The United States Geological Survey recorded a Magnitude 8.5 Earthquake at a depth of 19.8 km, off the south coast of Chiapas State, Mexico, slightly before 9.30 am local time (clightly before 3.20 pm GMT) on Monday 22 February 2021. There are no reports of any damage or casualties associated with this event, but people have reported feeling it in Puerto de San Benito on the coast of Chiapas State.
The approximate location of the 22 February 2021 Chiapas State Earthquake. USGS.
Mexico is located on the southernmost part of the North American Plate.
To the south, along the Middle American Trench, which lies off the
southern coast off Mexico, the Cocos Plate is being subducted under the
North American Plate, passing under southern Mexico as it sinks into the
Earth. Guatemala
is located on the southern part of the Caribbean Plate, close to its
boundary with the Cocos Plate, which underlies part of the east Pacific.
The Cocos Plate is being pushed northwards by expansion of the crust
along the East Pacific Rise, and is subducted beneath the Caribbean
Plate along the Middle American Trench. This is not a smooth process, and the plates frequently stick
together then break apart as the pressure builds up, causing Earthquakes
on the process.
The Cocos Plate is thought to have formed about 23 million years ago,
when the Farallon Plate, an ancient tectonic plate underlying the East
Pacific, split in two, forming the Cocos Plate to the north and the
Nazca Plate to the south. Then, roughly 10 million years ago, the
northwesternmost part of the Cocos Plate split of to form the Rivera
Plate, south of Beja California.
In a paper published in the Journal of Geophysical Research, in 2012, a team led by Igor Stubailo of the Department of Earth and Space Sciences at the University of California Los Angeles, published a model of the subduction zone beneath Mexico using data from seismic monitoring stations belonging to the Mesoamerican Seismic Experiment, the Network of Autonomously Recording Seismographs, the USArray, Mapping the Rivera Subduction Zone and the Mexican Servicio Sismologico Nacional.
The seismic monitoring stations were able to monitor not just
Earthquakes in Mexico, but also Earthquakes in other parts of the world,
monitoring the rate at which compression waves from these quakes moved
through the rocks beneath Mexico, and how the structure of the rocks
altered the movement of these waves.
Based upon the results from these monitoring stations, Stubailo et al.
came to the conclusion that the Cocos Plate was split into two beneath
Mexico, and that the two plates are subducting at different angles, one
steep and one shallow. Since the rate at which a plate melts reflects
its depth within the Earth, the steeper angled plate melts much closer
to the subduction zone than the shallower angled plate, splitting the
Trans-Mexican Volcanic Belt into sections above the different segments
of the Cocos Plate, and causing it to apparently curve away from the
subduction zone.
See also...
