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Developments in waveform tomography of land seismic data with applications in south-central British Columbia

University of British Columbia

Waveform tomography (WT) is an advanced class of seismic imaging methods that may be applied to generate detailed models of subsurface velocity and attenuation by analysis of recorded field seismograms. WT comprises two steps: 1) initial velocity model building by traveltime inversion (raytracing) and 2) full-waveform inversion to update the model of velocity based on analysis of refracted data waveforms. The nature of this method requires that the initial model and simulated survey parameters reproduce closely those used for the field data acquisition. The application of WT to on-land seismic data is challenged by the geometry irregularities inherent in crooked-line two-dimensional (2D) seismic data acquisition. This thesis develops two methodologies that permit the inversion of on-land crooked-line vibroseis multi-channel seismic (MCS) reflection data by traveltime tomography (TT) and subsequent viscoacoustic full-waveform inversion (FWI) to generate 2D cross sections of P-wave velocity. The first method uses 2.5D TT and applies a TT-derived static correction to enable the subsequent application of 2D FWI. The second method uses 2.5D or three-dimensional (3D) TT followed by 2.5D full-waveform inversion that models 3D survey geometry (a new development). These technical developments are motivated and tested by a multi-part case study, which analyses data from the 2008 Geoscience BC Nechako Basin seismic survey. Both the static-correction method and 2.5D FWI method are applied to a single acquisition line. The results are analysed and compared with the conclusion that 2.5D WT provides a superior result, but at additional computational cost. This cost is still significantly lower than that associated with 3D FWI. The 2.5D WT method is applied to three datasets from the 2008 survey, and TT alone is applied to a fourth. The resulting models constrain the positions and lithology of Eocene volcanic rock units, Cretaceous strata and Jurassic or earlier basement rocks in the Nechako-Chilcotin Plateau region of south-central British Columbia. These results are synthesized and interpreted in conjunction with colocated surficial-geology maps, exploration well logs and geophysical results by other workers. This interpretation enhances the specific knowledge of lithostratigraphy along these acquisition profiles and informs general geological and geophysical analyses of the region.

Text

2013-10-08

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/45219

Geophysics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/