 21 22 *t OJ o 23 edge perpendicular to the axial transect. A 60- to 70-cm-thick peat unit containing two sand sheets (Fig. 2.9) is uniform in texture and color to within about 10 cm of its base, where it grades into peaty mud. These sediments overlie less than 20 cm of gravelly sand, which in turn overlies clayey silt containing bivalve shells. Both sand sheets thin and fine away from open water and the axial tidal channel. The lower sand sheet is continuous only within about 15 m of the axial tidal channel (Fig. 2.9), along which it rises 10 cm towards the forest. It is composed of fine to very coarse sand, is 0.1 to 1 cm thick, and commonly lies 60 to 70 cm below the marsh surface. Possibly correlative, discontinuous lenses of sand up to 12 cm thick are present near the forest edge. The upper sand sheet rises 0.4 m away from the tidal channel towards the forest, but only locally reaches it. It is composed of fine sand, is 0.5 cm thick on average, and lies 5 to 8 cm below the marsh surface. 2.6 CHRONOLOGY Clayey silt at the base of the succession at Koprino Harbour and in boreholes at Fair Harbour is probably correlative with similar late Pleistocene glaciomarine sediments at Tofino and Ucluelet to the south (Friele and Hutchinson, 1993; Clague and Bobrowsky, 1994a). Bivalve shells collected from the Tofino sediments yielded a radiocarbon age of 13,780 ± 110 1 4 C yr B.P. (TO-2365; Clague and Bobrowsky, 1994a). A stick from the base of the peat at Fair Harbour gave ages of 290 ± 80 and 300 ± 80 14c yr B.P., indicating that peat accumulation began there less than 550 cal yr ago (Table 2.1). Sand and gravel below the peat are probably a lag that spans much of Holocene time (Clague and Bobrowsky, 1994a). 24 S T d 3 o X c j CD o s o cn O DH X U H bO Q is X SH r H o H-l 3 3 CN CD bO <H , V cD X bO U * < c j in T d > ^ 3 w "3 u CD bo ^ OQ U • 7 3 —I c j w 3 o c j CD o PH T d c l >H (U o CD > o o o vo oo C N i T d cn CD O CD > O •8 a o ^ ^ H CD O CO 00 T d s c j cn I n CD O 3 O > 3 CD bO c j , I H Cj PQ T3 3 c j cn T d wer 3 3 wer c j c j wer on cn T d o S-H 3 CD CD c j 3 cn O O wer CD wer 3 _ B _s wer O o O cn cn C3 1) cn CD cn CCS c j o X X "53 4-H a. 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CD CD ^ O 3 U ^ 00 DH is ^ 2 1 o 5 / 5 x o c j X 3 CD "3 CD CD bO u >o r-C N — ; 00 V O C N C N C N i i i II II II u u u r2 cn cn cn cn <D oo bO ^ T d C N <D 1 ts II X U X cn Cj -H U C O - H C N O 3 C l K l IO C O C O C O O O 0\ 25 to CL Q 1964( 1 3 7Cs) 1 (D <D- -Late Pleistocene I L J I L I I I L J I 1300 1400 1500 1600 1700 1800 1900 r—] p e a t Calibrated age (yr A.D.) Sand sheet • Sand and gravel • Glaciomarine mud Q Radiocarbon sample, Table 1 Figure 2.10. Plot of radiocarbon ages of dated plant material. The stratigraphic section is generalized from observations at the three studied marshes. Horizontal lines are two standard deviation ranges calculated with an error multiplier of 2 (dataset of Stuiver and Becker, 1993). The vertical bar represents the probable age range of the most recent plate boundary earthquake(s) at the Cascadia subduction zone (Nelson et al., 1995). 26 The age of the lower sand sheet is further constrained by six additional radiocarbon ages (Table 2.1, Fig. 2.10). Leaf bases of Triglochin maritimum, which are rooted in the peat and were buried when the sand was deposited, yielded radiocarbon ages of 40 ±50 yr B.P. at Koprino Harbour and 160 1 4 C yr B.P. at Neroutsos Inlet. A stick 2-3 cm below the lower sand at Fair Harbour yielded an age of 270 ± 80 yr B.P. Part of a hemlock cone lying on the lower sand at this locality gave an age of 60 ± 50 yr B.P.; a stick at the same level was dated at 6930 ± 80 1 4 C yr B.P. A piece of bark resting on the lower sand at Neroutsos Inlet gave an age of 230 ± 50 1 4 C yr B.P. Radiocarbon ages on herbaceous plants that were living on the marsh at the time of sand deposition most closely date the tsunami. The two dates on Triglochin leaf bases correspond to calendric ages younger than A.D. 1659. Radiocarbon ages on sticks, bark, and other detrital material associated with the sand sheet provide only maximum dates for the tsunami. The youngest of the ages on detritus (60 ± 50 1 4C yr B.P.) corresponds to calendric ages more recent than A.D. 1653 and is compatible with the Triglochin ages. The stick dated at 6930 ± 80 * 4 C yr B.P. is much older than the enclosing sediment and must have been recycled from an older deposit. Peat just below the upper sand sheet at Fair Harbour has a high concentration of 137 C s (Fig. 2.11, Table 2.2), related to atmospheric nuclear testing which began in 1953 and peaked around 1964 (Clague et al., 1994). The cesium data show that the upper sand sheet dates to the late 1950s or early 1960s, and supports the conclusion that this sand was deposited by the 1964 Alaska tsunami (see Discussion). 27 Figure 2.11. Cesium activity (pCi/g) in the upper part of the peat at Fair Harbour. The increase in J 'Cs activity between 15 and 12 cm marks a major increase in atmospheric nuclear testing in the early 1950s; the peak in testing and 1 3 7 Cs activity occurred around 1964. The rectangles represent samples used for 1 3 7Cs analysis. 28 Table 3.2. 1 3 7 Cs Results Laboratory Depth below Sample Field pCi/g 1 3 7 Cs number surface (cm) weight (g) number CFH0003 0-3 21.09 A 0.52044+/- 11.62% CFH0306 3-6 32.54 B 0.55329 +/- 8.27% CFH0609 6-9 24.98 C 0.56418 +/- 10.45% CFH0910 9-10 9.60 Da 0.85196+/- 8.86% CFH1011 10-11 36.10 Db 0.39404 +/- 9.37% CFH1112 11 -12 25.01 Dc 0.47202+/- 11.11% CFH1215 12-15 19.09 E 0.11345 +/-48.38% CFH1518 15-18 21.10 F 0.04376+/- 103.16% CFH1821 18-21 24.42 G 0.06302 +/- 36.46% CFH0910 21-24 17.40 H 0.07885 +/- 70.30% 29 2.7 DISCUSSION 2.7.7 Origin of Sand Sheets Two landward-thinning and landward-fining sand sheets preserved in coastal marshes at Fair Harbour, Neroutsos Inlet, and Koprino Harbour are best explained as tsunami deposits. The lower sand sheet is similar in stratigraphic position, sedimentology, and age to tsunami deposits on the Pacific coasts of Oregon, Washington, and southern Vancouver Island that have been attributed to the most recent large earthquake(s) on the Cascadia subduction zone about 300 yr ago (Atwater et al., 1995). The stratigraphic position and age of the lower sand sheet are similar at the three studied marshes, thus the deposit likely records a single tsunami that affected all of the sites. The upper sand sheet probably was deposited by the tsunami of the 1964 Alaska earthquake. Stratigraphic and sedimentological observations consistent with deposition by tsunamis include the following (Fig. 2.12): (1) The sands are landward-thinning sheets that blanket paleo-marsh surfaces; (2) the sediment fines landward away from tidal channels; (3) the sand sheets rise towards the forest edge; (4) the sands contain marine microfossils; (5) some sands are normally graded or locally comprise two or more couplets deposited by discrete surges of water; (6) the sand sheets are similar in age and stratigraphic position to known tsunami deposits farther south along the Cascadia subduction zone. Other processes, such as floods and storm surges, do not account for all these characteristics. The deposit of a river flood should fine towards the sea and contain few or no marine microfossils. By contrast, the lower sand sheet at Fair Harbour fines inland and contains middle- and lower-marsh and upper tidal-flat diatoms, as well as some strictly marine species, showing that it was deposited by a landward-directed surge of water. Furthermore, all three study sites are distant from fluvial influences. Storm surges are generally erosive events characterized by net seaward movement of sediment (Long et al., 1989). The presence of only two sand sheets at the study sites, the 30 to _co$ CD 2 £ ° OTD I 5 2 co CO_cO I " T3CJ5 COO CCOi CO CO $'o T3 CD C D) -__5 2g *•* co •4—' • -CD-C t^ CD C0O5 - C - C O ) 0) C r -"o'CD -err 2 CO . _o CO »- o 5 8 2 > CO CD CL CO Q. CO _C0 CD c c CO . C CO 0 3 CD C C D 1 -O_C0 ^ ^ QOOD >^ CD" g o co co (— T— _co to" CO TJ i _ CO 5 o CD CD Z3 C c C CO = co * c CD.E > CD OCT 0 - - ± ; C g =! ~ S CO C C0O5 C D CD CO C CO CO c o jo c j-ro) c o . £ $ -2 _co a>-* . D_co=. CO $J= Q-O Q. _.aE O CD £ 1X1-1- • _ C 0 . CD C CO' CD > CO O-O c co CD-C Of£ 0 _ •+-• >—~ C 0 0 Q. E 0 5 . - CL . "cD.W^ CO-CO) £® -^ • K CD CD CO 5-O CO . --CD CD CDDXO £©OT III o Z. ODD CO CD JX. CO cr _c • •c c CO;F 1-^ o ^ c o 2 C H — o 2 Cfl-D n CO .9ir>~ -CO) CLO) C O T -1— co co "co o =1 CO > CD< O) -«CD C CL • - co co 0 -—; CO E Z 02 4-» ' to o PL, cd c 3 CO O (U -*-» 3 cd J3 u CN O O CL CD CO i C N a bJO CD E o CD CD CD N CO c CO O JO CO CO o 1— o CL — co c.9? "*3 CD CO 4-> 1— C" "t-H — CO CD < 31 lack of sedimentary structures indicative of prolonged inundation, and the remoteness of the sites from open water and Pacific storms argue against storm surges as the agent of deposition for the sand sheets. 