Seismotectonics of Puerto Rico Trench Using Ocean Bottom Seismographs

Session: Ocean Bottom Seismology – New Data, New Sensors, New Methods [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Passive seismic experiments in the marine environment are highly cost-effective and unique in addressing major hazards related to active margins. This study incorporates the data collected by six ocean bottom seismometers (OBS) operated by USGS offshore of Puerto Rico (Mid-2015 to Mid-2016) with land-based Puerto Rico Seismic Network. The Puerto Rico trench is a complex transition of a progressively more oblique convergence from east to west. We focus on a 100 km² region of this transition north of the Virgin Islands, which is characterized by frequent earthquake swarms and by a change from a typical forearc morphology to a collapsed forearc. A better understanding of active tectonics in the region requires a spatial resolution and known mechanism for seismic sources. We use the Hypocentroidal Decomposition algorithm (MLOC) for relocation and the Computer Programs in Seismology for source inversion. A total of 278 events are relocated so far, 36 of which are from the ISC catalog with M > 4 and from 2006 to 2019. The OBS data (836 P-wave and 190 S-wave arrivals) used in the inversion substantially improved the azimuthal coverage for seismicity that predominantly occurs offshore. The shallow seismicity within the overriding plate with strike-slip motion is probably related to the deformation of the Bunce fault. Seismicity to the south is clustered at 64.8°W,19.1°N with depths between 20-33 km and a reverse mechanism that may represent deformation at top of the subducting plate interface. The seismicity northwest of this point shows similar depth distribution and oblique reverse faulting. Southeast of this point, normal faulting parallel to the NE-trending Anegada passage is observed at ~30 km depth. NW-trending shallow seismicity and NE-trending deeper seismicity with reverse faulting are observed south of 19.1°N. About 35 percent of seismicity may represent strain partitioning on different structures in the overriding plate. Another 36 percent of seismicity represents deformation along the coupled interface between plates ~20 km depth and the rest are deeper than 30 km.

Presenting Author: Asiye Aziz Zanjani

Authors