Acoustic full-waveform inversion on land surveys: A case study on the Qademah fault, Saudi Arabia

Abstract

Geophysical methods have been used to map a Qademah fault near a residential area in western Saudi Arabia. However, the location and spatial extension of the fault zone are still uncertain due to the limited resolution and length of geophysical surveys. We apply seismic full-waveform inversion (FWI) to a land survey 2 km in length, the result of which reveals more details of the fault as well as the subsurface. Before inversion, we remove the surface waves, converted waves, and other elastic phenomena in the f- k domain and normalize the trace amplitude to compensate for attenuation, such that wavefield modeling for FWI can be approximated by acoustic propagators with constant density. Due to the large wavefield amplitudes near the source-receiver positions, the FWI velocity gradient presents a singular zone in the near surface, which is muted to stabilize the inversion. We also invert the short-offset traces before the larger-offset traces to avoid cycle skipping at the far offsets and obtain a reasonable data fit despite some mismatches in the near offsets. The final FWI velocity model shows the Qademah fault at approximately 1000 m distance as well as three low-velocity anomalies at 100 m depth, confirmed by first-arrival traveltime tomography. We also observe a potential low-velocity layer at 250–300 m depth, which was not reported in former studies. This model can also be used for geologic interpretation, hazard assessment, and paleoseismology studies of the local area.