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Session: Modeling and Understanding of High-Frequency Ground Motion [Poster]

Type: Poster

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

[Withdrawn] Influence of Coupling and Installation Depth of Accelerometric Station on Signal High-Frequency Content

Numerous accelerometric stations are assumed to be installed in free field conditions and hence, considered to be able to record the true ground motion without any alteration. However, recent experiments showed large differences in high frequency content between stations located very close to each other (less than 2 m) depending on whether the station is buried and firmly coupled to soil (classical ‘post seismic’ survey setup) or whether the station in anchored on a small concrete slab inside a shallow manhole (classical permanent network setup).

With respect to soil site conditions and based on the analysis of earthquake records, we observed large amplification above 10 Hz and up to a factor of 3 at 20 Hz for a station installed on concrete slab with respect to a collocated buried one. The differences between buried and slab-anchored stations seem to be much smaller in case of rock site conditions.

Stations may also be installed at shallow depths (few meters) within a seismic vault or cave and still considered as “free field”. In such configuration, the down-going waves interference with the up-going ones may induce important deamplification of the signal within a frequency band, which, although in the high frequency part of the earthquake spectrum, is still of importance for earthquake engineering.

The effect of the sensor installation practices on recorded high-frequency ground motion need to be better characterized and pertinent information should be disseminated as part of the station’s metadata in order to be taken into account for a better use of records. Indeed, the high frequency content of ground motion records has become an increasingly important topic within the framework of site-specific seismic hazard studies. A lot of studies, involving the “kappa” parameter concept, scattering analysis, etc., are using the high frequency part of the accelerometric signals provided by seismological networks.

Presenting Author: Fabrice Hollender

Additional Authors