3-D time-domain Gauss–Newton full waveform inversion for near-surface site characterization

Abstract

We present a new 3-D time-domain Gauss–Newton full waveform inversion (3-D FWI) method for near-surface site characterization. The method is based on a solution of 3-D elastic wave equations for forward modelling of wave propagation, and Gauss–Newton inversion approach for model updating to extract material property. Both the forward modelling and model updating are conducted in the time domain, which allows exploiting complete waveform information of multiple frequencies simultaneously for detailed subsurface material properties. Based on virtual sources and reciprocal wavefields, an efficient approach is developed to calculate derivative seismograms (Jacobian matrix) for all cells simultaneously. The capability of the presented FWI method is tested on both synthetic and field experimental data sets. Sensors and sources located in uniform 2-D grids on the ground surface are used to acquire seismic wavefields, which are then inverted for extraction of 3-D subsurface wave velocity structures. The results show that the waveform analysis was able to characterize low- and high-velocity synthetic layers, and variable soil/rock layers of the test site. The S-wave velocity (Vs) profiles from field experiment generally agree with invasive standard penetration test (SPT) N-values, including identification of a low-velocity zone. Vs profiles obtained from a cross-adjoint 3-D FWI are also included for comparison, and results from the presented Gauss–Newton inversion are more consistent with the SPT N-values in both trend and magnitudes.