M 6.9 - 2 km SSW of San Pablo, Guatemala

Tectonic Summary

The June 14, 2017 M 6.9 earthquake northeast of San Pablo, Guatemala, occurred as the result of normal faulting at an intermediate depth, approximately 100 km beneath the surface of coastal Guatemala. The focal mechanism solution indicates the earthquake occurred on either a shallowly dipping normal fault striking southeast, or on a steeply dipping normal fault striking northwest. At the location of the earthquake, the Cocos plate converges with the North America plate at a rate of approximately 79 mm/yr, subducting beneath North America lithosphere at the Middle America Trench, 200 km to the southwest of this earthquake. The mechanism, location, and depth of the June 14th event indicate that the earthquake occurred within the subducting Cocos plate, rather than on the shallow thrust interface between the two plates.

Central America is very seismically active, and the region within 250 km of the June 14, 2017 event has experienced 34 other M 6.5+ earthquakes over the preceding century. Most occurred on or near the shallow plate interface in this region. Only two such earthquakes have occurred at intermediate depths, both to the northwest of the June 14, 2017 earthquake beneath southern Mexico – a M 6.9 earthquake at a depth of 165 km in March 1994, and a M 6.6 event at a depth of 85 km in December 2015. The latter event caused two fatalities, and landslides near the coast.

The June 14, 2017 event also follows a series of shallow earthquakes on or near the subduction thrust interface about 150 km to the southwest. Since late May 2017, 16 earthquakes of M 4.1 and larger have occurred there, including a M 5.5 event on June 10th with a thrust faulting mechanism, and M 5.4 and M 5.5 thrust faulting earthquakes on June 14th in the hour prior to the M 6.9 event.

Earthquakes like this event, with focal depths between 70 and 300 km, are commonly termed "intermediate-depth" earthquakes. Intermediate-depth earthquakes represent deformation within subducted lithosphere rather than at the shallow plate interfaces between subducting and overriding tectonic plates. They typically cause less damage on the ground surface above their foci than is the case with similar-magnitude shallow-focus earthquakes, but large intermediate-depth earthquakes may be felt at great distance from their epicenters. Earthquakes have been reliably located to depths of just over 200 km in this region.