Seismic Swarm S20220202.1 Near Guánica, Puerto Rico: Geological Context and Event Analysis

Puerto Rico occupies a tectonically complex zone at the boundary between the Caribbean and North American plates. The island experiences frequent seismicity driven by oblique convergence, with the Puerto Rico Trench marking the northern subduction margin and the Muertos Trough influencing southern deformation. Southwestern Puerto Rico, including the area around Guánica, lies near active fault systems such as the Guayanilla and Lajas faults, where shallow crustal stresses produce episodic earthquake swarms.

Swarm S20220202.1 began at 04:11 on 1 February 2022 and concluded at 00:13 on 11 March 2022. Centered 3 km west-southwest of Guánica, the sequence lasted 908 hours and one minute, registering 630 earthquakes. This activity fits within a documented pattern of recurrent swarms in the region since 2000, with eleven such episodes recorded through early 2022. Prior swarms occurred in 2018 (one), 2019 (one), 2020 (five), and 2021 (four).

Analysis of the first 100 events reveals a typical swarm signature of low-to-moderate magnitudes clustered in time and space. Magnitudes ranged from 1.1 to 2.9, with the majority falling between 1.5 and 2.5. Depths concentrated between 6 km and 17 km, indicating shallow crustal sources consistent with the local fault architecture. The sequence initiated with events near 2.0–2.3 magnitude at depths of 13–17 km, followed by a rapid increase in rate during the first 48 hours. Peak activity included multiple events above magnitude 2.5 on 2–4 February, such as a 2.9 event at 10 km depth on 2 February. Depths showed modest variation, occasionally reaching 19–20 km, while later events in the initial hundred maintained similar magnitude distributions without a dominant mainshock.

Such swarms reflect fluid migration or aseismic slip along pre-existing faults rather than a single large rupture. The 2022 sequence occurred in the same southern Puerto Rico seismic corridor that hosted the prolonged 2019–2020 activity, underscoring persistent strain accumulation in the area. No events in the examined subset exceeded magnitude 3.0, aligning with the swarm’s overall character of numerous small releases.

Continued monitoring by regional seismic networks remains essential for tracking evolving stress conditions in this tectonically active margin.

References
USGS Earthquake Catalog (earthquake.usgs.gov)
Puerto Rico Seismic Network – University of Puerto Rico at Mayagüez
SeismoSight internal swarm classification database