Reference soil condition for intensity prediction equations derived from seismological and geophysical data at seismic stations
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Date
2021-02
Publication Type
Journal Article
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yes
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Abstract
In 2011, an amplification map achieved by macroseismic information was developed for Switzerland using the collection of macroseismic intensity observations of past earthquakes. For each village, a Delta Imwas first derived, which reflects the difference between observed and expected macroseismic intensities from a region-specific intensity prediction equation. The Delta Imvalues are then grouped into geological/tectonic classes, which are then presented in the macroseismic amplification map. Both, the intensity prediction equation and the macroseismic amplification map are referenced to the same reference soil condition which so far was only roughly estimated. This reference soil condition is assessed in this contribution using geophysical and seismological data collected by the Swiss Seismological Service. Geophysical data consist of shear-wave velocity profiles measured at the seismic stations and earthquake recordings, used to retrieve empirical amplification functions at the sensor locations. Amplification functions are referenced to a generic rock profile (Swiss reference rock condition) that is well defined, and it is used for the national seismic hazard maps. Macroseismic amplification factorsAf, derived from empirical amplification functions, are assigned to each seismic station using ground motion to intensity conversions. We then assess the factorsd Delta fdefined as the difference betweenAfand Delta Im. The factord Delta faccounts for the difference between the reference soil condition for the intensity prediction equation and the Swiss reference rock. We finally analysed relationships betweenAfand proxies for shear-wave velocity profiles in terms of average shear-wave velocity over defined depth ranges, such asV(S,30), providing an estimate of the reference shear velocity for the intensity prediction equation and macroseismic amplification map. This study allows linking macroseismic intensity observations with experimental geophysical data, highlighting a good correspondence within the uncertainty range of macroseismic observations. However, statistical significance tests point out that the seismic stations are not evenly distributed among the various geological-tectonic classes of the macroseismic amplification map and its revision could be planned merging classes with similar behaviour or by defining a new classification scheme.
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published
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Journal / series
Volume
25 (1)
Pages / Article No.
163 - 179
Publisher
Springer
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Software
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Date collected
Date created
Subject
Macroseismic intensity; Amplification function; Site proxies; Soil classification
Organisational unit
02818 - Schweiz. Erdbebendienst (SED) / Swiss Seismological Service (SED)