Looking at the Between-Event Variability From the Source Parameters Point of View: A Test Case in Central Italy

Date: 4/25/2019

Time: 09:15 AM

Room: Pine

Ground-motion prediction equations (GMPEs) compute both the median predictions and the aleatory variability for any seismic scenario of interest. The between-event component of the aleatory variability absorbs repeated source effects that are not captured by magnitude differences among the analyzed earthquakes. The rapid increase of strong-motion data availability fostered studies aiming at partitioning the (apparent) aleatory variability by identifying repeatable event, source, or path effects, allowing for a seismological interpretation of specific residual component. Efforts for defining strategies to identify repeatable residuals took advantage of the availability of rich data sets. We analyze a data set of earthquakes that occurred in central Italy since 2008. We first isolate the source, propagation and site contributions to the S-waves Fourier spectra by applying a spectral inversion technique. Then, we develop a set of GMPEs to interpret the between-event residual distributions in terms of source parameters. Because different magnitude scales measure the earthquake size from different points of view, we also evaluate the impact of using moment (Mw), local (ML) or energy (Me) magnitude. We show that the between-event residuals obtained using Mw are correlated with stress drop, with correlation coefficients increasing with increasing frequency up to about 10 Hz. Contrariwise, the correlation is weak using ML and Me, in particular between 2 and 5 Hz, where most of the corner frequencies lie. The correlation with the source parameters reflects in a different behavior of the standard deviation tau of the between-event residuals with frequency. Although below 1.5 Hz tau is smaller for the GMPE using Mw, at higher frequencies the model implementing either ML or Me shows smaller tau, with a reduction of about 30% at 3 Hz. Finally, we show that the temporal changes of the between-event residuals resemble those of the stress drop which, in turn, mirrors the relative seismic-velocity variations observed in previous studies for the same area.

Presenting Author: Dino Bindi

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