Poster of the Hojancha, Costa Rica Earthquake of 5 September 2012 - Magnitude 7.6

Tectonic Summary

The September 5th 2012 M 7.6 earthquake beneath the Nicoya Peninsula, Costa Rica, occurred as the result of thrust faulting on or near the subduction zone interface between the Cocos and Caribbean plates. At the latitude of this earthquake, the Cocos plate moves north-northeast with respect to the Caribbean plate at a velocity of approximately 77 mm/yr, and subducts beneath Central America at the Middle America Trench.

Over the past 40 years, the region within 250 km of the September 5th earthquake has experienced approximately 30 earthquakes with M 6 or greater; two of these were larger than M 7, and neither caused documented fatalities. The first was a M 7.2 in August of 1978, 9 km to the north-northeast of the September 5th event; the second had a magnitude of M 7.3, and struck a region just over 50 km to the east-southeast in March 1990. The earthquake of October 5, 1950, M 7.8, occurred in the general area of the September 5th 2012 earthquake, although the hypocenter of the earlier earthquake is not known to high precision. The 1950 earthquake caused damage in northwestern Costa Rica and in the Valle Central of Costa Rica, but no reported casualties. The closest earthquake to cause fatalities in recent history was the M 6.5 April 1973 earthquake, which occurred at shallow depth approximately 80 km to the northeast; the 1973 shock resulted in 26 fatalities and over 100 injuries.

Earthquake Report

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