2.7.2 Age of Sand Sheets Radiocarbon ages on fossil plant material associated with the lower sand sheet show that it was deposited since about A.D. 1660. The lack of any written record of a tsunami, prior to 1964, since the first significant European settlement on Vancouver Island in about A.D. 1850 further limits the age of the sand sheet to between about A.D. 1660 and 1850. This age control allows correlation with a plate-boundary earthquake, or a series of such earthquakes, that produced very similar deposits in coastal Oregon, Washington, and on central Vancouver Island about 300 yr ago (Atwater et al., 1995; Nelson et al., 1995). This correlation is strengthened by the absence of stratigraphic evidence for more than one tsunami of about this age at the three study sites and at other sites on Vancouver Island where similar deposits have been found (Clague and Bobrowsky, 1994b). 137cs data (Fig. 2.11, Table 2.2), accounts of wave damage at or near all three study sites, and the absence of unusually large historical storms indicate that the upper sand sheet was deposited by the 1964 Alaska tsunami. The similarity of this sand sheet to well dated deposits of the 1964 tsunami at Port Alberni (Clague et al., 1994) further supports this conclusion. The presence of only two tsunami deposits at the three study sites is due to the youthfulness of tidal marshes on northern Vancouver Island. Late Holocene emergence at net rates of up to a few millimeters per year (Clague et al., 1982; Friele and Hutchinson, 1993), which has continued into the twentieth century (Dragert, 1995; Hyndman and Wang, 1995), probably accounts for this short record. High-precision radiocarbon ages show that the most recent Cascadia plate-boundary earthquake(s) occurred between A.D. 1700 and 1720 (Nelson et al., 1995). Unavoidable 32 imprecision in this numerical dating allows for two interpretations of the seismicity: multiple magnitude-8 earthquakes may have affected different parts of the subduction zone during this 20-yr period, or one magnitude-9 earthquake may have ruptured the entire plate boundary (Heaton and Hartzell, 1987). The singularity of the ca. 300-yr-old sand sheet on Vancouver Island and high peat accumulation rates in the studied marshes preclude a hiatus of more than a decade between successive tsunamis that deposited sand in these marshes. A hiatus of a few years or less between successive tsunamis would probably be too short to produce stratigraphic separation of multiple sand sheets. 2.7.3 Depositional Processes Little is known about the transportation and deposition of sediment by tsunamis. The tsunami sediments that we studied are commonly massive, although some deposits have internal structure. The massive nature of most of the sediments suggests that sedimentary structures either are not produced or are not preserved. An insufficient or homogenous source of sediment, highly turbulent flow conditions, or extremely high or low water velocities might limit the production of graded beds, ripples, or other sedimentary structures. The rarity of internal structure may also be due to syndepositional and postdepositional modification of the sand by wind, waves, tides, and bioturbation. Both sand sheets at Fair Harbour are locally layered (Fig. 2.7). Three couplets in the upper sand sheet may record the flood and return flows of successive discrete waves of the 1964 tsunami. Tide gauge records from Tofino show that the 1964 tsunami arrived on the west coast of Vancouver Island as three 1- to 3-m-high waves over a period of about three hours (Spaeth and Berkman, 1967). 33 2.7.4 Comparison of 1964 and 300-Yr-Old Tsunamis Local bathymetry, shoreline aspect, onshore topography, and other factors affect wave amplitude and run-up (Van Dorn, 1965), making comparisons between tsunamis at even nearby sites difficult. The 1964 Alaska tsunami, however, is a modern analog of the 300-yr-old event, and the deposit of this tsunami can be used to evaluate the older event. Site comparisons can be made between the two tsunamis because bathymetry and topography have not changed significantly over the last 300 years. These comparisons ignore differences in tidal conditions and wave directions. Differences in the amount of sediment available for transport and the depositional and erosional characteristics of the tsunamis also complicate these comparisons, but cannot be resolved at present. We compared the sand sheets at the three marshes and found that the 1964 sand sheet is similar in thickness at each marsh, whereas the 300-yr-old sand sheet is thicker and more continuous at the southernmost site than at the two northern sites. At Fair Harbour, the southernmost site, the lower sand sheet has an average thickness of 2 cm and is as continuous as the 0.75-cm-thick upper sand sheet. This comparison implies that the 300-yr-old tsunami was larger there than the 1964 tsunami (Fig. 2.13). In contrast, at Koprino Harbour, the northernmost site, the 300-yr-old deposit has an average thickness of less than 0.5 cm and is not as continuous as the 0.5-cm-thick 1964 deposit (Fig. 2.13). This suggests that the 300-yr-old tsunami was smaller there than the 1964 tsunami. These observations collectively imply that the 300-yr-old tsunami attenuated to the north. A tsunami of a far-field earthquake or an earthquake directly off northern Vancouver Island would not attenuate in this fashion. We infer that this tsunami had a source south of the Nootka fault zone and that the 300-yr-old rupture on the Cascadia subduction zone did not extend north of the Nootka fault zone. 34 o co CO CD c o CD CD J= CO " D c CO CO Koprino Harbour 4 -i 0 0 4 8 10 Thickness of 300-yr-old sand sheet (cm) Fair Harbour C D ^ H — O o CO CD CO - C CD CO .p § -*= co 4 -i 2 -0 • • • • • • • JSTtlf • + - ! - » — , — t — i — , — , — T 4 6 8 10 0 2 Thickness of 300-yr-old sand sheet (cm) Figure 2.13. Comparison of thicknesses of the 1964 and 300-yr-ago tsunami deposits at individual sampling locations at Fair Harbour and Koprino Harbour. The 300-yr-old sand sheet is thicker and more continuous than the 1964 sand sheet at Fair Harbour. In contrast, the 300-yr-old sand sheet is about the same thickness as the 1964 sand sheet at Koprino Harbour. This suggests that the 300-yr-old sand sheet was deposited by a tsunami generated south of the study area. 35 2.8 CONCLUSIONS Peat beneath three marshes on northern Vancouver Island contains sand sheets deposited by the 1964 Alaska tsunami and by an older tsunami that we attribute to the most recent plate-boundary earthquake(s) on the Cascadia subduction zone about 300 yr ago. Stratigraphic and sedimentological study of the two sand sheets has provided detailed descriptions of deposit geometry and characteristics. The sand sheets are anomalous, landward-thinning and landward-fining deposits that blanket paleo-marsh surfaces. The deposits are commonly massive, but in places are normally graded or consist of couplets that probably record the surge and return flows of successive waves in a tsunami wave train. The sands contain marine microfossils, indicating that they were deposited by landward-directed flows. These characteristics may facilitate recognition of tsunami deposits in other settings. The discovery of ca. 300-yr-old tsunami deposits on northern Vancouver Island extends the effects of Cascadia subduction zone seismicity north of the Nootka fault zone. The presence of only one sand sheet of this age at the studied marshes and at other sites farther south is consistent with a single, extremely large (magnitude 9), Cascadia earthquake. In contrast to the 1964 sand sheet, the 300-yr-old deposit thins and becomes less continuous to the north. This indicates a southerly earthquake source (i.e. the boundary between the Juan de Fuca and North America plates), as opposed to a source directly off northern Vancouver Island. Further, it suggests to us that plate-boundary rupture may not have extended north of the Nootka fault zone during the most recent Cascadia subduction zone earthquake(s) about 300 yr ago. 36 CHAPTER 3 LITHOFACIES ANALYSIS; IMPLICATIONS FOR RELATIVE SEA LEVEL TRENDS AND NEOTECTONICS ON VANCOUVER ISLAND, BRITISH COLUMBIA 3.1 ABSTRACT We present a lithofacies method used to estimate relative sea level change on the west coast of Vancouver Island, British Columbia, since the most recent earthquake on the Cascadia subduction zone about 300 yr ago. We compare the present elevation of the pre-earthquake surface, which is delineated by a tsunami sand sheet, with the elevation limits of the lithofacies in which it occurs. At a site south of the Nootka fault zone, which is the northern boundary of the subducting Juan de Fuca plate, we estimate 0.2 to 1.6 m of coseismic subsidence and 1.1 m of emergence since the earthquake. In contrast, at two sites north of the Nootka fault zone, where there is no obvious stratigraphic evidence for coseismic land level change, we calculate that there has been between 0.1 and 1.7 m of submergence since the earthquake. The apparent lack of significant coseismic subsidence or interseismic emergence at the northern sites in the past 300 yr suggests that subduction and rupture on the Cascadia subduction zone do not extend north of the Nootka fault zone. Our method can be used to decipher recent changes in land level and sea level on both tectonically active and passive coastlines. 