Ultrahigh-resolution shear-wave reflection imaging of vertical-component data in a quick-clay prone to landslide area in southwest Sweden

Abstract

We have investigated the potential of ultrahigh-resolution seismic reflection imaging of vertical-component data to identify hazardous conditions in a quick-clay landslide area in southwest Sweden. A high-fold survey with a fine shot and receiver spacing has been acquired using a 5 kg sledgehammer, vertical hit, with the objective of producing a high-quality unaliased shear-wave reflection section retrieved from vertical-component data. On the receiver side, 1C wireless recorders are deployed in a fixed geometry juxtaposed to a landstreamer of 3C-microelectro mechanical system (MEMS)-based units, which recorded in a roll strategy to cover most of the profile length. Particle motion analysis of main reflections has been conducted on the 3C MEMS sensors, given their side-by-side location with the wireless recorders, to inspect the wave polarization. Distinct shear-wave reflections in an extremely slow shear velocity medium (70–100 m/s) imply a vertical super resolution of 1–2 m down to a bedrock level of 40 m deep. Interestingly and as shown in earlier studies, quick clays appear to overlie the coarse-grained horizons justifying why their high-resolution imaging can be significant for quick-clay landslide studies and a better understanding of potential risks. Two shallow reflections are delineated through a combination of first-break traveltime tomography for P and S waves and reflection seismic processing for P- and S-reflections of the vertical-component data. After seismic imaging and borehole data correlation, the shallowest reflection is interpreted to be from coarse-grained materials interbedded within normally consolidated clays and the deepest one from an undulating bedrock. Interpretations of the S-S processing outcomes indicate that the coarse-grained layers are not homogeneous because of the generation of strong shear-wave diffractions, suggesting the presence of either large boulders or patchy sandy-silty conditions.