International collaborative research groups (Japan, USA, China, Mexico) such as Kyoto University and Oregon State University conducted a reanalysis of the huge earthquake that occurred off the coast of Mexico in September 2017, and this earthquake was almost in the subducting plate. He showed the possibility that he had destroyed everything.As a result, the magnitude of similar earthquakes that occur around Japan may be larger than previously estimated.
In September 2017, a magnitude 9 earthquake struck off the coast of Chiapas, Mexico, causing damage to buildings and other areas due to the earthquake motion in Mexico, as well as tsunami damage along the coast.In the analysis immediately after the earthquake, the epicenter was considered to be a "normal fault type" earthquake that occurred inside the subducting plate, and that it occurred in the upper part of the subducting plate.
The research group reanalyzed the epicenter model of the earthquake using the seismic motion and crustal movement records observed in the surrounding area.As a result, it was found that the fault is much deeper than the conventional prediction by the stress field and temperature field inside the plate.The cause is said to be a decrease in the strength of deep rocks due to dehydration weakening.Along with the subduction of the plate, a normal fault type earthquake occurs on the sea side of the trench, which is the subduction zone, and seawater moves inside the plate along the fault (crack), and the hydrous minerals generated there It is thought that the subduction of the plate carried it to the deep part and dehydrated it from the minerals under the high temperature and high pressure environment, and the rock strength decreased, so that the destruction progressed to the deep part.
Even in the coastal areas of Japan, large earthquakes and accompanying tsunamis have occurred in the subducting plates such as the 1933 Showa Sanriku Earthquake.This study indicates that it is necessary to consider deeper rupture than previously predicted in estimating the magnitude of earthquakes that occur in subducting plates.Furthermore, it is said that it is necessary to review the scale of the assumed tsunami.
Paper information:[Nature Geoscience] Deep embrittlement and complete rupture of the lithosphere during the Mw 8.2 Tehuantepec earthquake
