Near-surface 2D SH-waveform Inversion - A Case Study from Slovakia

Abstract

We apply elastic time-domain 2D full waveform inversion (FWI) to a near surface SH-wave data set recorded in the village Cachtice in northwestern Slovakia. Aim of the seismic survey was the detection of possible basement structures. The recorded data, consisting of 42 shots and receivers distributed along a 21 m long profile, covers a wide frequency range from 5 Hz to 100 Hz with high signal-to-noise ratio well suited for FWI. In addition to the direct SH/Love-wave a distinct refracted wave is visible. The trend of the first arrivals suggests an approximately 1D velocity gradient in the subsurface. Therefore a 1D initial model for the FWI is estimated by the Wiechert-Herglotz method. For the initial density model a similar gradient medium is assumed. The 2D FWI is based on the global correlation norm as objective function in combination with sequential frequency inversion. The final FWI S-wave velocity and density models reveal a heterogeneous underground with a prominent low-velocity weathering layer and isolated high-velocity anomalies. The structures of the density model correlate well with the velocity model.