Poster #251, Earthquake Forecasting and Predictability (EFP)

Earthquake clustering and localization of seismicity before large events

Ilya Zaliapin, & Yehuda Ben-Zion
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Poster Presentation

2021 SCEC Annual Meeting, Poster #251, SCEC Contribution #11504 VIEW PDF
We present recent results focused on assessing the degree of regional clustering of earthquakes and progressive localization of seismicity in relation to the earthquake cycle. First, we demonstrate that events included in the existing short-duration instrumental catalogs are concentrated within a very small fraction of the space-time volume, which is highly amplified by activity associated with the largest recorded events. The earthquakes that are included in instrumental catalogs are unlikely to be fully representative of the long-term behavior of regional seismicity, creating a bias in a range of seismicity analyses. The results justify earthquake declustering and suggest a new metric for ...assessing quality of declustering (independent of a particular declustering technique). The second part focuses on progressive localization of seismicity, which corresponds to mechanical evolution of deformation from distributed failures in a rock volume to localized shear zones, culminating in generation of primary slip zones and large earthquakes. We present a methodology for estimation of localization using earthquake catalogs and showcase its applications to tracking preparation processes of large earthquakes. This analysis is performed with declustered catalogs. Methodologically, both discussed topics are based on the Receiver Operating Characteristic (ROC) analysis of seismicity. We demonstrate how this unified framework is adopted for diverse tasks, including assessment of coupled space-time clustering after controlling for space and time marginal inhomogeneities of earthquake rates, and tracking time-dependent transformations of a highly inhomogeneous earthquake space distribution. The examined data include crustal seismicity in California, Alaska and other regions, synthetic catalogs of the ETAS model, and acoustic emission data of laboratory fracturing experiments.