Waveform Tomography of Land Data from a Complex Thrust-Fold Belt in Western Canada: What Works, What Doesn’t, and What Needs to Improve

Abstract

In the Canadian Foothills, long-offset seismic data are occasionally acquired in an effort to "undershoot" areas of steeply dipping faults and a severely weathered near-surface. Since long-offsets are one method of acquiring the low-wavenumber information necessary for Waveform Tomography (diving wave tomography followed by full-waveform inversion), these data provide an excellent opportunity for demonstrating the efficacy of the method in building velocity models in with land seismic data, in areas possessing large, lateral velocity variations. However, the acquisition of lowfrequency field data remains a challenge: the majority of land-seismic field crews use 10Hz geophones. The use of MEMS accelerometers (with a broadband response in the acceleration domain) was proposed as a solution to this problem, but the results of a recent high-effort, long-offset acquisition demonstrate that the records possess sub-optimal low-frequency data, dominated by instrument noise. In addition, full-waveform inversion of land seismic data must account for the effects of elastic modes such as ground roll. Without an efficient, multi-parameter, elastic inversion scheme, we must use one based upon the acoustic wave-equation, and care must be taken to mitigate the effects of elastic modes<br>during pre-processing of the seismic data. If seismic data are recorded with an appropriately designed acquisition (i.e., long-offsets and recording instruments capable of recording the low-frequencies), and sufficient, appropriate preprocessing is applied to the input data, acoustic full-waveform inversion can produce complex velocity models of the sub-surface from field seismic data acquired on land in complex geological settings.