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Effects of seamount subduction on seismogenesis: comparative study of the 1992 Nicaragua and the 2002 Costa Rica earthquakes

AutorSallarès, Valentí ; Martínez-Loriente, S. ; Ranero, César R. ; Ruh, Jonas Bruno
Fecha de publicación18-abr-2017
CitaciónSubduction Interface Processes (SIP) meeting: (2017)
ResumenThe effect of seamount subduction on seismogenesis and, in particular, its role on earthquake nucleation, propagation and arrest, has been a long-standing matter of debate. Despite the large amount of work done in this subject, the question is far from being closed. While several studies show that seamounts can act as asperities where earthquakes ¿at least moderate magnitude ones- can nucleate, others suggest that they rather are physical barriers where rupture propagation stops. Examples showing one or another behavior abound, and different hypotheses have been proposed to explain the observations. In this work we compare (1) inter-plate geometry, velocity structure and velocity-derived fracturing degree at the base of the overriding plate, obtained from wide-angle seismic data inversion; (2) tectonic stresses and plastic strain along the inter-plate boundary obtained from 3D numerical modeling; and (3) epicenter location, moment rate and aftershock distribution, for two paradigmatic events: the Mw7.7, 1992 Nicaragua, and the Mw6.4, 2002 Osa Peninsula (Costa Rica) ones. The Nicaragua earthquake is composed of two sub-events, including a southern patch of equivalent magnitude Mw7.3 which, despite the different magnitudes, shares notable characteristics with the Costa Rica one. First, both nucleated at shallow depth and close to the trench, near the trailing edge of two well-imaged subducted seamounts. Second, the nucleation area and the highest moment release occur in a moderately fractured segment of the upper plate; which, as expected, coincides with a zone of large plastic strain and elevated tectonic overpressure. Despite these similarities, the Nicaragua event propagated updip to the trench, contributing substantially to the tsunami that hit the Nicaraguan coasts following the earthquake, whereas the Costa Rica one propagated downdip, so there was no tsunami and its impact was limited. Understanding the causes of these two contrasting behaviors despite their comparable genetic setting stands as an important question to evaluate their potential for seismic hazard.
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