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Detection of Repeating Microearthquakes in Southeastern Costa Rica

Description: 

Despite its small area, Costa Rica’s tectonics are complex and diverse. Zooming into the southeastern region, the subduction of the rough and buoyant Cocos Ridge beneath the Panama microplate has produced a sequence of magnitude 7 and larger megathrust earthquakes roughly every 40 years. The last one, the 1983 M7.4 event beneath the Osa Peninsula, occurred 42 years ago. The likelihood of a similar event occurring in the near future is high, underscoring significant seismic hazard in southern Costa Rica. Recently, slow slip events have been identified off the coast of Osa Peninsula on the shallow plate interface up dip of the 1983 rupture. In some areas, these slow slip events release most of the accumulated slip over their four-to-five-year recurrence time. However, we still lack a detailed view of how fault slip on this interface is partitioned between aseismic creep, slow slip, and stick slip behaviors. Repeating earthquakes, which rupture the same small asperities at different times, provide a sensitive seismic marker of slow and/or aseismic slip on the plate interface, but they have not yet been systematically identified and analyzed in this segment. In this study, we use OVSICORI’s broadband stations around Osa Peninsula to detect and characterize families of repeating earthquakes along the plate interface. We apply strict criteria including robust waveform cross correlation and coherence, double difference relocation, S–P differential times, and source radius overlap to ensure that events in each family repeatedly rupture the same patch. Our preliminary results show several families of repeating events at different depths along the plate interface with different recurrence intervals. By tracking the cumulative seismic moment and inferred slip of these families through time, we aim to map the spatiotemporal distribution of fault slip in the region, estimate local slip and deficits, and place constraints on interplate coupling. These results will provide improved constraints for seismic hazard assessment, including the potential size and likely rupture area of the next large earthquake in southern Costa Rica.

Session: SSJ-SSOC-SSA Joint Session: From Slow to Fast Earthquakes: Bridging the Spectrum of Fault Slip [Poster]

Type: Poster

Date: 4/16/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Sonia Hajaji

Student Presenter: Yes

Invited Presentation: 

Poster Number: 146

Authors