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

University of British Columbia

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.

Thesis/Dissertation

application/pdf

2008-09-17

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http://hdl.handle.net/2429/2172

Geophysics

University of British Columbia

UBCV

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