Abstract
Many applications related to ground-motion studies and engineering seismology benefit from the opportunity to easily download large dataset of earthquake recordings with different magnitudes. In such applications, it is important to have a reliable seismic characterization of the stations to introduce appropriate correction factors for including site amplification. Generally, seismic networks in Europe describe the site properties of a station through geophysical or geological reports, but often ad-hoc field surveys are missing and the characterization is done using indirect proxy. It is then necessary to evaluate the quality of a seismic characterization, accounting for the available site information, the measurements procedure and the reliability of the applied methods to obtain the site parameters.In this paper, we propose a strategy to evaluate the quality of site characterization, to be included in the station metadata. The idea is that a station with a good site characterization should have a larger ranking with respect to one with poor or incomplete information. The proposed quality metric includes the computation of three indices, which take into account the reliability of the available site indicators, their number and importance, together with their consistency defined through scatter plots for each single pair of indicators. For this purpose, we consider the seven indicators identified as most relevant in a companion paper (Cultrera et al. 2021): fundamental resonance frequency, shear-wave velocity profile, time-averaged shear-wave velocity over the first 30 m, depth of both seismological and engineering bedrock, surface geology and soil class.
Highlights
In recent years, the number of stations of permanent seismic networks worldwide has largely increased
We evaluated the overall quality of a seismic characterization at a given site accounting for the seven indicators selected in Cultrera et al (2021): the fundamental resonance frequency (f0), the shear-wave velocity profile (VS) as function of depth, the time-averaged shear-wave velocity over the first 30 m (VS30), the seismological bedrock depth (Hseis_bed, which is defined as the depth of the geological unit controlling the fundamental resonance frequency), the engineering bedrock depth (Heng_bed, the depth at which VS reaches first in the profile the value of a specific value; for example H800 refers to VS = 800 m/s), the surface geology and the soil class
In order to reduce such bias for each of the seven site indicators, we believe an expert judgment is necessary in the Quality index 1 (QI1) assessment; the quality evaluation should be in the responsibility of the analysis team and/ or of the network operators involved in site characterization
Summary
The number of stations of permanent seismic networks worldwide has largely increased. It is necessary to define standards and quality indicators, for site characterization information at seismic stations to reach high-level metadata These topics are becoming a key issue within the European Union and worldwide. Some benchmarks were performed to test the reliability among different methods, especially to validate the performance of non-invasive and invasive methods for the measurements of shear-wave velocity profiles (Asten and Boore 2005; Stephenson et al 2005; Cornou et al 2009; Moss et al 2008; Cox et al 2014; Garofalo et al 2016; Darko et al 2020) These benchmarks have outlined the feasibility of non-invasive and invasive methods in supplying comparable results together with an estimate on inter-analysts variability. The results allow to rank the seismic stations according to their site characterization
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