Ambient vibration measurements in the Southern Rhine Graben close to Basle

A. Köhler, M. Ohrnberger, F. Scherbaum, S. Stange, F. Kind

Abstract


This study presents results of ambient noise measurements from temporary single station and small-scale array
deployments in the northeast of Basle. H/V spectral ratios were determined along various profiles crossing the
eastern masterfault of the Rhine Rift Valley and the adjacent sedimentary rift fills. The fundamental H/V peak
frequencies are decreasing along the profile towards the eastern direction being consistent with the dip of the tertiary
sediments within the rift. Using existing empirical relationships between H/V frequency peaks and the
depth of the dominant seismic contrast, derived on basis of the ?/4-resonance hypothesis and a power law depth
dependence of the S-wave velocity, we obtain thicknesses of the rift fill from about 155 m in the west to 280 m
in the east. This is in agreement with previous studies. The array analysis of the ambient noise wavefield yielded
a stable dispersion relation consistent with Rayleigh wave propagation velocities. We conclude that a significant
amount of surface waves is contained in the observed wavefield. The computed ellipticity for fundamental
mode Rayleigh waves for the velocity depth models used for the estimation of the sediment thicknesses is in
agreement with the observed H/V spectra over a large frequency band.

Keywords


H/V ratio;ambient vibration;array analysis;fundamental frequency;Rhine Rift Valley

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References


DOI: https://doi.org/10.4401/ag-3374
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X