September 8, 2017

expert reaction to the Mexico earthquake

An earthquake that measured 8.2  struck in the Pacific, about 87km (54 miles) south-west of Pijijiapan.

Dr Carmen Solana, Senior Lecturer at the University of Portsmouth, said:

“Offshore the west coast of Mexico runs a huge ‘scar’ where two different tectonics plates meet and this collision is what causes earthquakes in the area. Because Mexico City is built on soft soil, it shakes vigorously, even when the earthquakes occur far away.”

Prof. David Rothery, Professor of Planetary Geosciences at The Open University, said:

“This morning’s (04:49 GMT) earthquake off the coast of Mexico occurred where the floor of the Pacific Ocean (here the Cocos plate) is being drawn northeastwards below the edge of the North American plate at an average age of nearly 8cm per year. The plates don’t slip smoothly past each other. Instead the deformation builds up by flexing and bending until enough stress has been built up to release the blockage allowing many years’ worth of movement to occur in a few seconds. This is referred to as “stick-slip”. This particular earthquake measured magnitude 8.1 on the Richter scale, which is typically big enough to signify several metres displacement on a more than 100 km long length of fault. Being below the sea, the sudden jerking of the seabed has the potential to cause a tsunami.

“Fortunately the initial rupture in this case was at a depth of about 70 km, which is sufficiently deep to lessen the surface movement, thus weakening both the tsunami and the strength of the ground shaking felt by those nearby on land. However the shaking was felt in Mexico City some hundreds of km away, and I would expect some damage to poorly constructed buildings in the nearest town such as Pijijlapan, Paredon and Tuxtla Gutierrez.

“The Pacific Tsunami Warning Center has issued a warning of tsunami waves of up to 3 metres on the south coast of Mexico, and up to a metre on many island coastlines across the Pacific. The effect of tsunami waves coming ashore is strongly dependent on the local undersea topography, so local damage may be very variable.

“There is absolutely no link between the causes of this earthquake and the tropical storms currently affecting the Caribbean.

“On average there is only about one earthquake exceeding magnitude 8 per year.  The largest previously this year was a magnitude 7.9 near Papua New Guinea on 22 January.  There was no magnitude 8 earthquake in 2016. Today’s earthquake is the largest since a magnitude 8.3 earthquake off the coast of Chile 16 Sept 2015. The earthquake that caused the 9 March 2011 tsunami in Japan measured magnitude 9.1, releasing about 30 times more energy than today’s earthquake.”

Declared interests

None declared