Shallow Slow Slip Events Identified Offshore the Osa Peninsula in Southern Costa Rica from GNSS Time Series

Using new continuous GNSS time series from the region, we identify 5 distinct shallow SSEs that occurred immediately offshore and beneath the Osa peninsula: an event detected by one site in 2013, and two events occurring in close succession in both 2018 and 2022 detected by multiple stations, indicating a preliminary recurrence interval of ~4-5 years. While SSEs have been observed to the north at Nicoya, this is their first documentation in southern Costa Rica. Modeled slip distributions of the 2018 and 2022 events indicate that they ruptured the same or overlapping patches of the plate interface, nearly at the trench, updip of historic earthquakes including the 1983 Mw 7.4 Osa event. Immediately offshore, the estimated cumulative slip from the 2018 and 2022 events is sufficient to close the slip deficit from tectonic loading over the recurrence interval, likely influencing the magnitude and spatial slip distribution of future large ruptures.