Detection of a shallow-buried rock obstruction using 2D full waveform inversion

Abstract

Shallow-buried rock mass/obstructions in a reclaimed sand site have seriously delayed a construction project in eastern Singapore, and seismic surveys were conducted to estimate the location and range of the rock. Active-source and passive-source seismic data were recorded using an array with 24 geophones at 1 m intervals. A 2D full waveform inversion (FWI) approach, multichannel analysis of surface waves (MASW), and cross-correlation seismic interferometry were used to process the collected seismic data. Results show that MASW and cross-correlation provide useful information, but limited to 1D S-wave velocity profiles and the upper surface of shallow buried rock. Using the full information of seismic waveform, the FWI approach can reflect even the range of rock. Sequential inversion with a low-pass frequency filter at incremental corner frequencies can increase the precision of the FWI approach. With higher precision, the FWI of surface waves is considered to be an attractive and effective method to detect underground obstruction.