Community Geophysical Event Response to the 5 September 2012, Mw=7.6 Nicoya Peninsula, Costa Rica Earthquake

Overview

On Wednesday, September 5, 2012, at 14:42:07 UTC, a magnitude 7.6 earthquake struck roughly 40 km (25 miles) below the surface of the Earth, 10 km (6.2 miles) ESE of the city of Nicoya, Costa Rica. This earthquake occurred beneath the Nicoya Peninsula of Costa Rica as the result of thrust faulting on the subduction zone interface between the subducting Cocos and overriding Caribbean plates. At this latitude, the Cocos plate moves north-northeast with respect to the Caribbean plate at approximately 77 mm/yr, and subducts beneath Central America at the Middle America Trench, as determined by GPS observations supported by UNAVCO. Preliminary estimates show that approximately 3 meters of slip occurred on the interface between the two plates.

The Nicoya peninsula last experienced an earthquake of similar magnitude (M7.7) in 1950, and an event of similar size has been expected for the past several years (e.g. Feng et al, 2012). In collaboration with OVISCORI, the Costa RIcan National Volcanic and Seismic Observatory the UNAVCO community has invested many resources to build multiple continuously operating GPS stations that adequately instrument the Nicoya Pennisula where the earthquake occurred. The network was upgraded by UNAVCO and OVSICORI staff in January 2012, and three weeks before the M7.6 earthquake was featured in the article "Sensors in place to measure next big Nicoya quake".

GPS observations have also shown that the Nicoya peninsula is subject to Episodic Tremor and Slip (ETS) events (Outerbridge et al, 2010). The May, 2007 ETS event involved approximately 2 cm. of slip on the plate-bounding fault that appears to have slipped on September 5th.

View more details about this earthquake at USGS Event Page.

For detailed information we recommend this excellent presentation: MARGINS 2009 Presentation on Nicoya GPS, Earthquakes, and ETS by Prof. Tim Dixon of the University of South Florida.

Over the past two decades, the UNAVCO community has invested many resources to build multiple continuously operating GPS stations that adequately instrument the Nicoya Pennisula where the earthquake occurred.