37 3.2 INTRODUCTION In this paper we use a lithofacies method to estimate relative sea level change at tidal marshes on the west coast of Vancouver Island, British Columbia. Our objective is to determine tectonically induced land level changes at the northern end of the Cascadia subduction zone. The intertidal marsh ecosystem is controlled mainly by salinity and inundation, which vary with elevation (Chapman, 1977). As a result, there are distinct vertically zoned lithological and biological facies in tidal marshes. This zonation can be applied to intertidal sediments underlying marshes. Relative sea level change since the deposition of a marker bed or since the burial of a surface of known age can be estimated by comparing the present elevation of the bed or surface with the elevation range of the lithofacies or biolithofacies in which it occurs. We employ this method at localities where paleo-marsh surfaces were covered by a tsunami deposit about 300 yr ago during the most recent plate-boundary earthquake on the Cascadia subduction zone (Fig. 3.1). Three lithofacies are described and their elevation ranges are determined with respect to present sea level. The present elevation of the pre-earthquake surface, which is the base of the tsunami sand sheet, and the elevation range of the lithofacies containing the pre-earthquake surface are compared in order to estimate the amount of relative sea level change since the earthquake. Comparisons of the magnitude and direction of relative sea level change at Tofino, a site south of the Nootka fault zone, and Fair Harbour and Koprino Harbour, two sites north of the Nootka fault zone, suggest that there are fundamental differences in the tectonic environment at the northern end of the Cascadia subduction zone. 38 Figure 3 . 1 . Map of the study area. Solid circles are study sites. Inset map shows lithospheric plates and the seaward edge of the Cascadia subduction zone. 3 9 3.3 SETTING Vancouver Island is located at the north end of the Cascadia subduction zone, a 1000-km-long region where the oceanic Juan de Fuca and Gorda plates subduct below the continental North America plate (Fig. 3.1). The Nootka fault zone separates the Juan de Fuca plate from the Explorer plate to the north. Once thought to be a separate small plate moving eastward beneath North America (Riddihough, 1984), the Explorer plate is now regarded to be a broad deformational zone where convergence on the Cascadia subduction zone to the south is transformed into strike-slip motion along the North America-Pacific plate boundary to the north (Rohr and Furlong, 1995). This suggests that the tectonic environment of northern Vancouver Island, north of the Nootka fault zone, may be fundamentally different from that of southern Vancouver Island. There is compelling geological and geophysical evidence for past plate boundary earthquakes and continuing subduction on the Cascadia subduction zone (Atwater et al., 1995; Hyndman, 1995). Buried marsh and forest soils at estuaries in Oregon, Washington, and on southern Vancouver Island are evidence for coseismic subsidence during large earthquakes. Sand sheets which mantle some of the soils were deposited by tsunamis triggered by these earthquakes (Atwater et al., 1995, Benson et al., submitted). Geodetic data from leveling lines, tide gauges, gravity surveys, and a Global Positioning System network indicate that the coast is presently uplifting at rates of a few mm/yr, presumably due to interseismic accumulation of elastic strain above the locked subduction zone (Savage et al., 1991; Dragert et al, 1994; Hyndman and Wang, 1993, 1995). The cycle of coseismic subsidence and interseismic uplift in Cascadia is similar to cycles at subduction zones in Alaska and Japan where there have been great (magnitude 8+) earthquakes in historical time (Thatcher, 1984; Savage and Plafker, 1991). Tidal marshes at Tofino, Fair Harbour, and Koprino Harbour were chosen for this study because they have well documented stratigraphies, contain two tsunami sand sheets that serve as marker horizons, and are located on opposite sides of the Nootka fault zone (Fig. 40 3.1). The marshes are underlain by about 1 m of peat, which in turn, overlies younger sand and gravel deposited during a transgression about 6000-7000 yr BP and then reworked during a late Holocene regression (Friele and Hutchinson, 1993; Clague and Bobrowsky, 1994a, Benson et al., submitted). The sand and gravel unconformably overlie late Pleistocene glaciomarine clayey silt (Clague and Bobrowsky, 1994a). The mean tide range at the three study areas is about 2.8 m, and the maximum range is 4.5 m (Fisheries and Oceans, 1995). Marsh sediments at Tofino contain a buried soil and an overlying tsunami sand sheet resulting from the 300-yr-ago Cascadia plate-boundary earthquake (Fig. 3.2A; Clague and Bobrowsky, 1994a, b). The base of the tsunami sand sheet delineates the pre-earthquake surface. Analysis of microfossils in the buried soil and in tidal mud above the tsunami sand indicates that there was between 0.2 and 1.0 m of subsidence during the earthquake (Guilbault et al., 1995). A thin discontinuous layer of silt and sand near the top of the peat was probably deposited by the tsunami of the great Alaska earthquake in 1964 (Clague and Bobrowsky, 1994a, b). The stratigraphies at Fair Harbour and Koprino Harbour (Fig. 3.2B), north of the Nootka fault zone, are similar to the stratigraphy at Tofino, but lack the conspicuous soil and overlying tidal mud produced by coseismic subsidence. In addition, the deposit of the 300-yr-old tsunami is thinner and less continuous at the northern sites than at Tofino, implying a tsunami source south of the Nootka fault zone (Benson et al., submitted). 41 Figure 3.2A. Buried marsh soil and ca. 300-yr-old tsunami sand sheet in outcrop near Tofino. The buried soil and tsunami sand are overlain by intertidal mud which was deposited when the marsh was abruptly submerged below the level of the peat/mud lithofacies boundary. 42 Figure 3.2B. Ca. 300-yr-old tsunami sand sheet in outcrop at Fair Harbour (arrow). Facies above and below the sand are the same, indicating that the marsh did not submerge below the peat/mud lithofacies boundary at the time of the earthquake. Shovel is 60 cm long. 43 3.4 LITHOFACIES DESCRIPTIONS Three lithofacies are easily identifiable in outcrops and cores at marshes on Vancouver Island: tidal mud, marsh peat, and upland soil facies (Fig. 3.3). These facies are deposited at different elevations because of differences in salinity and duration of inundation (Chapman, 1977). The elevation of each lithofacies boundary is unique at each of the study sites due to local tidal differences, and must be determined independently. 3.4.1 Tidal Mud The tidal mud lithofacies comprises olive gray clayey silt. The sediment is commonly massive due to bioturbation by marine organisms, but laminations may be present. Deposition is controlled by tidal range, current velocities, sediment availability, and particle size. The tidal mud lithofacies occurs from lower low water (LLW) to mean sea level (MSL). 3.4.2 Marsh Peat This lithofacies consists of brown fibrous peat and muddy peat. The peat is derived from salt-tolerant plants living on the marsh surface; interstitial silt and clay are deposited from suspension when the surface is tidally flooded. Rapid production and burial of plant material result in acidic anoxic conditions that retard organic decomposition. Peat stratigraphies are commonly massive due to rooting action from the vegetated surface, but large low-frequency events such as storms, floods, or tsunamis may deposit distinct clastic layers in peat. The peat lithofacies occurs in the upper half of the intertidal zone from MSL to higher high water (HHW). 