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Earthquake Swarms as a Window to Characterize Transient Processes

Description: 

Earthquake swarms are broadly defined as earthquake sequences without a distinct mainshock. Many different parameters have been proposed to characterize earthquake swarms and distinguish them from mainshock-aftershock sequences. However, there is no universal definition of swarms. In this study, we compile previously identified earthquake swarms in different tectonic regions, including tectonic strike-slip faults, volcanic and geothermal regions, and fluid-induced swarms in the intraplate region. We obtain a comprehensive set of physical and statistical parameters to characterize the swarm evolution in space and time and compare swarms from different tectonic regions. For two swarms driven by different external processes, we further characterize short-duration bursts within the swarm.

Preliminary analysis found no systematic difference in effective stress drop from different regions with values ranging up to 3 orders of magnitude. The range of effective stress drop is similar to static stress drop for individual earthquakes, suggesting the average stress release is nearly constant. The skewness of moment release history is mostly small, however, several prolific swarms from the Salton Trough have very high skewness, suggesting more concentrated moment release during the early stage of the swarm - a behavior that is more similar to foreshock-mainshock-aftershock sequences.

A systematic difference in the scale exponent between migration velocity and swarm duration separates swarms into different groups of different dominant triggering processes from pressure-diffusion dominant to shear-stress-transfer dominant regimes. An effective diffusivity is obtained based on the product of velocity squared and duration. Relatively narrow ranges of diffusivity are found for each group, with the Salton Trough being systematically higher and bridging the gap between crustal swarms and slow-slip events. We hypothesize that such observation suggests characteristic diffusion processes in different tectonic regions, and swarm parameters reflect characteristic transient processes in different environments.

Session: Advances in Operational and Research Analysis of Earthquake Swarms -II

Type: Oral

Date: 5/3/2024

Presentation Time: 05:00 PM (local time)

Presenting Author: Xiaowei

Student Presenter: No

Invited Presentation: Yes

Authors