Hybrid non-invasive characterization of soil strata at sites with and without embedded lava rock layers in the South Iceland Seismic Zone

The geological setting of Iceland is unusual, with highly jointed rock mass, loose sediments created in glacial outburst floods and eruptions, and layers of lava rock embedded in or overlying soft sediments. This study aims to assess the feasibility of a composite analysis of dispersion and ellipticity curves for characterization of two of the primary classes of soil sites in the South Iceland Seismic Zone. Specifically, it seeks to develop a cost-effective workflow to identify and characterize sites where a layer of lava rock is embedded in the sedimentary stratum at shallow depth, along with deep soil site characterization. Microtremor HVSR (horizontal-to-vertical spectral ratio) is found to be efficient to distinguish between sedimentary sites with and without an embedded lava rock layer. The results further demonstrate the effectiveness of hybrid ellipticity and dispersion curve inversion to characterize soil sites with an embedded layer of lava rock, which results in a strong velocity reversal with depth. Consistent with previous studies, the hybrid dispersion-ellipticity inversion is also found efficient for characterization of sites with a simpler structure.