3.4.3 Upland Soil The upland soil lithofacies is composed of brown to black, finely rooted, crumbly grass or forest soil. It occurs above HHW. 44 Figure 3.3. Marsh near Tofino, British Columbia, showing tidal mud (M), marsh peat (P), and upland soil (S) lithofacies. 45 3.5 LITHOFACIES METHOD Depths of contacts, sediment types, colors, and textures recorded at the marshes (Clague and Bobrowsky, 1994a; Benson et al., submitted) were used to produce average sections that best represent the stratigraphies. The elevation ranges of the lithofacies were determined at each of the study areas from leveling surveys linked to tide gauge data. Net relative sea level change since the most recent earthquake on the Cascadia subduction zone can be estimated by determining the change in elevation of the pre-earthquake surface (Fig. 3.4, Table 3.1). This surface is delineated by the tsunami sand sheet deposited ca. 300 yr ago at the time of the earthquake. The elevation range of the lithofacies containing the pre-earthquake surface is compared to the modern elevation of the that surface; the difference between the two is the net relative sea level change in the past 300 yr. Changes in lithofacies, which indicate that the land surface migrated across a lithofacies boundary, provide additional elevation information. Vertical ranges and elevations of the lithofacies zones are accurate to within about a decimeter and probably have not changed in the last 300 yr. 3.6 RESULTS 3.6.1 Tofino The pre-earthquake surface at Tofino occurs in peat similar to that found directly below the modern marsh, demonstrating that this surface was situated somewhere within the elevation range of the peat lithofacies 300 yr ago (Fig. 3.4A, a and b). Because there is 0.2 m of tidal mud above the tsunami sand, the pre-earthquake surface submerged at least 0.2 m below the peat/mud lithofacies boundary at the time of the earthquake. This is a minimum value for submergence and assumes that the pre-earthquake marsh surface was located at the bottom of the peat lithofacies zone (Fig. 3.4A, a). If, on the other hand, the pre-earthquake surface was situated at the top of the peat lithofacies zone, it experienced at least 1.6 m of 46 Lithofacies 3.9m A. Tofino Earthquake -300 yr ago Present Range of pre-earthquake surface 1*4 T c >0.2-1.6 m of coseismic subsidence >1.1 m of net emergence Range of pre-earthquake surface la 0.1 -1.7 m of net submergence C. 3.9m Koprino Harbour 2.8m Range of pre-earthquake surface b 4t 0.1 -1.2 m of net submergence Upland soil lithofacies I—~l Marsh peat lithofacies [003 Tidal mud lithofacies Tsunami sand Pre-earthquake surface Figure 3.4. Results of lithofacies analysis at three marshes on Vancouver Island. The pre-earthquake surface at all three sites was situated somewhere within the peat lithofacies (a and b correspond to upper and lower limits, respectively). At Tofino, this surface subsided at least 0.2 m below the mud/peat lithofacies boundary at the time of the earthquake. Since then, it has experienced at least 1.1 m of interseismic emergence to its present elevation (c). At Fair Harbour and Koprino Harbour, there is no stratigraphic evidence for coseismic subsidence, and the 300-yr-old surface has migrated from some-where within the peat lithofacies to its present position. 47 cn CO T 3 C J3 o co 00 c - C o cn CO C/3 o CM c 03 CO cn o U CO 00 C cj _S CJ 13 > cu CU o3 CN 3 03 CO o CO % 3 cr CO i co 3 O > CO 3 CO cn CO CO bo cn CO '53 -^H o CN ifi co 1 <+H o J3 co co -3 in Td cn A vo CN d A s CO O 3 O H CO CO 3 CO o o >H CO E CO CO o 3 co T d 'cn 3 cn CN V Ov in CN E CO o 3 co 00 >-c CO 3 co 3 O 2 £ ON co CN E ON co i C O CN t--CN 3 .3 O 03 -P o3 CN co co 3 co 00 1— co X) 3 in co g o\ co" CN ON co 00 CN CN CN o fa 3 3 W X >H 3 O •e cS X o _s 'C P H O ts 3 CO cS co o in m d ll 0 1/3 fa *-i •e E cs 3 K 2 cS PH -t—» 03 3 CO 3 cn cS CO OO VO 3 3 ° II co PH cn cS cn X) CO co '53 00 ,cS co ja > 3 o < J Z '—1 CN CO 48 coseismic submergence (Fig. 3.4A, b). The pre-earthquake surface at Tofino is presently 0.9 m above the peat/mud lithofacies boundary. Therefore, the pre-earthquake surface has emerged at least 1.1m since the earthquake 300 yr ago (Fig. 3.4A, c). 3.6.2 Fair Harbour and Koprino Harbour The pre-earthquake surface at both Fair Harbour and Koprino Harbour is marked by a tsunami sand sheet and occurs in peat similar to that found, directly beneath the modern marshes. This indicates that the surface was situated somewhere within the elevation range of the peat lithofacies immediately before the earthquake. It is presently about 0.1 m below the elevation of the peat/mud lithofacies boundary. Because it is overlain by peat, the surface did not subside below the peat/mud lithofacies boundary at the time of the earthquake. The minimum and maximum net sea level change since the tsunami 300 yr ago can be determined from the lowest and highest elevations of the peat lithofacies zone. At Fair Harbour, there has been between 0.1 and 1.7 m of net submergence (Fig. 3.4B, a and b) in the last 300 yr.. At Koprino Harbour, the pre-event surface has experienced between 0.1 and 1.2 m of net submergence (Fig. 3.4C, a and b) during this period. 3.7 DISCUSSION 3.7.1 Causes of Relative Sea Level Change Four mechanisms might account for the relative sea level changes on Vancouver Island: (1) tectonism, (2) eustatic sea level change, (3) isostatic land level change, (4) autocompaction of peat. We propose that relative sea level changes recorded by marsh lithofacies on Vancouver Island over the last 300 yr result mainly from tectonically induced land level changes and eustatic sea level change, and that other mechanisms are less important. Glacio-isostatic rebound in response to deglaciation at the end of the Pleistocene 49 was largely complete thousands of years ago (Clague et al., 1982, Friele and Hutchinson, 1993), although it is possible that very small, residual isostatic adjustments are occurring today. Autocompaction is significant in some salt marshes in the southeastern United States, but the highest rates are associated with thick, decomposing peat sequences in sensitive subsiding microtidal environments (Cahoon et al., 1995). In contrast, the peats we studied on Vancouver Island are competent, less than 1 m thick, and occur in a mesotidal environment. While we cannot quantify the effect of autocompaction, we believe it to be negligible. Of the four mechanisms mentioned above, only tectonism would likely affect our study sites differently. Autocompaction at the three sites is probably similar because the stratigraphies are nearly identical; eustatic sea level changes have been the same at all sites; and the study sites had similar Pleistocene ice loads and therefore similar Holocene isostatic histories. 3.7.2 Accuracy of the Lithofacies Method We can test our lithofacies method using published microfossil and geodetic data from Tofino. Our method indicates that the marsh at Tofino submerged between 0.2 and 1.6 m during the 300-yr-old earthquake (Table 3.1); this is similar to an estimate of 0.2 to 1 m of coseismic subsidence obtained independently by microfossil analysis (Guilbault et al., 1995). Possible differences in the rates of immediate post-seismic uplift and longer term aseismic uplift (Savage and Plafker, 1991) complicate interpretations of our emergence data. Nevertheless, our average uplift rate at Tofino over the last 300 yr, corrected for the present global eustatic sea level rise of 1.8 mm/yr (Douglas, 1991), is 5.5 mm/yr, which is similar to the geodetically measured rate of about 5 mm/yr from a level line in the same area (Hyndman and Wang, 1995). 50 3.7.3 Tectonic Implications Our estimates of relative sea level change at the three study sites carry important tectonic implications. Geodetic and heat flow data suggest that the thrust fault separating the Juan de Fuca and North America plates is locked, and that convergence of about 4 cm/yr is accommodated by gradually dragging the toe of the continent down while producing an inland flexural bulge (Hyndman and Wang, 1993, 1995; Dragert and Hyndman, 1995; Hyndman, 1995). Elastic dislocation models predict that this strain would be released elastically, and the flexural bulge would abruptly subside, during a great earthquake. Our estimates of 0.2 to 1.6 m of coseismic submergence and at least 1.1 m of post-seismic emergence at Tofino are consistent with these models. Net submergence at Fair Harbour and Koprino Harbour (Table 3.1) is probably due mainly to eustatic sea level rise. The lack of stratigraphic evidence for coseismic subsidence at these sites suggests that this region was not directly affected by the Cascadia earthquake 300 yr ago. The absence of interseismic emergence at these sites, which would indicate continuing subduction, supports this conclusion. We suggest that the tectonic setting north of the Nootka fault zone is different from that to the south, and that subduction and rupture on the Cascadia subduction zone do not extend north of central Vancouver Island. 