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Determining First Motion Focal Mechanisms for Small Magnitude Earthquakes in the Southwestern Puerto Rico Seismic Sequence From January 6th and 7th, 2020

Description: 

The 2020 Southwestern Puerto Rico Seismic Sequence is a complex multiple fault sequence occurring a across a fault zone of relatively small strike-slip and normal faults. Prior to the M6.4 normal fault event the activity centered upon a strike-slip fault off-shore of the Punta Montalva Fault. Here the aim is to examine small magnitude events to pinpoint the initial focal mechanisms (FM) of movement that occurred between January 6 and 7, 2020, before and after the M6.4. Here a total of 35 earthquakes with M3-4 occurring on January 6-7 2020 in southwestern Puerto Rico were studied. The Bayesian Inversion method MTFit was applied to first motion data from the Puerto Rico Seismic Network (PRSN). Before analysis the PRSN data was manually examined and verified. Additionally, the P, SV, and SH amplitudes were manually picked to find determine the S/P amplitude ratios. The amplitude ratios were not included in the initial FM analysis as to avoid the influence of possible site or path effects, but will be included in future analyses. Of the 35 earthquakes analyzed, 26 produced distinguishable FMs. Of these, events prior to the M6.4 event predominantly consisted of strike-slip FMs suggesting that the conversion to a multiple fault sequence is likely due to stress transfer from the off-shore strike-slip fault to the normal fault associated with the M6.4.

Session: The 2020-2021 Southwest Puerto Rico Seismic Sequence: Current State of Knowledge and Implications [Poster]

Type: Poster

Date: 4/18/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Janluis Rivera Ramos

Student Presenter: Yes

Invited Presentation: 

Authors