Waveform inversion for lateral heterogeneities using multimode surface waves

Abstract

Summary We propose a waveform inversion scheme that can be used to invert strong structural heterogeneities. The method is based on a ray approximation for surface waves. Strong structural lateral variations are modelled by vertical discontinuities. Therefore, a geologically heterogeneous region is partitioned into a number of lateral homogeneous subregions. Synthetic seismograms are calculated by modal summation over incident and transmitted modes. With this method the complete waveforms of surface waves, including mode cross‐branch coupling, multipathing and scattering, are considered in the inversion. We test the method with several geophysically realistic structural models. An example of waveform inversion for real data—a wave path across the Iberian peninsula and the oceanic structure off the French coast owing to the Gibraltar earthquake (Ms= 5.7)—is presented. The method allows us to obtain the information represented by different set of structures along the same source–receiver minor arc through which the waves have propagated. The method is applicable to different models of lateral heterogeneity. In its present development, it is most appropriate for inverting structures around tectonic scenarios such as continental margins, grabens and discontinuities between major plates.

Surface Waves in Laterally Heterogeneous Media

“…Clearly, in geophysical imaging, numerical modeling of elastic waves has become popular in the last two decades or so (Virieux et al 2011). However, analytical approaches are still valuable for fast computations of the wave propagation when the source is far from the investigated region (see, for example, Panza et al 2001) or in some full waveform inversion methods (see, for example, Du 2002).…”

Feasibility of waveform inversion of Rayleigh waves for shallow shear-wave velocity using a genetic algorithm

“…Snieder (1988) proposed a large-scale waveform inversion scheme of surface waves using the surface scattering theory but with the assumption that lateral heterogeneity is smooth (Snieder and Nolet, 1987). Du (2002) used a ray theory approximation for surface waves originally developed by Levshin (1985) to invert multimode surface waves for tectonic structures such as continent-ocean boundaries. However, this method is not appropriate for near-surface studies due to the target is usually small compared to the wavelength of seismic waves.…”