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A Comparison of the Stress Drop Estimates Derived From Different Techniques in Pollino, Italy

Seismic spectral estimates of earthquake stress drop remain controversial, subject to large uncertainties, despite the fundamental role the source parameter plays in assessing the seismic forecasting in a given area and in improving ground motion predictions for seismic hazard mitigation. Comparing different measurement techniques to understand how analysis processes affect the resulting estimates of stress drops is a necessary first step to improve resolution. It can also be useful to perform the same procedures using different data sets. In this study we focus on the Pollino area, southern Apennines, where structural complexities are thought to control seismic activity. We compare estimates of the Brune-style stress drop for 100 earthquakes (M2.2-5.2) derived from two techniques: spectral fitting for attenuation, site effects and source), and spectral ratio fitting in which an empirical Green’s function event is assumed to remove the path and site effects. In all cases, the Brune (1970) source is assumed. In the spectral fitting we first assume a regional attenuation model, and second estimate path attenuation from the high-frequency decay of 8 well-recorded earthquakes (M3.6-5.2), to obtain attenuation-corrected spectra. We estimate and remove the site term in both cases by averaging the attenuation-corrected spectra for each event, and then computing the difference from the mean event spectrum for each station (assuming the mean site correction is zero). These differences are averaged over the event ensemble to obtain a mean site term for each station, which is then removed before fitting the resulting estimates of source spectra to obtain the final source parameter estimates. In the EGF approach, we divide the spectra of the target events by those of co-located smaller EGF earthquakes, and fit the resulting spectral ratios, for each event, at each station, assuming all path and site effects are removed. We perform the fitting first with no constraints on the stress drop (and corner frequency) of the EGF event, and then with constraints based on different scaling laws of stress drop to seismic moment.

Session: Understanding and Quantifying the Variability in Earthquake Source Parameter Measurements [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Giovanna Calderoni

Student Presenter: No

Additional Authors