3.8 CONCLUSIONS We use vertically zoned marsh lithofacies to estimate net relative sea level change and tectonic land level change on the west coast of Vancouver Island since the most recent earthquake on the Cascadia subduction zone about 300 yr ago. Comparison of the elevation range of a lithofacies and the present position of a dated surface within this lithofacies provides maximum and minimum estimates of relative sea level change since deposition. This method is generally applicable in situations where lithofacies have limited, well defined elevation ranges and where one or more dated surfaces or marker beds are present. 51 Marshes on Vancouver Island comprise three distinct environments, each of which has an associated lithofacies, i.e. tidal mud, marsh peat, and upland soil. We determined relative sea level change since the earthquake at three marshes on Vancouver Island by comparing the present elevation of a tsunami sand that mantles the pre-earthquake surface with the elevation range of the lithofacies in which it was deposited. From these We calculate 0.2-1.6 m of coseismic submergence and at least 1.1 m of interseismic emergence at Tofino, south of the Nootka fault zone. These values are consistent with expected coseismic and interseismic deformation at a locked subduction zone and are in agreement with published microfossil and geodetic results. We see no stratigraphic evidence for coseismic subsidence at Fair Harbour and Koprino Harbour, north of the Nootka fault zone. Furthermore, these sites have experienced somewhere between 0.1 m and 1.2-1.7 m of post-seismic submergence in the last 300 yr. The lack of coseismic subsidence and interseismic uplift at Fair Harbour and Koprino Harbour suggests that subduction and attendant plate-boundary rupture do not extend north of the Nootka fault zone. Our method can be applied to stratigraphies containing multiple buried soils to better understand and quantify the cycle of interseismic emergence and coseismic subsidence in Cascadia. Comparisons of land level changes during past seismic cycles with land level change since the most recent earthquake 300 yr ago might provide clues about the timing of the next rupture of the Cascadia subduction zone. 52 CHAPTER 4 CONCLUSIONS 4.1 SUMMARY Marshes on northern Vancouver Island contain sand sheets deposited by the 1964 Alaska tsunami and the most recent plate-boundary earthquake on the Cascadia subduction zone about 300 yr ago. Trenching, coring, and analysis of the two sand sheets have provided detailed descriptions of deposit geometry and characteristics. Tsunami sand sheets on northern Vancouver Island are stratigraphically unique, landward-thinning and landward-fining deposits that blanket paleo-marsh surfaces. The deposits are commonly massive, but in places are normally graded or consist of couplets attributed to the surge and return flow of successive waves in a tsunami wave train. The sands contain marine microfossils, indicating that they were deposited by a landward-directed flow of water. These characteristics will facilitate recognition of tsunami sediments in other settings. The discovery of the 300-yr-old tsunami deposits on northern Vancouver Island extends the known effects of Cascadia subduction zone seismicity north of the Nootka fault zone. The presence of only one ca. 300-yr-old sand sheet at the studied marshes and at other sites farther south is consistent with a single, extremely large (magnitude-9), Cascadia earthquake. Two methods were employed to assess the tectonic setting of Vancouver Island. Comparison of the two tsunami sand sheets reveals a possible source area for the 300-yr-old earthquake. Whereas the 1964 deposit is similar at all of the study sites, the 300-yr-old deposit thins and becomes less continuous to the north. This suggest a southerly (i.e. Juan de Fuca plate) source, rather than a source directly off northern Vancouver Island, for the most 53 recent earthquake on the Cascadia subduction zone. Vertically zoned marsh lithofacies were used to estimate net relative sea level change and tectonic land level change on the west coast of Vancouver Island since the most recent Cascadia subduction zone earthquake. Coseismic and post-seismic land level changes since the earthquake were determined by comparing the present elevation of the pre-earthquake surface with the elevation range of the lithofacies in which it was deposited. Estimates of 0.2-1.6 m of coseismic submergence and at least 1.1 m of interseismic emergence south of the Nootka fault zone at Tofino are consistent with expected coseismic and interseismic deformation at a locked subduction zone, and are in agreement with published microfossil and geodetic data. There is no obvious stratigraphic evidence for coseismic subsidence at Fair Harbour and Koprino Harbour, north of the Nootka fault zone. Estimates of post-seismic relative sea level change at these two sites range from 0.1 m and 1.7 m of submergence, likely resulting from eustatic sea level rise. The lack of tectonically induced land level change at the northern sites suggests that subduction and earthquakes may not extend north of the Nootka fault zone. 4.2 FUTURE WORK The 1964 tsunami provides a modern analog for the 300-yr-old tsunami. Additional sedimentological analysis and comparison of the two tsunami deposits could produce an estimate of the magnitude and source characteristics of the most recent Cascadia tsunami (Satake etal., 1996). The mechanisms responsible for tsunami sediment deposition are poorly understood. Coarse/fine sediment couplets found within deposits on Vancouver Island most likely result from successive waves in a tsunami wave train. Detailed stratigraphic and sedimentological study of these couplets could provide an estimate of the number and magnitude of waves 54 produced during a subduction zone earthquake. Broader application and refinement of the lithofacies method developed in Chapter 3 could better quantify coseismic and interseismic land level change along the entire length of the Cascadia subduction zone. In addition, this method could be useful in other settings where there are distinct, vertically zoned lithofacies. Determining the elevation of the 300-yr-old peat/soil lithofacies boundary at the forest edge would allow for more precise estimates of the pre-earthquake surface elevation within the peat lithofacies. This, and comparison of results from this method and those of microfossil and geodetic analyses, would provide further definition of coseismic and post-seismic land level change. 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C , Lisowski, M. , and Prescott, W. H., 1991, Strain measurements and the potential for a great subduction zone earthquake off the coast of Washington: Science, v. 252, p. 101-103. Satake, K., Shimazaki, K., Tsuji, Y., and Ueda, K., 1996, Time and size of a giant earthquake in Cascadia inferred from Japanese tsunami records of January 1700: Nature, v. 379, p. 246-249. Spaeth, M . G., and Berkman, S. C , 1967, The tsunami of March 28, 1964, as recorded at tide stations: Coast and Geodetic Survey, Bulletin No. 33, 86 p. Stuiver, M. , and Becker, B., 1993, High precision decadal calibration of the radiocarbon time scale, AD 1950-6000 BC: Radiocarbon, v. 35, p. 35-65. Stuiver, M. , and Pearson, G. W., 1993, High-precision bidecadal calibration of the radiocarbon time scale, AD 1950-500 BC and 2500-6000 BC: Radiocarbon, v. 35, p. 1-23. Thatcher, W., 1984, The earthquake deformation cycle at the Nankai Trough, southwest Japan: Journal of Geophysical Research, v. 89, p. 3087-3101. Yamaguchi, D. K., Woodhouse, C. A., and Reid, M . S., 1989, Tree-ring evidence for synchronous rapid submergence of the southwestern Washington coast about 300 years ago [abs.]: Eos (Transactions of the American Geophysical Union), v. 70, p. 1332. Van Dorn, W. G., 1965, Tsunamis. In "Advances in Hydroscience" (V. T. Chow, Ed.), Academic Press, New York, pp. 1-48. 