Enhanced Detection and Swarm Behavior of the Indios, Puerto Rico Earthquake Sequence

Session: Early Results from the 2020 M6.4 Indios, Puerto Rico Earthquake Sequence [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The recent Puerto Rico earthquake sequence has drawn attention as the seismicity rate in this area is unprecedented. Initial locations and focal mechanisms have indicated a network of strike-slip and normal faults. This sequence has swarm characteristics (high seismicity rate without a clear triggering mainshock, an abrupt beginning, lack of Bath’s Law), which presents challenges for operational earthquake forecasting. Due to the high seismicity rate that has limited time to characterize the earthquakes, the publicly available catalog has lacked smaller magnitude (<2) earthquakes since Jan 2. We employed template matching to improve the detection of smaller seismicity and better understand the spatiotemporal patterns of this sequence. Our preliminary analysis has focused on maximizing real detections and reducing detection of noise, along with magnitude estimation. Our initial scans have identified ~20,000 matches using the three stations with the best signal to noise ratio and ~1,750 cataloged events from Dec 28 to Jan 16 as templates. The enhanced catalog illuminates the swarm patterns, with a remarkable lack of Omori decay, particularly at smaller magnitudes. After the initial burst of events on Dec 28, the seismicity maintains an average rate of ~20/hour until Jan 3, when it starts to decrease. Following the burst on Jan 6, an average rate of ~50/hour is sustained for ~10 days. The swarm characteristics argue against an internally driven static stress triggering (e.g., swarm events triggering each other) and for an external triggering mechanism (e.g., slow slip, fluid movement). We found evidence of the swarm pattern throughout where the sequence has migrated, indicating that the driving mechanism is present across multiple fault strands and types. This suggests either slow slip propagated between several fault structures and orientations during this sequence or a fluid source established high pore fluid pressure conditions across a 40km-wide fault network.

Presenting Author: Wilnelly A. Ventura-Valentin

Authors