A Detailed View of the 2020-2023 Southwestern Puerto Rico Seismic Sequence with Deep Learning
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1.
United States Geological Survey
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2.
University of Puerto Rico-Mayaguez
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3.
California Institute of Technology
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4.
British Antarctic Survey
Abstract
The 2020–2023 southwestern Puerto Rico seismic sequence, still ongoing in 2023, is remarkable for its multiple-fault rupture complexity and elevated aftershock productivity. We applied an automatic workflow to continuous data from 43 seismic stations in Puerto Rico to build an enhanced earthquake catalog with ∼180,000 events for the 3+ yr sequence from 28 December 2019 to 1 January 2023. This workflow contained the EQTransformer (EQT) deep learning model for event detection and phase picking, the EikoNet-Hypocenter Inversion with Stein Variational Inference probabilistic earthquake location approach with a neural network trained to solve the eikonal wave equation, and relocation with event-pair waveform cross correlation. EQT increased the number of catalog events in the sequence by about seven times, though its performance was not quite as good as thorough analyst review. The enhanced catalog revealed new structural details of the sequence space–time evolution, including sudden changes in activity, on a complex system of many small normal and strike-slip faults. This sequence started on 28 December 2019 with an M 4.7 strike-slip earthquake followed by 10 days of shallow strike-slip foreshocks, including several M 5+ earthquakes, in a compact region. The oblique normal fault Mw 6.4 mainshock then happened on 7 January 2020. Early aftershocks in January 2020, with several M 5+ earthquakes, quickly expanded into two intersecting fault zones with diffuse seismicity: one extending ∼35 km on a northward-dipping normal fault and the other ∼60-km-long and oriented west-northwest–east-southeast on strike-slip faults. Months to years later, aftershocks moved westward, deeper, and to outer reaches of the active fault zones, with abrupt rapid seismicity migration following larger M 4.7+ aftershocks in May, July, and December 2020. The observed seismicity evolution indicates cascading failure from stress transfer on multiple critically stressed faults. High aftershock productivity results from the complex multiple-fault network hosting the sequence, which is characteristic of an immature fault system in the diffuse deformation zone around Puerto Rico, at the complicated North American–Caribbean plate boundary region.
Copyright and License
© 2023 Seismological Society of America.
Acknowledgement
This research would not be possible without the contributions of technical and monitoring staff at the Puerto Rico Seismic Network (PRSN) and their partners, who deserve special gratitude, for the following: station installs and upgrades, data flow maintenance, monitoring, software operation and maintenance, and earthquake products. The PRSN analyst team maintains a top‐notch quality earthquake catalog. U.S. Geological Survey colleagues worked with PRSN staff to install the temporary stations GS.PR01–GS.PR06, which were essential in their ability to identify and locate earthquakes in this sequence. The authors also thank the developers and maintainers of open‐source software for seismology, geophysics, and machine learning, listed in the Data and Resources, which was foundational to this research. The authors thank Zachary Ross for help with calculating the Hypocenter Inversion with Stein Variational Inference locations and a large number of cross‐correlation differential times on graphics processing units. Nicholas van der Elst helped them calculate b‐value and Mc with the b+ estimator. Rapid Earthquake Association and Location event association and cross‐correlation differential time calculations were accelerated with the help of central processing units (CPUs) and GPUs on the National Aeronautics and Space Administration Ames High‐End Computing Capability supercomputers; the authors thank Sarah Minson, Steve Hickman, and Chris Henze for facilitating access to this essential computing resource. Rob Skoumal, Mostafa Mousavi, and an anonymous reviewer provided helpful reviews of the article. The authors had helpful discussions about the Puerto Rico earthquake sequence with Jeanne Hardebeck, Andy Michael, Morgan Page, Sandra Rosero Rueda, David Shelly, Jacob Walter, and Weiqiang Zhu. The EQTransformer performance evaluation was inspired by analysis done by Ryan Tam and discussions with Jen Andrews, Rayo Bhadha, Egill Hauksson, Ellen Yu in the Caltech Seismo Lab.
Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Data Availability
We downloaded Puerto Rico Advanced National Seismic System Comprehensive Catalog (ComCat) events (doi: 10.5066/F7MS3QZH) with the ComCat webservice (https://earthquake.usgs.gov/fdsnws/event/1, last accessed February 2023), which are contributed by the Puerto Rico Seismic Network (PRSN; doi: 10.7914/SN/PR, https://redsismica.uprm.edu, last accessed February 2023). Continuous seismic data were downloaded from the EarthScope Seismological Facility for the Advancement of Geoscience (formerly Incorporated Research Institutions for Seismology) data management center through web services (https://service.iris.edu, last accessed February 2023), with data contributed by the PRSN (doi: 10.7914/SN/PR), Global Seismographic Network; doi: 10.7914/SN/IU), and the U.S. Geological Survey temporary network (doi: 10.7914/SN/GS). The source code for open‐source seismology software was obtained from the following links. EQTransformer at https://github.com/smousavi05/EQTransformer (last accessed April 2023), Rapid Earthquake Association and Location at https://github.com/Dal-mzhang/REAL (last accessed April 2023), EikoNet at https://github.com/Ulvetanna/EikoNet (last accessed April 2023), Hypocenter Inversion with Stein Variational Inference at https://github.com/Ulvetanna/HypoSVI (last accessed April 2023), GrowClust at https://github.com/dttrugman/GrowClust (last accessed April 2023). Scripts used to process Puerto Rico seismic data and generate plots: https://gitlab.com/cyoon1/puerto-rico-scripts (last accessed April 2023). Scripts used to calculate cross correlation differential times for GrowClust relative location: https://gitlab.com/cyoon1/stasis_bin (last accessed April 2023) and https://gitlab.com/cyoon1/stasis_puerto_rico (last accessed April 2023). We used ObsPy 1.4.0 (Krischer et al., 2015; https://www.obspy.org, last accessed April 2023) for seismological data processing and visualization and Generic Mapping Tools (GMT) 6.4.0 (Wessel et al., 2019; https://www.generic-mapping-tools.org/, last accessed April 2023) to generate maps. BlocklyEQTransformer software package (Mai and Audet, 2022) is available at https://github.com/maihao14/BlocklyEQTransformer (last accessed April 2023). Faults plotted in Figure 1 are from these fault databases: Styron and Pagani (2020), Global Earthquake Model Global Faults Active Database at https://github.com/GEMScienceTools/gem-global-active-faults (last accessed April 2023); French and Schenk (2004), Faults of the Caribbean Region at https://www.sciencebase.gov/catalog/item/60a81702d34ea221ce4e5b49 (last accessed April 2023); Coffin et al. (1998), Present‐Day Plate Boundaries at http://www-udc.ig.utexas.edu/external/plates/data.htm (last accessed April 2023) (ridge.gmt, transform.gmt, trench.gmt). Elevation (bathymetry and topography) in Figure 1 are from GMT 6.0 Global Earth Relief Grids sampled at 15 s: https://docs.generic-mapping-tools.org/6.0/datasets/earth_relief.html (last accessed April 2023). The supplemental material contains circular rupture area estimation for depth cross sections; data sources for Mw 6.4 mainshock finite‐fault inversion; Tables S1–S9 with detailed station data and input parameters; Figures S1–S21 with additional analysis details; Movies S1–S4 and captions with 3D seismicity visualizations; and Data Sets S1–S5 with different earthquake catalogs in text format; and references in the supplement.
Supplemental Material
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Additional details
- Available
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2023-07-06Published online
- Caltech groups
- Division of Geological and Planetary Sciences, Seismological Laboratory
- Publication Status
- Published