Seismotectonic Analysis of the 2019–2020 Puerto Rico Sequence: The Value of Absolute Earthquake Relocations in Improved Interpretations of Active Tectonics

We present a new catalog of calibrated earthquake relocations from the 2019–2020 Puerto Rico earthquake sequence related to the 7 January 2020 Mw 6.4 earthquake that occurred offshore of southwest Puerto Rico at a depth of 15.9 km. Utilizing these relocated earthquakes and associated moment tensor solutions, we can delineate several distinct fault systems that were activated during the sequence and show that the Mw 6.4 mainshock may have resulted from positive changes in Coulomb stress from earlier events. Seismicity and mechanisms define (1) a west–southwest (∼ 260°) zone of seismicity comprised of largely sinistral strike-slip and oblique-slip earthquakes that mostly occurs later in the sequence and to the west of the mainshock, (2) an area of extensional faulting that includes the mainshock and occurs largely within the mainshock’s rupture area, and (3) an north–northeast (∼ 30°)-striking zone of seismicity, consisting primarily of dextral strike-slip events that occurs before and following the mainshock and generally above (shallower than) the normal-faulting events. These linear features intersect within the Mw 6.4 mainshock’s fault plane in southwest Puerto Rico. In addition, we show that earthquake relocations for M 4+ normal-faulting events, when traced along their fault planes, daylight along east–west-trending bathymetric features offshore of southwest Puerto Rico. Correlation of these normal-faulting events with bathymetric features suggests an active fault system that may be a contributor to previously uncharacterized seismic hazards in southwest Puerto Rico.

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Work Title Seismotectonic Analysis of the 2019–2020 Puerto Rico Sequence: The Value of Absolute Earthquake Relocations in Improved Interpretations of Active Tectonics
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Open Access
Creators
  1. Copeland W. Cromwell
  2. Kevin P. Furlong
  3. Eric A. Bergman
  4. Harley M. Benz
  5. Will L. Yeck
  6. Matthew Herman
License In Copyright (Rights Reserved)
Work Type Article
Publisher
  1. Seismological Research Letters
Publication Date December 8, 2021
Publisher Identifier (DOI)
  1. https://doi.org/10.1785/0220210238
Deposited February 12, 2024

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Version 1
published

  • Created
  • Added srl-2021238.1.pdf
  • Added Creator Copeland W. Cromwell
  • Added Creator Kevin P. Furlong
  • Added Creator Eric A. Bergman
  • Added Creator Harley M. Benz
  • Added Creator Will L. Yeck
  • Added Creator Matthew Herman
  • Published
  • Updated Publisher, Publication Date Show Changes
    Publisher
    • Earthquake Notes - Seismological Society of America, Eastern Section,
    • Seismological Research Letters
    Publication Date
    • 2022-03-01
    • 2021-12-08
  • Updated