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UBC Theses and Dissertations

Structure of the Eastern Coast Belt, southwestern Canadian Cordillera, from reproducing lithoprobe seismic reflection lines 88-17 and 88-14 Zhang, Weimin


As part of the Lithoprobe Southern Cordillera research program, seismic reflection data were acquired in 1988 along a 100 km profile across the Eastern and Central Coast Belts (lines 88-14 and 88-17) in a region of complex surface geology. A very good interpretation of the crustal section based on previous processing by industry has been made. However, the data were not processed specifically to enhance the features in the upper 5 s and provide a clear tie to surface geology, some of which is newly studied since the earlier interpretation. The present study involves reprocessing of these data to provide this enhancement. Severe crookedness of the line necessitated the implementation of unconventional processing techniques, including creation of several mini-profiles which cut through the midpoint scatter and application of a first-order correction for effects of reflector crossdip ( i.e., the crossline component of reflector dip). Refraction-based statics were computed using a two-step procedure consisting of initial identification and correction of systematic errors in the picked first break traveltimes, and subsequent application of a 2-D statics algorithm. Dip moveout (DMO) was applied to constant-offset gathers to effect prestack partial migration and reduce the dependence of normal moveout velocity on reflector dip. To reduce possible smearing in the upper few seconds, stacks were repeated with truncated spread lengths. The Karhunen-Loeve transform was applied efficiently and economically on the stacked seismic data to enhance coherent signals in all selected dips. The reprocessing has better delineated the subsurface geometry of the terranes and faults and expressed some of the structures which are not visible on previous processing sections, even though the 2-D seismic images cannot completely express the 3-D complexity inferred from the surface geology. The reprocessed sections are considered in light of the new geological mapping to provide a refined interpretation of subsurface structure and its implication for local tectonics. A new geological model is developed based on this refined interpretation and is being further tested by seismic forward modeling.

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