Un séisme au Chili déclenche trémors et séismes lents au Mexique

Des chercheurs d’ISTerre voient leur travail mis en avant par les éditeurs du Journal of Geophysical Research, journal américain de référence en Géophysique pour leur travaux sur le déclenchement de trémors sismiques et de séismes lents au Mexique par le grand tremblement de terre du Chili de 2010. Ces résultats ont été obtenus dans le cadre de trois thèses préparées au laboratoire.

Zigone, D., et al. (2012), Triggering of tremors and slow slip event in Guerrero, Mexico, by the 2010 Mw 8.8 Maule, Chile, earthquake, J. Geophys. Res., 117, B09304, doi:10.1029/2012JB009160.

Resume :

Recently, scientists have observed that large earthquakes often trigger tremors in places far away, sometimes thousands of kilometers, from the epicenter. In a new study, researchers have now shown that a major earthquake in Chile could have also triggered "slow slips"—events during which large parts of continents move undetected, without leaving any trail in seismograms. Zigone et al. (2012) show that the Maule earthquake in Chile (Mw 8.8) on 27 February 2010 generated surface waves (S waves) that within hours induced tremors in the Guerero region of Mexico. They also observed that GPS stations in the region started moving southward coincident with the arrival times of the S waves and the starting of the seismic tremors. Both the tremors and the southward movement of GPS stations continued for several months following the earthquake. At depths of 70 km or more along the interface between plates—such as the zone where the Pacific plate is subducting below the American plate—heated and softened rocks slide past each easily without sticking. Nearer to the surface, friction between the moving plates causes rocks to stick, building up tension. Time and again the rocks slip suddenly, releasing the stress and causing an earthquake. Between the deeper ductile region and the rigid surface is a transition zone, where the rocks are only partly stuck ; friction is lower and stresses between plates build up only slightly and very slowly before snapping. The researchers suspect that the slip events in Mexico could indicate similar deformation processes at shallower depths. The observations provide an understanding of how slow slip processes, even at large distances from the epicenter of major earthquakes, could be redistributing localized stress.

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