Abstract
Geophysical site investigations have been performed in association with deployment of a dense array of 95 3-component seismometers on the Cavola landslide in the Northern Apennines. The aim of the array is to study propagation of seismic waves in the heterogeneous medium through comparison of observation and modelling. The small-aperture array (130 m×56 m) operated continuously for three months in 2004. Cavola landslide consists of a clay body sliding over mudstone-shale basement, and has a record of historical activity, including destruction of a small village in 1960. The site investigations include down-hole logging of P- and S-wave travel times at a new borehole drilled within the array, two seismic refraction lines with both P-wave profiling and surface-wave analyses, geo-electrical profiles and seismic noise measurements. From the different approaches a consistent picture of the depths and seismic velocities for the landslide has emerged. Their estimates agree with resonance frequencies of seismic noise, and also with the logged depths to basement of 25 m at a new borehole and of 44 m at a pre-existing borehole. Velocities for S waves increase with depth, from 230 m/s at the surface to 625 m/s in basement immediately below the landslide.
Highlights
Several towns in the Northern Apennines are located on detrital cover, such as alluvial sediments or slope debris, and because of the region’s geological history, the area has an intrinsic proneness to landslides
The Cavola landslide is derived from marly-calcareous flysch of the Monghidoro Formation (Upper Maastrichtian-Lower Paleocene) and Monte Venere Formation (Upper Campanian-Maastrichtian), both belonging to Ligurian Units, outcropping to the south of Cavola village (Plesi, 2002)
They are characterized by a large crown, a narrow channel and large foot and the Cavola landslide is a good example of such a morphology
Summary
Several towns in the Northern Apennines are located on detrital cover, such as alluvial sediments or slope debris, and because of the region’s geological history, the area has an intrinsic proneness to landslides. The high content of clay minerals and their propensity for absorbing water facilitates the formation and triggering of landslides. Coupled with this inherent instability, the region has moderate but continuous seismicity. The presence of heterogeneity required a dense station spacing to quantify variation of site response over short distances. The first step towards studying the seismic wave propagation is the reconstruction of the landslide body, in terms of geometry and wave velocities. In this preliminary paper we focus on this goal achieved using a multidisciplinary approach based on geological, geophysical and seismic investigations. We had the benefit of an existing borehole in the array area, and a second stratigraphic borehole was added, including P- and S-wave travel time logging
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