Seismic Swarm VS20180112.1 in Costa Rica: Analysis and Geological Context

A seismic swarm designated VS20180112.1 occurred in Costa Rica, commencing at 14:40 on 11 January 2018 and concluding at 15:07 on 12 January 2018. During this 24-hour and 27-minute period, 26 earthquakes were recorded. The events exhibited magnitudes between 3.0 and 5.0, with focal depths ranging from 3 to 10 km, consistent with shallow crustal activity typical of the region's tectonic setting.

The sequence began with a magnitude 3.3 event at 5 km depth, followed shortly by two magnitude 4.6 shocks at depths of 7 km and 6 km. Subsequent activity included a magnitude 5.0 earthquake at 10 km depth, which represented the largest event in the swarm. Later phases featured additional events such as a magnitude 4.8 at 10 km and a magnitude 4.4 at 3 km, with many smaller tremors clustered at depths of 3 to 6 km. This pattern reflects a rapid succession of ruptures along local fault structures, releasing accumulated tectonic stress without a single dominant mainshock.

Costa Rica occupies a tectonically dynamic position at the convergent margin where the Cocos Plate subducts beneath the Caribbean Plate. This subduction drives the Central American Volcanic Arc and generates frequent seismicity through megathrust earthquakes, intraslab events, and upper-plate faulting. The January 2018 swarm aligns with shallow activity often linked to the volcanic front or secondary faults accommodating oblique convergence. Historical records indicate that such swarms are episodic, with the preceding instance in 2011 marking the only prior occurrence since 2000.

These swarms provide insights into transient stress changes and fluid migration within the crust, potentially influenced by nearby volcanic systems such as those in the Cordillera Central. Monitoring data from this event contribute to refined models of regional hazard assessment, emphasizing the importance of continuous seismic networks for early detection of unrest.

References

• United States Geological Survey Earthquake Catalog
• Costa Rica National Seismological Network (RSN) reports
• Global CMT Project focal mechanism database