Wednesday 29 March 2017

Magnitude 5.7 Earthquake beneath the Gulf of California.

The United States Geological Survey recorded a Magnitude 5.7 Earthquake at a depth of 10 km beneath the Gulf of California, roughly 74 km off the coast of Sinaloa State, Mexico, at about 8.15 am local time (about 3.15 pm GMT) on Wednesday 29 March 2017. Although this was a large, shallow quake, and therefore potentially dangerous, it occurred some distance offshore, and while there are reports of it being felt over a wide area of Baja California Sur, Sonora and Sinaloa states, there are no reports of any damage or injuries arising from this event.

The approximate location of the 29 March 2017 Gulf of California Earthquake. USGS.

The boundary between the Pacific and North American Plates runs beneath the Gulf of California, with Beja California lying on the Pacific Plate and the Mexican mainland on the North American. The Pacific Plate is moving northwest with regard to the North American Plate, while the North American Plate is moving southeast relative to the Pacific Plate. This creates a transform plate margin along the centre of the Gulf of California, as the two plates slide past one-another, a margin that continues northward under California as the San Andreas Fault. The plates do not move past one-another smoothly, but continuously stick together then break apart as the pressure builds up, leading to regular Earthquakes beneath the Gulf of California and in the surrounding area.

 Map showing the relative movement of the Pacific and North American Plates, and the fault system beneath the Gulf of California. Monterey Bay Aquarium.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

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