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The initial instances of gradual sliding observed near the southern coast of Costa Rica.

A scientific monitoring instrument with a dome-shaped cover mounted on a tripod sits in a grassy strip of land between two forested areas.

The publication Geophysical Research Letters reports on scientific findings in the fields of Earth and Space Sciences.
The journal Geophysical Research Letters publishes research findings in the areas of Earth and Space Sciences.

Slow-slip events (SSEs) are slow earthquake ruptures that generate just a few centimeters of slip over periods ranging from days to years. They are thought to occur in many of the world’s subduction zones, but these subtle slips can be tricky to observe, especially when they happen under the ocean, where monitoring capabilities are often more limited than on land. Gaining a better understanding of where and how often SSEs occur is important, in part because they may modulate larger earthquakes that are more likely to cause damage and produce tsunamis.

Perry and colleagues offer fresh perspective on slow slip events (SSEs) by documenting five occurrences off the Osa Peninsula in southern Costa Rica, where the Caribbean Plate is subducting beneath the Cocos Plate. These SSEs, the first to be recorded in this region of Costa Rica, were observed in 2013, 2018, and 2022 through the use of data collected by a network of continuously operating Global Navigation Satellite System (GNSS) stations.

The registered SSEs are particularly noteworthy due to their occurrence at relatively shallow depths along the subduction zone. In contrast to deeper SSEs that occur on land, shallow events tend to rupture under the ocean and could potentially impact tsunami risks. The researchers determined that the amount of movement in the four most recent events (two in 2018 and two in 2022) appears to explain all of the tectonic convergence that built up in a specific area of the subduction zone over the past 4 years, possibly constraining the potential magnitude of future earthquakes.

According to a recent study published in Geophysical Research Letters, it is likely that there will be more large earthquakes near the Osa Peninsula, as there were three magnitude 7-7.5 events in the 20th century. The authors of the study believe that the new information gathered from shallow SSEs (slow slip events) off the coast of Costa Rica can aid in predicting where future earthquakes may occur in the region. The data also contributes to a better understanding of how slow slip impacts strain buildup and the potential timing and locations of SSEs.

—Rachel Fritts (@rachel_fritts), Science Writer

Reference: Fritts, R. (2023). Observing the initial slow-slip events in southern Costa Rica. Eos, 104. Published on October 23, 2023.

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