We investigated the potential of ultra-high-resolution seismic reflection imaging of vertical component data to identify hazardous conditions in a quick-clay landslide area in southwest of Sweden. A high fold survey with a fine shot and receiver spacing was acquired using a 5-kg sledgehammer, vertical hit, with the objective of producing high quality unaliased shear-wave reflection section retrieved from vertical component data. On the receiver side, 1C wireless recorders were deployed in a fixed geometry juxtaposed to a landstreamer of 3C-MEMS-based units, which recorded in a roll strategy to cover most of the profile length. Particle motion analysis of main reflections was 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) implied 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 better understanding of potential risks. Two shallow reflections were 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 was 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 in this work propose 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.
A prototype electromagnetic vibrator, referred to here as E‐Vib, was upgraded and developed for broadband hardrock and mineral exploration seismic surveys. We selected the iron oxide mine in Blötberget, central Sweden, for a test site in 2019 for the newly developed E‐Vib because of the availability of earlier seismic datasets (from 2015 to 2016) for verification of its performance for hardrock imaging purposes. The two‐dimensional data acquisition consisted of a fixed geometry with 550 receiver locations spaced at every 5 m, employing both cabled and wireless seismic recorders, along an approximately 2.7 km long profile. The E‐Vib operated at every second receiver station (i.e. 10 m spacing) with a linear sweep of 2–180 Hz and with a peak force of 7 kN. The processing workflow took advantage of the broadband signal generated by the E‐Vib in this challenging hardrock environment with varying ground conditions. The processed seismic section shows a set of reflections associated with the known iron oxide mineralization and a major crosscutting reflection interpreted to be from a fault system likely to be crosscutting the mineralization. The broadband source data acquisition and subsequent processing helped to improve signal quality and resolution in comparison with the earlier workflows and data where a drophammer seismic source was used as the seismic source. These results suggest new possibilities for the E‐Vib source for improved targeting in hardrock geological settings.
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