On the applicability of 2D SH-FWI for high-resolution imaging of 3D subsurface structures

Summary Seismic full waveform inversion (FWI) has been established as a tool for the characterization of near-surface structures in a wide-range of applications from engineering/archaeogeophysics to hydrocarbon exploration. To reduce computational costs, most FWI applications are using 2D medium approximations to describe seismic wave propagation in the framework of the inverse problem, even if the subsurface structures would demand a 3D medium description. In this study, we investigate the applicability of a 2D SH-FWI to map complex, 3D subsurface structures of a potential thrust fault system, located east of the Great Plon lake in Northern Germany. During two extensive, geophysical field surveys in 2017/2018, four intersecting, seismic SH-profiles were acquired, covering the study area. The independent FWI of the SH-profiles with respect to the shear-wave velocity and density model reveals complex, heterogeneous subsurface structures. Despite the simplified 2D medium approximations used in the FWI, similar features are visible at the intersection points of the SH-profiles. The near-surface area down to a depth of 15 m is dominated by thin, alternating, layers disturbed by low-velocity anomalies. The deeper subsurface consists of high-velocity anomalies dipping in SW direction. The general trends of FWI density models can be correlated with borehole density logs.