60 APPENDIX 1 FAIR HARBOUR DATA Fair Harbour marsh is located at UTM coordinates 5558250N, 636000E. It is about 1 hour from Zeballos by road. Road conditions vary from fair to poor, and logging trucks are a hazard. Travel west out of Zeballos over the Zeballos River bridge. Continue past Little Espinoza Inlet where the road turns north. Continue on to the next main junction and head west. The road was signed during the summer of 1995. A road along the south side of the marsh provides easy access to the field area (see Fig. 2.3A). Camp sites are available at the head of the inlet. 61 64 65 66 68 E o cn 70 71 Fair Harbour L20, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Refusa number edge elevation top bottom top bottom contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) 0 5.49 1.78 1.78 0 35 5.5 2.82 7 8 72 76 92 114 10 2.68 9 10 69 72 87 122 15 19.1 19.11 2.7 2.28 1.91 9.5 10.5 71 74 98 120 20 1.91 37 43 50 90 25 1.91 65 30 33.7 33.71 1.85 1.85 2.83 5.5 8 44 50 100 35 2.83 9 10 85 87 142 40 41.4 41.41 2.82 2.82 1.78 12.5 13.5 89 94 133 155 45 1.79 21 50 54.99 1.74 1.78 34 55 2.55 4 5 39 40 65 115 60 2.8 7.5 8.5 62 62.5 82 148 65 2.83 8 9.5 61.5 62 72 143 70 2.83 0 3.5 51 51.5 69 151 75 2.87 7 8 63 65 80 154 80 2.92 7.5 8.5 63.5 64.5 85 145 85 2.91 4 5.5 57 58 73 160 90 2.9 8 9.5 64 65 78 150 73 Fair Harbour L15, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Refusa lumber edge elevation top bottom top bottom contact (m) (m) ( L L W . m ) (cm) (cm) (cm) (cm) (cm) (cm) 0 1.86 35 4.99 2.08 5 2.83 7 7.5 73 75 97 120 10 2.84 7.5 8.5 68 70 74 120 15 2.75 8.5 9.5 74 80 96 122 18.5 2.46 18.51 2.11 19.1 2.11 19.11 2.46 20 2.46 50 52.5 76 89 20.8 2.46 20.81 1.86 22.8 1.86 22.81 2.16 25 2.48 47.5 50 79 104 29 2.67 29.01 1.97 30 1.97 9.5 10.5 73 75 103 120 32.5 1.97 32.51 2.67 35 2.85 8 9 88 92.5 107 150 40 2.81 10.5 11.5 83 87 105 145 40.6 2.81 40.61 1.91 45 1.79 ' 0 20 50 1.71 0 20 53.5 1.88 53.51 1.89 55 2.87 10 10.5 74 76 109 129 60 2.89 11 12 68 69.5 104 138 65 2.93 8 8.5 65 66 98 135 70 2.92 8 9.5 56 57 104 143 75 2.9 9.5 10.5 62 64 97 140 79.8 3 80 2.8 51.5 53 134 150 80.5 3 82.6 3 82.61 2.6 83.2 2.6 83.21 3 85 2.89 6 6.5 58 58.5 96 142 85.2 2.89 85.21 2.49 86.4 2.49 86.41 2.89 90 2.85 9 11 55 56.5 86 127 Fair Harbour L10, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Refusa umber edge elevation top bottom top bottom contact (m) (m) ( L L W , m) (cm) (cm) (cm) (cm) (cm) (cm) 0 1.85 25 50 3.8 1.85 3.81 2.81 5 2.81 5.5 6.5 72 73.5 79 119 10 2.82 7.5 9 78 83 94 124 15 2.59 7 8.5 63 65 86 125 20 2.73 8.5 10.5 72.5 74.5 97 140 22.4 2.73 22.41 1.98 24.4 1.95 24.41 2.7 25 2.7 11.5 12 78 80 103 132 29 2.78 29.01 2.03 30 2.03 8 10 77.5 80 110 125 32 2.03 32.01 2.78 35 2.88 6.5 7 86.5 90 115 155 39.7 2.75 40 1.8 7 8 81 84 115 140 45 1.71 20 50 1.73 10 11 67 67.1 105 135 51.45 1.73 51.46 2.88 55 2.91 10 12 62 63.5 109 146 60 2.89 9 10 61 61.1 102.5 150 65 2.91 11.5 12 69.5 70.5 110 164 70 2.84 4.5 4.7 50 50.5 83 155 .75 2.98 8 9 60.5 61.5 110 175 80 2.76 40.5 42 95 180 85 2.82 8 9 68 75 90 185 88.2 2.6 88.21 2.05 90 2.05 5 6 37 39 69 148 75 Fair Harbour L5, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Refusal number edge elevation top bottom top bottom contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) 0 1.99 27 51 2.5 2.78 5.5 6 77 79 130 5 2.82 5.5 6 68 70 76 120 10 2.81 9.5 10.5 75 76.5 89 118 15 2.81 5.5 6 71.5 73.5 103 130 18.7 2.73 18.71 2.03 20 2.03 8 9.5 76 78 96 110 22.4 2.03 22.41 2.73 24.99 2.69 25 2.19 11 12 63 64 107 128 25.7 2.19 25.71 2.69 27.2 2.92 27.21 2.62 28.1 2.62 28.11 2.92 30 2.92 9 9.5 80.5 82.5 112 146 35 2.92 9 9.5 86 88.5 137 170 37.4 2.71 37.41 1.71 40 1.71 6 6.5 73 75 110 164 45 1.69 0 17 50 1.77 7 7.5 62 62.2 110 136 50.4 2.77 55 2.93 11.5 12.5 64.5 65 109 128 60 2.9 8 9 64 65.5 88 146 63.9 3.02 63.91 2.77 65 2.77 58 60 76 140 65.9 2.77 65.91 3.02 70 2.94 6 7 57 58.5 96 152 75 2.92 6.5 7.5 61 62 91 120 76.4 2.92 76.41 2.72 76.7 2.72 76.71 2.92 80 2.92 5 5.5 62 64 92 136 83.8 2.63 83.81 2.28 84.7 2.2 84.71 2.55 85 2.55 4.5 6 27 29 64 175 85.9 2.55 85.91 2.2 90 2.08 15 68 Fair Harbour ML, 1995 Hole Bank Surface Upper sand Upper sar number edge elevation top bottom (m) (m) (LLW, m) (cm) (cm) -30 3.58 -27.5 3.39 3.5 3.7 -25 3.18 2 2.5 -22.5 3.08 2.5 3 -20 2.98 2.5 3 -16.2 1.95 7.5 8 -10 1.84 -5 1.95 0 2.89 6 7 5 2.82 6.5 7 10 2.78 5.4 6 15 2.75 10 11 18.7 2.75 18.71 2.25 19.3 2.25 19.31 2.58 20 2.58 11.5 11.9 25 2.86 9 10 30 2.92 7.5 8.5 35 2.9 8 9 36.6 2.9 36.61 1.66 40 1.66 45 1.68 49.99 1.68 50 2.83 10 11 55 2.89 9 10 60 2.92 8 9 64 2.87 64.01 2.67 65 2.67 65.6 2.67 65.61 2.87 70 2.93 4.5 5.5 75 2.83 8.5 10 75.8 2.83 75.81 2.33 76.6 2.33 76.61 2.83 79.5 2.84 79.51 2.24 80 2.24 8 9 81 2.24 81.01 2.84 84.6 2.68 84.61 2.03 85 2.03 11 12.5 Lower sand Lower sand Peat/sand Refusal top bottom contact (cm) (cm) (cm) (cm) 7.5 8 8 8 8 9 9 9 16 18 26 26 27 28 29 29 43.5 45 50 50 69.5 71 96 96 5 37 28 68 75.5 77 100 140 67 69 91 129 70 71 96 130 68.5 70 90 128 65 66 85 115 83 84 109 137 86 88 141 152 88 90.5 140 160 0 0 0 0 68 68.1 106 ? 62.5 68 87 137 61 62 96 154 39 43 63 142 58 60.5 83 170 51 52 87 192 60 61 100 205 62 65 123 155 77 Fair Harbour M L , 1995 (Continued) Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Refusal number edge elevation top bottom top bottom contact (m) (m) ( L L W , m) (cm) (cm) (cm) (cm) (cm) (cm) 86.2 2.03 86.21 2.68 90 2.47 28.5 31 79 144 78 Fair Harbour R5, 1995 Hole# Bank Surface Ele Upper Sand Upper Sand Lower Sand Lower Sand Peat/sand Refusa (m) (m) ( L L W , m) Top (cm) Bottom (cm) Top (cm) Bottom (cm) Contact (cm) (cm) 0 2.05 5.5 6 80 90 ? ? 1 2.05 1.01 2.85 5 2.86 5.5 6 71.5 72.5 99 137 10 2.82 7.5 8.5 65.5 70 106.5 130 15 2.77 7.5 8.5 72 75 111 128 16.4 2.77 16.41 2.22 17.2 2.22 17.21 2.77 20 2.82 9 9.5 79.5 80.5 106 137 25 2.85 5.5 6 83.5 86 115 143 30 2.88 7 7.5 81.5 82.5 122 151 33.6 2.88 33.61 1.08 35 1.2 0 15 38.7 1.89 38.71 2.44 39.8 2.32 39.81 1.95 40 1.95 69 45 1.76 16 47.49 1.76 47.5 1.86 12 13 79 79.2 107 135 50 2.91 5.5 6 58 58.2 104 149 55 2.93 10 10.5 64 65 102 152 60 2.94 4 5 68 70 100 163 65 2.95 4 4.5 58 59.5 99 160 70 2.97 6 6.1 67 67.2 91 138 75 2.94 9 9.5 58.5 60 ? 161 78.7 2.71 78.71 2.06 80 2.06 7 8 36 36.2 78 120 82 2.06 82.01 2.51 83.7 2.51 83.71 2.21 84.2 2.21 84.21 2.69 85 2.69 5.5 6 ?47 ?51 91 146 90 2.72 9 11 49.5 51 83 164 79 Fair Harbour RIO, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Refusa umber edge elevation top bottom top bottom contact (m) (m) ( L L W , m) (cm) (cm) (cm) (cm) (cm) (cm) 0 2.21 47 77 1.1 2.28 1.11 2.88 5 2.89 7 7.5 70.5 72.5 101 140 9.8 2.89 9.81 2.78 10 2.78 7 8 64 65 103 138 10.2 2.78 10.21 2.89 15 2.82 10 11 72 72.5 97 123 20 2.85 9.5 10 74 74.5 124 142 25 2.88 8 8.5 60.5 61 129 157 25.2 2.88 25.21 2.58 26 2.58 26.01 2.88 29.99 2.79 30 2.23 6 7 78 81 124 178 35 1.79 ? ? ? ? ? 7 35.5 1.79 35.51 2.29 39.1 2.25 39.11 1.75 40 1.75 81 45 1.85 10.5 11 68 68.5 100 142 45.3 1.85 45.31 2.85 50 2.92 9 9.5 65 67.5 98 147 55 2.95 5 6 61 63 95 153 60 2.96 7.5 9 61 63 104 173 65 2.97 6 7 61 61.5 92 155 70 2.95 7 7.5 64 65.5 105 148 74.1 2.81 74.11 2.16 75 2.16 4.5 5 51 52.5 78 136 75.8 2.16 75.81 2.81. 80 2.58 10 10.5 72 74 89 137 80.01 2.08 85 2.06 36 97 90 2.03 48 116 80 Fair Harbour R15, 1995 Hole Bank Surface Upper sand Upper sar number edge elevation top bottom (m) (m) ( L L W , m) (cm) (cm) 0 2.12 10.5 11 5 2.95 7.5 8.5 10 2.85 9.5 10 15 2.82 9 9.5 19.7 3.03 19.71 2.78 20 2.78 20.2 2.78 20.21 3.03 25 2.81 7.5 8 28 2.78 28.01 1.58 30 1.58 34.7 1.78 34.71 2.28 35 2.28 4 4.5 37 2.81 37.01 1.91 40 1.91 44 1.96 44.01 2.76 45 2.76 9 9.5 50 2.94 10 10.5 55 2.93 6 6.5 60 2.86 14 15 64.9 2.97 64.91 2.77 65 2.77 63.5 2.77 63.51 2.97 70 2.91 6 6.5 75 2.89 7 7.2 80 2.54 80.2 2.54 80.21 1.99 85 2 90 2 Lower sand Lower sand Peat/sand Refusal top bottom contact (cm) (cm) (cm) (cm) 71.5 73.5 98 118 70 72 . 100 130 69 70.5 102 128 68 70 103 136 59 62.5 85 125 80.5 82 108 140 0 15 34 36 43 65 0 10 64 67 96 124 68 70 90 151 59.5 61 92 162 62 62.2 85 145 48 51 75 148 62 63 102 156 62 63 101 138 26 27 85 105 40 92 65 101 81 Fair Harbour R20, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Refusal number edge elevation top bottom top bottom contact (m) (m) ( L L W , m) (cm) (cm) (cm) (cm) (cm) (cm) 0 2.05 43 3.8 2.18 3.8 2.98 5 2.98 7.5 8 80 81.5 104 178 10 2.93 6.5 7 63.5 65 103 130 15 2.9 7 7.5 70.5 73 110 125 17.5 2.9 17.51 2.7 19.5 2.7 19.51 2.87 20 2.87 8 8.5 63 63.7 99 146 25 2.78 9 9.5 78 79 117 140 25.7 2.78 25.71 1.88 27.4 1.88 27.41 2.58 29.3 2.58 29.31 1.78 30 1.66 10 35 1.7 14 35.5 1.7 35.51 2 36.2 2 36.21 1.7 38 1.7 38.01 2.1 40 2.19 28 45 42 2.19 42.01 2.69 45 2.87 6 6.2 56.5 58 84 146 50 2.96 6.5 7 57 59 90 158 55 2.97 4.5 5 51.5 52.5 85 153 60 2.98 6.5 7.5 56.5 59 106 155 65 2.97 5 6 61 61.5 99 161 70 3.01 4 5 60 . 