Seismic Precursors in Central Italy using Coherence of Correlated Waveforms
Abstract
High magnitude earthquakes in Italy occur mainly in the Apennines: L'Aquila (2009 - M6.3) and the Amatrice, Visso, Norcia sequence in 2016 (M6.2; M6.1 and M6.5 respectively). These earthquakes are sometimes preceded by foreshocks (L'Aquila), or not (Amatrice) which makes it difficult, or even impossible, to predict them. In our study, we introduce a new measurement based on the coherence of correlated waveforms (CCW) associated with ambient seismic noise. The technique is sensitive to attenuation changes in the medium, unlike dv/v method. We show that the L'Aquila earthquake is preceded by a 150-day oscillatory signal whose amplitude and frequency gradually increases until the failure. A similar oscillation is measured during the 200 days preceding the Amatrice earthquake (2016). The similarity of the schemas underlines the existence of a single nucleation process, of a minimum duration of several months. The nucleation process is associated with a geographical extension that shows a progressive localization towards the epicentral zone. These two characteristics open the possibility of predicting the location of the main rupture within a time window of a few months. The Visso and Norcia earthquakes may also be associated with a precursory signal, but the importance of Amatrice's post-seismic recovery makes it difficult to interpret our measurements. In order to improve the rapid recognition of the precursory signal and to avoid any expert judgment, we use the tools of supervised Machine Learning (Random Forest and Support Vector Machine). Preliminary results indicate a recognition of the {rest}, {precursor} and {post-seismic} classes with a success rate of 98% ± 1.5% when working on one-day windows, which allows very early recognition of the precursor signal.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S24A..08D
- Keywords:
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- 1242 Seismic cycle related deformations;
- GEODESY AND GRAVITY;
- 7215 Earthquake source observations;
- SEISMOLOGY;
- 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGY;
- 8109 Continental tectonics: extensional;
- TECTONOPHYSICS