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Automated Detection and Characterization of Swarms and Mainshock-Aftershock Sequences in Southern Mexico

Description: 

Earthquakes in Mexico are frequent and dangerous. Over the last decade, there have been a dozen major earthquakes including two larger than M7.5. The Mexican subduction zone is considered a natural laboratory for studying slip processes due to the relatively short trench-to-coast distance which brings broad portions of the seismogenic megathrust inland. Using an automated detection algorithm that identifies clusters of events using the nearest neighbor distances in the space-time-energy domain (Zaliapin and Ben-Zion, 2013), we sought to characterize ~700 sequences detected from 2012 to 2020. Traditional methods are time-consuming and biased due to the number of events and human perception, so we developed an automated strategy to evaluate sequences on a spectrum of swarm to mainshock-aftershock (MS-AS). The automated algorithm uses quantitative forms of these attributes: 1) magnitude difference between the largest event and next largest events, 2) percentage of the sequence after the largest event, 3) slope of seismicity rate over time, 4) ratio of magnitude range to the number of events and, 5) rate of maximum magnitude decay over time. The automated method yields similar results to manual characterization and is effective at identifying average properties when there are discrepancies among manual ratings for complex sequences. We found more swarms than aftershock sequences despite the prominence of large megathrust MS-AS sequences over the past decade. Temporally, some swarm sequences show an interesting pattern where the seismicity shuts on or off depending on nearby megathrust activity. Spatially, swarms help define a vertically dipping fault in the upper plate indicating a strike-slip sliver fault may be closer to the coast than previously thought. We anticipate standardizing the characterization process will provide opportunities for more in-depth studies of seismic sequence types and their causes.

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

Type: Oral

Date: 5/3/2024

Presentation Time: 03:00 PM (local time)

Presenting Author: Wilnelly

Student Presenter: Yes

Invited Presentation: Yes

Authors