MW 8.2 SEPTEMBER 8, 2017 MEXICO EARTHQUAKE: STATIC STRESS INCREASE, AFTERSHOCKS AND ITS RELATION TO THE GRAVITY SIGNAL

SILVANA SPAGNOTTO; ALVAREZ ORLANDO; ANDRES FOLGUERA

Kunming, Yunnan Province

Simposio; International Symposium on Geodesy and Geodynamics, ISGG2018-Tectonics, earthquake and Geohazards; 2018

Institute of Seismology, China Earthquake Administration

A Mw 8.2 earthquake affected on September 8, 2017 the Cocos plate beneath the Caribbean plate next to the transform contact with the North American plate across the Tehuantepec gap, one of the two gaps that exist along the Mexican subduction zone offshore Chiapas. The epicenter occurred at a depth of 47 km and was associated with a highly steep normal fault parallel to the trench. The origin can be related to slab pull forces, dehydration processes and reactivation of outer rise faults. This earthquake produced positive changes in the Coulomb static, which would favor the development of thrust displacements along the interplate contact across the Tehuantepec gap instead of liberating tensions accumulated on it for decades. In the case that stresses were not released steadily in the next time, a thrusting-related event with a magnitude of Mw 7.9 or higher could be expected after the September 8, 2017 Chiapas earthquake. However, the differential weight of the forearc offshore (that contains a region with a high positive gravity gradient) could inhibit rupture propagation to the coast precluding higher magnitudes. Combined and satellite only Earth gravity field models show a highly heterogeneous density structure along the forearc of the