M 6.8 - 28 km SW of Puerto San José, Guatemala

Tectonic Summary

The June 22, 2017 M 6.8 earthquake offshore of Guatemala occurred as the result of shallow thrust faulting on or near the subduction zone interface in the region. At the location of this earthquake, the Cocos plate converges with the Caribbean plate at a rate of 69 mm/yr towards the northeast, and subducts beneath Central America at the Middle America Trench, 110 km to the southwest of this earthquake. The June 22nd event is located near to the triple junction between the Cocos, Caribbean, and North America tectonic plates; just to the northwest of this earthquake, the Cocos plate subducts beneath the North America plate at the slightly faster rate of 79 mm/yr, accommodating left-lateral strike-slip motion between the Caribbean and North America plates near the surface in south-central Guatemala. The location, depth, and focal mechanism solution of the June 22nd earthquake are all consistent with the event occurring on the subduction zone interface.

Central America is very seismically active, and the region within 250 km of the June 22, 2017 event has experienced 35 other M 6.5+ earthquakes over the preceding century. Most also occurred on the shallow plate interface in this region. The largest was a M 7.7 earthquake in August 1942, 25 km to the northwest of today’s earthquake, which caused 38 fatalities and triggered many landslides along the coast of Guatemala. A M 6.8 in October 1979, 15 km to the northeast of the June 22, 2017 earthquake, resulted in 7 fatalities.

The June 22nd, 2017 earthquake also follows a series of 16 events of M 4.0-5.5 on or near the subduction thrust interface about 150-250 km to the northwest, between late May 2017 and as recent as June 19, 2017. On June 14, 2017, a larger M 6.9 normal faulting, intermediate depth earthquake occurred within the subducting Cocos plate 175 km to the northwest of today’s event. The June 14th earthquake has been reported to have caused 5 fatalities.