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Informative modes in the nearest-neighbor earthquake diagram

Yu-Fang Hsu, Ilya Zaliapin, & Yehuda Ben-Zion

Submitted September 11, 2022, SCEC Contribution #12091, 2022 SCEC Annual Meeting Poster #016

The nearest-neighbor analysis of seismicity (e.g., Zaliapin and Ben-Zion, J. Geophys. Res., 2013) has multiple applications including earthquake cluster detection and classification, catalog declustering, and induced seismicity characterization. It distinguishes two prominent modes (background and clustered) based on the 2-dimensional joint distribution (T, R), which is calculated by a proximity measure η, a product of rescaled time T and rescaled distance R between earthquakes. This work aims to identify additional informative modes in the nearest-neighbor diagram. We analyze different earthquake catalogs in California and observe several distinguishing modes of seismicity involving induced seismicity, repeating earthquakes, and large vs. small aftershock sequences in nearest-neighbor diagrams. Most of the induced earthquakes in the Geyser and Coso geothermal fields are in the diagram’s background domain. This induced seismicity mode has similar overall η values as tectonic background seismicity but with larger rescaled time T and smaller rescaled distances R. The mode of repeating earthquakes is mainly observed in parts of the creeping section of the San Andreas fault, and is characterized by very large rescaled time T and small rescaled distances R, compared to the cluster mode of tectonic earthquakes. Moreover, aftershock sequences of large and small-to-medium magnitude mainshocks occupy different parts of the cluster mode. We also document significant differences in the triggering properties of different catalogs that likely reflect differences in the catalog construction. These distinguishing features in the (T, R) diagram reveal important aspects of seismicity in addition to the general background and clustered modes.

Key Words
nearest-neighbor analysis of seismicity, earthquake clustering, aftershock sequences, declustering, induced seismicity, repeating earthquakes

Hsu, Y., Zaliapin, I., & Ben-Zion, Y. (2022, 09). Informative modes in the nearest-neighbor earthquake diagram. Poster Presentation at 2022 SCEC Annual Meeting.

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