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UBC Theses and Dissertations

Characterization of the Fraser fault, Southwestern British Columbia, and surrounding geology through reprocessing of seismic reflection data Perz, Michael J.


Seismic reflection data were acquired in 1988 along a 70 km profile crossing the Fraser fault, a major dextral strike-slip boundary between the Eastern Coast and Inter-montane belts of the southern Canadian Cordillera. Preliminary processing by industry contract and subsequent interpretation revealed several interesting tectonic features; however, the subsurface position and depth extent of the fault were ambiguous. The present study involves reprocessing of these data in an effort to provide an improved subsurface image, and hence a better understanding of the local tectonic regime. Severe crookedness of the line necessitated the implementation of unconventional processing techniques, including creation of several "mini-profiles" which cut through the scatter of source-receiver midpoints near the fault zone, and application of a first-order correction for effects of reflector crossdip (i.e., the crossline component of reflector dip). A method for estimating the optimum crossdip correction parameter was developed. Although it demonstrated promise when applied to synthetic data, disappointing results were obtained with the field data. Refraction-based statics were computed using a two-step procedure consisting of initial identification and correction of systematic errors in the picked first break travel times, and subsequent application of a conventional 2—D statics algorithm. Dip move out correction (DMO) was applied to the upper 5.0 s of data to enhance the image of steeply dipping features. Significant aspects of the interpretation of the reprocessed dataset include: (i) evidence of deep crustal extent (or possible crustal penetration) for the Fraser fault; (ii) correlation of two northeast-dipping reflectors (not visible on the contract-processed sections) with southwest-directed thrusting along the Pasayten fault; and (iii) correlation of two east-dipping events near the western edge of the profile with deep roots of the Coast Belt Thrust System.

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