Seismic Swarm Near the Coast of Nicaragua: April 2022 Analysis

A seismic swarm designated S20220421.1 occurred near the coast of Nicaragua between 07:42 on 21 April 2022 and 13:32 on 23 April 2022. Over 53 hours and 50 minutes, 33 earthquakes were recorded. The sequence began with a magnitude 6.6 event at a depth of 27 km, followed by numerous smaller events ranging from magnitude 2.5 to 4.0 at depths between 14 km and 46 km.

The events clustered tightly in time and space, characteristic of swarm activity rather than a classic mainshock-aftershock sequence. Notable events included a magnitude 4.0 quake at 46 km depth on 21 April at 09:06 and several magnitude 3.5–3.9 shocks distributed throughout the first two days. Activity tapered by the afternoon of 23 April, ending with a magnitude 3.0 event at 18 km depth.

Nicaragua lies within the tectonically active Central American subduction zone, where the Cocos Plate converges with and subducts beneath the Caribbean Plate at rates of approximately 8–9 cm per year. This setting produces frequent seismicity along the Middle America Trench offshore and within the volcanic arc onshore. The April 2022 swarm was located in the offshore portion of this margin, consistent with interplate or intraslab faulting.

Historically, the Nicaraguan segment of the subduction zone has generated destructive earthquakes, including the 1992 tsunami-generating event of magnitude 7.7 and the 2001 sequence near the Gulf of Fonseca. The region also hosts active volcanoes such as Momotombo and Concepción, underscoring the coupled volcanic-seismic hazard. Updated seismic monitoring by regional networks has improved detection of swarms, revealing episodic clusters often linked to fluid migration or slow slip along the plate interface.

The 2022 swarm provides insight into short-term strain release patterns offshore Nicaragua. The initial magnitude 6.6 shock likely triggered subsequent events through static stress changes, while the relatively shallow depths (mostly 20–30 km) suggest activity within the seismogenic zone of the subduction interface. No significant damage or tsunami was reported from this sequence, though it highlights the persistent seismic risk along the Pacific margin.

Further analysis of swarm statistics shows a rapid decay in event rate after the first 24 hours, with magnitudes generally decreasing. Such patterns aid in distinguishing swarms from foreshock sequences and support probabilistic forecasting efforts in subduction environments.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
SeismoSight internal swarm classification S20220421.1