M 8.1 Earthquake Strikes Southern Mexico

M 8.1 Earthquake Strikes Southern Mexico

  • EOS News
08 Sep 2017

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This maps shows the distribution of earthquakes along the Middle America Trench, including today’s earthquake and the megathrust earthquake in 1985 (Source: Wang Xin, 2017)

A major earthquake struck the coast of southern Mexico near the Mexican-Guatemalan border on 8 September 2017 at approximately 12:50 pm (Singapore time). According to the United States Geological Survey (USGS) and the GeoForschungsZentrum (GFZ), this magnitude-8.1 earthquake occurred at a depth of about 70 kilometres near the triple junction where the North American, Caribbean, and Cocos plates meet. The North American plate slides past the Caribbean plate, while the Cocos plate subducts beneath the North American and Caribbean plates. Today’s earthquake’s epicentre was located at a part of the Cocos plate that has already been subducted with the rate about 7.5 centimetres per year.

Based on the preliminary information provided by USGS and GFZ, this M 8.1 quake is likely a normal-faulting event occurring within the subducted slab of the Cocos plate. In 1985, just a few hundred kilometres north of this event, a M 8.0 earthquake shook Mexico City. Although today’s earthquake has a similar magnitude to its 1985 counterpart, its cause is very different. The 1985 earthquake occurred because of a sudden ‘unlocking’ at the Middle American megathrust interface – the contacting surface of the Cocos plate and the North American and Caribbean plates. Today’s earthquake was likely caused by the sudden breaking of part of the Cocos plate that has already been subducted.

Although today’s event is not caused by a shallow megathrust rupture, the kind that is typically associated with tsunamis, it is still possible that this event could generate tsunami waves which would affect the coast of southern Mexico. The risk of its tsunami waves affecting Southeast and East Asia, however, is relatively low because the rupture will likely send tsunami waves into the southern part of the Pacific Ocean.

Although today’s earthquake occurred just as Super Hurricane Irma approaches the Caribbean Islands, the two events are likely unrelated. Hurricanes and typhoons can cause changes in atmospheric pressure or erosions from heavy rainfall, which can lead to the release of tectonic stress accumulated in the shallow part of the earth’s crust. This, however, only applies to the area within the hurricane’s path. The significant distance between Hurricane Irma and today’s earthquake further suggests that the two events are separate.