61 90 133 75 2.87 6.5 7 62 63 87 166 78.5 2.17 80 2.02 46 73 85 2.01 55 112 90 2 56 126 82 Fair Harbour R25, 1995 Hole Bank Surface Upper sand Upper sand number edge elevation top bottom (m) (m) ( L L W , m) (cm) (cm) 0 2.96 8 8.5 5 2.99 8 8.5 10 2.98 6.5 7 15 2.92 10 10.5 20 2.89 10 10.5 25 2.79 9 9.5 26.3 2.79 26.31 1.89 27.8 1.89 27.81 2.54 29.4 2.54 29.41 1.93 30 1.93 33 1.93 33.01 1.73 35 1.62 39 1.73 39.01 2.13 40 2.77 10 10.5 45 2.93 50 2.98 6 6.5 55 2.99 9 9.2 60 2.98 6.5 7.5 64.99 2.99 65 2.78 5 5.5 65.4 2.78 65.41 2.99 70 2.97 9.5 10 75 2.46 75.55 2.46 75.56 2.26 80 2 85 1.99 90 1.35 Lower sand Lower sand Peat/sand Refusal top bottom contact (cm) (cm) (cm) (cm) 89 91 124 79.5 81 97 152 61 63 107 140 68 70.5 110 1470 64.5 66 109 8.5 87.5 129 153 13.5 15 78 15 52 53 70 128 56 59.5 88 154 54.5 55 88 148 53 54 92 161 61.5 62.5 87 150 57 58 104 175 65 66.5 98 156 31 33:5 52 152 54 109 75 104 63 104 83 Fair Harbour R30, 1995 Hole Bank Surface Upper sand Upper sand number edge elevation top bottom (m) (m) ( L L W , m) (cm) (cm) 1 3.04 1.01 2.24 2.5 2.24 2.51 3.04 5 2.99 10 3 8 8.5 15 2.93 7.5 8.5 20 2.87 12 12.5 25 2.74 25.7 2.74 25.71 2.14 27 2.14 27.01 2.74 28.1 2.51 28.11 2.01 30 2.01 11 12 31.5 2.01 31.51 2.21 33.6 2.36 33.61 1.56 35 1.56 39.99 1.56 40 2.7 5 5.5 45 3.02 7 8 50 3.03 7.5 8 55 3.02 9 9.5 60 3.01 5 5.5 65 2.57 70 2.27 75 1.99 80 1.97 85 1.96 90 1.97 Lower sand Lower sand Peat/sand Refusal top bottom contact (cm) (cm) (cm) (cm) 70 70.5 104 147 67 67.5 110 145 76 78 107 148 88 91 132 150 79.5 81 90 150 45 45.1 70 87 46 80 55 57 68 120 57.5 58.5 76 147 57.5 60 90 154 58 59.5 88 190 61.5 62.5 90 175 37 39 79 117 10 13 40 110 105 105 105 100 84 Fair Harbour thickness matrix; 300 B P v. 1964 tsunami sand sheet thickness 3.5 1 1964 3 tsunami 2.5 1 thickness 2 3 1 1 (cm) 1.5 1 4 4 1 1 1 7 5 1 2 7 1 1 3 5 2 2 1 1 1 1 0.5 2 8 1 6 1 5 21 7 2 1 1 0 1 3 4 5 2 4 2 2 1 1 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 1 0 300BP tsunami thickness (cm) 85 FAIR HARBOUR GRAIN SIZE ANALYSIS SAMPLE # >1000|i >700LI >500LI >350|x FH MLB--27 0.05 0.25 0.45 0.9 FH MLB--25 0.6 2.9 3.85 4.3 -H MLB--22.5 0.5 0.8 1.1 1.35 FH MLB--20 0 0.05 0.2 0.35 -H MLB-16.2 0.15 0.8 1.9 2.8 FH MLO-0 0.1 0.2 0.8 1.95 FH MLO-5 0.1 0.25 0.55 1.35 FH MLO-10 0 0 0.1 0.4 FH MLO-15 0.05 0.15 0.75 1.75 FH MLO-20 0.05 0.15 0.3 0.65 FH MLO-25 0 0.1 0.25 0.55 FH MLO-30 0.25 0.45 1.35 2.8 FH MLO-35 0.35 1.7 4.2 5.55 FH MLO-40 0.5 4.9 7.85 8.65 FH MLO-45 1.2 5.3 1 0 10.8 FH MLO-50 FH MLO-55 0.5 2.65 3.5 4.1 FH MLO-60 0.15 0.3 0.35 0.4 FH MLO-65 0.15 0.35 0.55 1 FH MLO-70 0.25 0.55 1.3 2.15 FM MLO-75 0.25 0.35 0.65 0.95 FH MLO-80 0.05 0.15 0.5 1.3 FH MLO-85 0 0.2 1.1 2.7 FH MLO-90 0 0.2 0.85 2.15 FH L20-10 0.15 0.4 1.15 2.6 FH L15-10 0 0.2 0.65 1.2 FH L10-10 0.1 0.25 0.35 0.75 FH L05-10 0.05 0.25 0.45 1 FH MLO-10 0 0 0.1 0.4 FH R05-10 0 0.25 0.65 1.25 FH R10-10 0.15 0.2 0.35 0.55 FH R15-10 0.1 0.25 0.65 1.25 FH R20-10 0.15 0.25 0.25 0.55 FH R25-10 0 0.15 0.3 0.65 FH R30-10 0 0 0.1 0.35 >250LI >175LI >125|i. >88(x >62.5LI 1.35 2.7 5.35 8.85 10.5 4.8 5.75 6.85 8.05 8.8 1.5 2.4 3.4 4.15 4.5 0.65 1.7 3.25 4.6 5.15 4.1 5.9 7.1 7.6 7.9 3.35 5.05 6.2 6.85 7.05 2.7 4.9 7.1 8.35 8.75 1.25 2.5 3.6 4.2 4.4 2.95 5 6.9 8 8.4 1.1 1.85 2.85 3.2 3.45 1 1.95 3 3.85 4.2 4.5 6.75 8.85 10.15 10.5 7.1 8.6 9.65 10.2 10.3 9 9.1 9.1 9.1 9.1 11.05 11.1 11.1 11.1 11.1 5.1 7.15 8.9 9.7 9.85 0.7 1.5 2.3 2.6 2.6 1.75 3.1 4.15 4.55 4.75 3.7 5.85 7.15 7.6 7.65 1.2 1.6 2 2.25 2.4 2.25 3.65 4.75 5.35 5.65 4.65 6.95 8.15 8.5 8.6 4.05 6.95 8.9 9.45 9.55 4.25 6.5 8 8.7 9.05 2.05 3.3 4.5 5.15 5.45 1.6 3.05 4.4 5.1 5.3 2.05 4.1 6.2 7.55 8.05 1.25 2.5 3.6 4.2 4.4 2.1 3.75 5.9 7.4 7.95 1.05 2.2 3.7 4.75 5.3 2.25 4.15 6.75 8.5 9.25 1.35 3.05 5.05 6.6 7.25 1.3 2.75 4.45 5.35 5.85 1.45 3.65 6.4 8.05 8.2 86 APPENDIX 2 NEROUTSOS INLET DATA Neroutsos Inlet marsh is located at UTM coordinates 5576500N, 611250E. The road is in very good condition. Travel on Highway 19 to within about 25 km of Port Hardy and turn west onto the road to Port Alice. Continue past Port Alice about 5 km on an unpaved road until the marsh is first seen to the west. There is a campsite near a waterfall on the left side of the road across from a large turn out. A trail from the turn out leads to the old cabin site on the marsh (see Fig. 2.3B). 87 Neroutsos Inlet RO (ML), 0-16m, 1995 16m 10m 0m 3m 2m Peat Sand with some gravel — Tsunami sand sheet • End of hole Vertical exaggeration = 20x 88 Neroutsos Inlet R15, 0-22.5m, 1995 22.5m 1dm ~~Om Neroutsos Inlet R20, 0-31.5 m, 1995 31.5m 20m 10m ~~Om Neroutsos Inlet R25, 0-32.5 m, 1995 89 Neroutsos Inlet RO (ML), 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Refusal number edge elevation top bottom top bottom contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) 0 2.73 5 7 17 18 25 29 5 3.22 2 2.5 48 48.5 83 89 10 3.22 1.5 2 59 61 85 90 15 3.12 4 4.5 54 56 85 89 16 2.97 13 14 42 45.5 83 90 16.01 2.24 Neroutsos Inlet R5, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Refusal number edge elevation top bottom top bottom contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) 0 3.23 3 3.2 47 47.5 63 73 5 3.02 24 25 60 60 5.4 2.86 5.41 2.4 7.4 2.31 7.41 3.01 10 3.2 4 4.5 54 56 85 92 15 3.11 2 2.5 57 58 83 84 18.5 2.94 11 12 39 41 72 84 18.51 2.2 Neroutsos Inlet R10, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Refusal number edge elevation top bottom top bottom contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) 0 3.24 4 4.5 45 48 81 81 5 3.24 3.5 3.7 48 48.5 77 82 10 2.97 3 4 39 40 60 67 11 2.72 13 2.31 13.01 2.92 15 2.92 2 3 55 57 70 75 20 2.75 15 16 48.5 50 60 65 21.5 2.57 32 36 50 50 21.51 2.17 90 Neroutsos Inlet R15, 1995 Hole Bank Surface Upper sand Upper sand number edge elevation top bottom (m) (m) (LLW, m) (cm) (cm) 0 3.26 4.5 5 5 3.26 6 6.5 10 2.92 18 18.5 15 2.35 20 21 20 2.31 20.8 2.31 20.81 2.75 22.5 2.73 17.5 17.7 22.51 2.19 Neroutsos Inlet R20, 1995 Hole Bank Surface Upper sand Upper sand number edge elevation top bottom (m) (m) (LLW, m) (cm) (cm) 0 3.24 6 6.2 5 3.23 14 15 10 3.13 8.5 9 15 2.97 2.5 3 20 2.92 10.5 11 25 2.92 9 9.2 30 2.59 3 5 31.5 2.42 9 11 31.51 2.16 Neroutsos Inlet R25, 1995 Hole Bank Surface Upper sand Upper sand number edge elevation top bottom (m) (m) (LLW, m) (cm) (cm) 0 3.21 5 5.5 5 3.24 7 7.2 10 3.24 8 8.2 15 3.09 10 10.5 20 3.03 9.5 10 25 2.76 10 12 30 2.52 4 5 32.5 2.47 3 4 32.51 2.19 Lower sand Lower sand Peat/sand Refusal top bottom contact (cm) (cm) (cm) (cm) 37 39 79 81 58 60.5 70 78 41 42.5 50 56 40 42 50 60 20 20 50 51.5 66 70 Lower sand Lower sand Peat/sand Refusal top bottom contact (cm) (cm) (cm) (cm) 46 50.5 76 76 50 51.5 75 78 48 50 70 72 52 54 65 65 53 54.5 79 92 32 34 80 80 32 34 40 40 ? ? 26 26 Lower sand Lower sand Peat/sand Refusal top bottom contact (cm) (cm) (cm) (cm) 43 44.5 71 71 56.5 58 78 78 59 60 80 80 42 44 70 73 46 47.5 80 85 35 38 56 56 ? ? 21 38 16 18 28 35 91 APPENDIX 3 KOPRINO HARBOUR DATA Koprino Harbour marsh is located at UTM coordinates 5595450N, 582750E. It is about 2 hours from the end of the pavement ends near Port Hardy. This rough road is a logging truck thoroughfare. Travel south from Port Hardy about 4 km and turn west on the road to Holdberg. Continue southeast from Holdberg until the road ends near the campground at Koprino Harbour. The marsh is reached by crossing the Koprino River bridge about 2 km before reaching the campground, and then turning onto the first skid road on the right. This road ends at a clearcut. During the summer of 1995 a trail was cleared and flagged to the marsh. The Koprino grid is also presented in Figure 2.3C. 92 CD > CO i _ CT) CO E o CO D E CD C -C CO i § CO C (0 0 CO T= Q. CO CTJ CD CD co c CO 0 w O I f (0 o CO X o CM o = QJ CO 0 O) CT) CO X CD U "CO o "•£ • 0 > 93 94 95 96 97 CD > ra i— CD CD E o co E CD C 'i— co E o <~ "a co c CD (0 , n 0. CO CD CD CD CO T 3 C CO CD CO o E ; CO o O C -o CO 3 £ co X o CM c o a) co CD CD CD CO X CD m 76 o • CD > 98 CO CD > •4—• CO CD CD pn he CU F w LUOS ine i and CD JZ v_ CO c/> O wit LUOj ami . c o o c San Gla Tsu En( X o CM c o 2 CD CD CD CO X o> "CO o 'tr CD > 99 100 Koprino Harbor ML-0,1995 Hole Bank Surface Upper sand Upper sand number edge elevation top bottom (m) (m) (LLW, m) (cm) (cm) 33 4.35 30 4.08 25 3.83 20 3.74 15 3.74 10 3.69 5 3.52 0 3.52 5 3.53 22 23 8 3.26 8.01 2.77 9.1 2.83 9.11 3.09 10 3.29 15 3.53 20 3.54 ? ? 25 3.39 26 28 30 3.7 ? ? 