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Regional characterization of large landslides in southwest Yukon, with emphasis on the role of neotectonics Everard, Keith Alan


Neotectonics may be defined as any recent movement or deformation at or near the earth's surface, and the associated geological processes or mechanisms thereof (Vita-Finzi 1986). A regional study of large landslides was undertaken in southwest Yukon, with the aim of assessing the relationship between large landslides and neotectonic processes, with particular emphasis on the role of seismicity. Landslides were inventoried in an area covering 18,800 km² in southwest Yukon and 4,400 km² in adjacent south-eastern Alaska. Their spatial distribution was found to correlate with certain lithological units, regional faults, and often dense clusters of low-level earthquakes. Seismicity is especially intense in the Cement Creek area, where the relative temporal distribution of landslides departs from the regional slope exhaustion model and more closely resembles a steady-state distribution. A recent (1983) landslide in this area was attributed to a modest M5.4 earthquake (Power 1988). Field reconnaissance in Cement Creek valley was undertaken to assess the possible role of neotectonic processes, and to gather data for a program of numerical modelling. Rupture surfaces of the landslides were generally coincident with bedding surfaces in the tightly folded volcanic rocks. Geomorphic evidence suggests an incremental displacement failure mechanism. The available methods of dynamic numerical modelling are reviewed. Program UDEC is found to be an appropriate analytical package for the modelling program. Limited verification tests of UDEC were performed. Strong motion data from a magnitude 4.6 earthquake were input successively to a representative slope model. The program was able to simulate geomorphic features related to slope deformation at Cement Creek, as well as confirming seismicity as a possible landslide triggering mechanism.

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