33 3.77 ? ? sand Lower sand Peat/sand Sand/mud End of hole top bottom contact contact (cm) (cm) (cm) (cm) (cm) 61 65 162 28 30 50 58 180 33 40 200 61 65 162 59 63 200 15.5 16 62 67 180 42 44 48 67 52 63 200 45 59 200 55 65 200 35 58 200 24 26 51 85 48 50 56 62 150 ? ? , 60 200 ? ? ? 76.5 140 101 Koprino Harbor ML-55, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Sand/mud End of hole number edge elevation top bottom top bottom contact contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) (cm) 30 27 26.5 3.63 3.44 3.2 50 54 200 25 24 23.99 3.06 3.06 3.46 0 10 200 20 3.43 54 57 200 15 3.47 52 60 200 9 3.45 7 7.2 56 64 190 5 3.33 7 7.2 50 58 200 0 3.35 54 60 200 5 5.3 5.31 3.37 3.33 2.64 9 10 70 80 200 10 10.5 10.51 2.71 2.69 3.34 7 7.5 72 82 250 15 3.54 ? 82 92 200 20 3.16 5 5.2 56 65 200 25 3.38 48 63 200 30 3.49 57 72 200 35 3.61 62 75 200 40 3.59 58 65 200 45 3.68 67 75 200 Koprino Harbor ML-100, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Sand/mud End of he number edge elevation top bottom top bottom contact contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) (cm) 37.5 3.74 40 50 200 35 3.53 53 62 90 30 3.33 38 47 1.3 25 3.12 45 55 160 20 3.45 46 52 200 15 3.36 5 5.2 57 69 200 10 3.26 7 8 45 55 200 5 3.4 5 5.2 57 69 200 0 3.42 4.5 4.7 41 41.5 61 75 200 5 3.48 5 5.5 42.5 43 73 86 200 10 3.39 7 7.2 30.5 31 68 80 200 15 3.38 7 7.5 ? ? 76 90 260 15.9 3.27 15.91 2.89 17.5 2.64 19.2 2.96 19.21 3.34 20 3.46 9 10 52 52.5 85 95 200 25 3.42 6 6.5 54 54.5 81 94 200 26 3.33 26.01 2.74 30 2.49 0 10 2000 33.2 2.62 33.21 3.22 35 3.4 6 7 70 82 183 40 3.71 38 40 66 90 175 103 Koprino Harbor ML-150, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Sand/mud End of h lumber edge elevation top bottom top bottom contact contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) (cm) 40 3.8 42 47 64 200 35.01 3.46 35 3.14 47 52 200 30 2.94 6 7 37 39 45 200 29.99 3.25 25 3.3 5 5.5 42 46 200 20 3.4 5 5.2 57 64 200 16 3.34 15.2 3.22 15.21 2.83 15 2.83 6 6.5 56 62 200 14.99 3.22 14 3.39 10.2 3.42 10.19 3.24 10 3.24 75 88 200 9.4 3.24 9.41 3.51 5 3.41 4 4.5 67 72 200 0 3.21 6 6.5 51 51.2 66 72 200 5 3.33 5 5.2 39 40 75 81 200 7.1 3.24 7.11 2.67 10 2.57 8 8.5 44 46 71 81 200 15 2.46 7.5 8 ? 7 72 95 170 16 2.49 16.01 3.14 20 3.44 7 7.5 48 50 90 112 200 25 3.36 6 6.2 60 80 200 30 3.26 5 5.2 31 31.5 48 62 200 34.8 3.19 35 2.8 6.5 7 41 52 240 35.2 3.19 40 3.47 5 5.2 62 70 200 45 3.23 4 4.5 47 56 193 50 3.65 61 82 170 104 Koprino Harbor ML-200, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Sand/mud End of h lumber edge elevation top bottom top bottom contact contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) (cm) 45 3.69 29 30 65 69 1.05 40 3.45 47 200 36.01 3.24 36 2.97 35 2.96 43 50 200 34.99 3.31 30 3.44 55 67 200 25 3.41 68 74 200 20 3.39 71 79 200 15 3.31 8 8.52 60 65 200 14.6 3.21 14.59 2.58 10 2.44 15 5.5 2.73 5.49 3.28 5 3.35 6 6.5 ? ? 85 97 200 0 3.3 6 7 63 64 94 5 3.32 6 7 56 56.5 93 6.1 3.28 6.11 2.77 7.9 2.71 7.91 3.18 9.4 3.24 10 2.52 6 7.5 52 52.5 80 15 2.54 10 20 200 17.7 2.73 17.71 3.1 19.7 3.24 19.71 2.95 20 3.08 6 8 39 39.2 71 20.8 2.94 20.81 3.23 25 3.35 6 7.5 60 60.2 79 85 183 27.6 3.21 27.61 2.77 28.7 2.77 28.71 3.13 30 3.29 6 7.5 49.5 51 64 70 200 35 3.36 5 5.5 50 54 62 73 170 40 3.33 5 5.5 66 42 3.19 42.01 2.79 44.6 2.77 44.61 3.13 45 3.24 6.5 8 46 58 100 50 3.42 6 7 57 57.2 65 69 200 55 3.47 5 5.5 55 55.2 62 69 200 60 3.54 6 6.5 51 51.5 60 65 3.59 65 70 3.67 64 64.5 67 75 3.6 39 40.5 50 56 200 80 3.6 45 52 200 85 3.79 42 53 180 105 Koprino Harbor ML-250, 1995 Hole Bank Surface Upper sand Upper sand Lower sand number edge elevation top bottom top (m) (m) (LLW, m) (cm) (cm) (cm) 90 - 3.96 23 30 2.63 25.01 2.64 25 3.13 7 8 20 3.1 53 18.31 2.99 18.3 2.63 15 2.39 10 2.41 5 2.43 0 2.68 7 7.5 37.5 1 2.68 1.01 3.18 3.5 3.16 3.51 2.74 5 2.82 6.5 8 5.01 3.2 8.3 3.19 8.31 2.78 10 2.65 7.5 9 38 11.4 2.7 11.41 3.17 14 3.15 14.01 2.73 15 2.75 7 8 39 15.01 3.16 17 3.11 17.01 2.72 19.1 2.72 19.11 3.15 20 3.23 5.5 6.5 36 21.3 3.07 21.31 2.72 22.5 2.7 22.51 3.06 23.6 3.15 23.61 2.68 25 2.66 5.5 6.5 38 26.8 2.68 , 26.81 3.15 30 3.23 5 6 35 3.31 6 7 40 3.21 5 5.5 40.01 2.72 41.4 2.71 41.41 3.17 45 3.38 5 6 49.4 3.22 49.41 2.75 49.99 2.76 50 3.17 5 6 37? 55 3.38 5 5.5 60 3.28 Lower sand Peat/sand Sand/mud End of hole bottom contact contact (cm) (cm) (cm) (cm) 34 51 180 0 20 200 57 70 200 55 63 81 200 0 25 200 15 5 38 38.5 39.5 36.5 38.5 60 85 106 Koprino Harbor ML-250, 1995 (Continued) Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Sand/mud End of hole number edge elevation top bottom top bottom contact contact (m) (m) 64.5 64.51 (LLW, m) 3.23 2.77 (cm) (cm) (cm) (cm) (cm) (cm) (cm) 65 65.01 2.79 3.25 7 8 75 88 200 70 3.58 70 75 3.48 5 5.2 57 64 200 80 3.32 5 6 39 45 200 85 3.56 47 53 95 89 3.86 41 44 61 200 107 Koprino Harbor ML-300, 1995 End of hole (cm) 200 200 200 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Sand/mud number edge elevation top bottom top bottom contact contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) 0 3.1 8.5 9 34 35.5 57 75 4.99 3.16 5 2.61 6.5 7.5 35 35.5 70 95 10 2.57 7 7.5 38 38.2 59 105 10.6 3.04 12.5 2.65 12.51 3.03 15 3.3 7 8 68 20 3.31 5 5.5 74 20.3 3.2 20.31 2.64 25 2.66 6 6.5 60 70 25.1 3.1 29.99 3.2 30 2.66 7 8 78 110 35 2.66 6 7 68 35.01 3.23 38 2.7 38.01 3.13 40 3.33 6 6.5 70 43.5 3.23 43.51 2.73 45 2.71 5 6 61 95 46 2.73 46.01 3.34 50 3.54 75 55 3.69 61 80 60 3.75 49 54 95 65 3.82 56 61 100 69 3.53 59 65 85 108 Koprino Harbor ML, 1995 Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Sand/mud End of hole number edge elevation top bottom top bottom contact contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) (cm) 25 3.42 25 40 90 20.5 3.35 20 3.11 8 120 19.5 3.01 17 2.96 16.99 3.26 15 3.42 30 49 200 10 3.2 30 41 90 5 3.52 48 58 200 0 3.52 5 3.52 52 61 200 10 3.52 58 65 200 15 3.51 57 65 200 20 3.35 46 50 82 25 3.36 8 8.2 52 61 150 30 3.38 52 58 170 33.2 3.4 33.21 2.81 34.09 2.77 34.1 3.49 35 3.46 5 5.2 66 75 200 40 3.32 10 10.5 61 68 200 45 3.42 7 9 63 75 175 48 3.29 48.01 2.66 49.7 2.72 49.71 3.26 50 3.39 61 74 200 55 3.35 57.5 3.29 57.51 2.77 58.6 2.92 58.61 3.22 60 3.42 5.5 6 63 72 200 65 3.34 59 64 180 70 2.83 54 61 105 70.01 3.21 75 3.4 5 5.1 51 51.5 55 72 200 75.7 3.29 75.71 2.81 76.7 2.81 76.71 3.22 80 3.29 7 7.5 . 42 55 100 85 3.42 57 74 200 90 3.43 5 5.1 56 67 200 92.6 3.41 92.61 2.93 94.6 2.78 94.61 3.22 95 3.32 100 3.42 105 3.43 5.5 5.52 59 73 120 109.5 3.3 Koprino Harbor ML, 1995 (Continued) Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Sand/mud End of hole umber edge elevation top bottom top bottom contact contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) (cm) 109.51 2.89 110 2.84 7.5 8 60 72 200 110.3 2.86 110.31 3.34 115 3.39 5.5 6 64 74 200 116.4 3.25 116.41 2.74 117.8 2.78 117.81 3.4 120 3.38 7 7.2 64 70 200 125 3.26 7 7.5 53 58 200 130 3.31 6 6.2 39 40 49 61 200 135 3.31 7 7.2 ? ? 55 65 200 136.5 3.2 136.51 2.64 138.5 2.66 138.51 3.22 140 3.39 57.5 58 72 80 200 144.2 3.26 144.21 2.84 145 2.8 5 5.2 43.5 44 57 71 200 145.01 3.24 150 3.21 6 6.5 ? ? 155 3.25 6 6.5 49 50 75 78 200 55.4 3.23 55.41 2.76 160 2.49 5 17 200 165 2.54 5 21 200 170 2.59 8 8.5 7 ? 85 97 200 170.4 2.62 170.41 3.21 175 3.34 5 5.5 53 54 84 111 200 179.7 3.23 179.71 2.88 180 2.84 7.5 8 63 64.5 77 88 200 180.6 2.85 180.61 3.23 185 3.43 5.5 6 74 75 100 130 200 190 3.38 12 12.5 64 64.5 95 117 200 195 3.27 5.5 6 70 72 79 95 95 200 3.3 6 7 63 64 77 94 94 205 3.35 5 5.5 66 67.5 89 100 100 206.3 3.16 206.31 2.61 210 2.55 22 22 215 2.55 ? ? ? ? 38 45 45 215.5 2.67 215.51 2.87 219.5 3 219.51 2.75 220 2.75 ? ? ? ? 48 60 60 220.4 2.75 110 Koprino Harbor ML, 1995 (Continued) Hole Bank Surface Upper sand Upper sand Lower sand Lower sand Peat/sand Sand/mud End of hole number edge elevation top bottom top bottom contact contact (m) (m) (LLW, m) (cm) (cm) (cm) (cm) (cm) (cm) (cm) 220.41 3.03 224.2 2.99 224.21 2.75 225 2.58 ? ? ? ? 60 60 228 2.69 230 3.27 57 58 80 80 232.6 3.06 232.61 2.67 235 2.58 25 25 240 2.42 8 8 245 2.38 5 5 250 2.68 7 7.5 37.5 38 87 87 252.3 2.68 252.31 3.08 255 3.18 6.5 7.5 ? ? 80 80 260 3.2 6 7 70 70 260.2 3.09 260.21 2.74 264 2.66 264.01 3.15 265 3.18 7 8 35 35.5 0.75 75 269.6 3.12 269.61 2.69 270 2.67 6 7 57 57 270.3 2.65 280 2.63 20 20 282.7 2.67 282.71 3.1 285 3.06 7 7.5 21 ? 68 68 285.6 3.04 285.61 2.67 289.99 2.68 290 3.09 8 9 40 41 60 70 70 294.99 3.07 295 2.6 8 9 37 37.5 63 81 81 299.5 2.58 299.51 3.07 300 3.1 111 Koprino Harbour thickness matrix; 300 B P v. 1964 tsunami sand sheet thickness 3.5 1964 3 tsunami 2.5 thickness 2 2 1 (cm) 1.5 3 2 1 1 23 9 3 1 0.5 32 6 3 4 3 1 0 1 4 1 0 4 1 5 0 0.5 1 1.5 2 2.5 3 3.5 4 300BP tsunami thickness (cm) 112 

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