S31A-2735
A Slow Slip and Seismic Swarm Sequence in a Weakly Coupled Subduction Zone in Northern Peru
Wednesday, 16 December 2015
Poster Hall (Moscone South)
Juan Carlos Villegas Lanza1, Jean-Mathieu Nocquet2, Frederique Rolandone3, Martin Vallee4, Hernando Tavera5, Francis Bondoux6, Trong Dinh Tran2,7, Xavier Martin2 and Mohamed Chlieh8, (1)Instituto Geofísico del Perú, Unidad de Geodesia Espacial, Lima, Peru, (2)Géoazur - Université Nice Sophia Antipolis, Valbonne, France, (3)University Pierre and Marie Curie Paris VI, istep, Paris, France, (4)Institut de Physique du Globe de Paris, Paris, France, (5)Instituto Geofísico del Perú, Lima, Peru, (6)GET Géosciences Environnement Toulouse, Observatoire Midi-Pyrénées, Toulouse, France, (7)National University of Civil Engineering, Civil Engineering, Hanoi, Vietnam, (8)Geoazur, Valbonne, France
Abstract:
Processes releasing the stress accumulated along subduction megathrusts show a great diversity in their seismic and aseismic signatures, and in the ratio between the two modes of slip. Deep (30-50km) Slow Slip Events (SSE) are often accompanied by tremors, accounting for less than 0.1% of the total moment release. Shallow (<20km) SSE show synchronous intense microseismicity, whose contribution is 0.1 to a few percent of the total moment release. At the other end of the spectrum, earthquake-afterslip sequences usually show an aseismic/seismic moment release ratio between 20 to 100%, with some unusual cases reaching 400%. Here we document a seismic/aseismic sequence along the weakly coupled northern Peru subduction zone that departs from previously observed categories. The sequence took place at shallow depth (<25km), lasted 7 months, and the synchronous seismicity accounts for ~25% of the total moment release equivalent to Mw 6.7. Unlike SSE which show a progressive acceleration of slip, rapid transient slip started immediately after two earthquakes, before slowing down at logarithmic decay, similarly to the afterslip following large earthquakes. The earthquake which triggered the largest acceleration and slip amount shares most characteristics of tsunami earthquakes and probably occurred in the conditionally stable part of the subduction interface. Taken separately, the moment released by the transient aseismic slip following this latter earthquake is >1000% of the co-seismic moment and the observed transient slip cannot be explained by classical models of afterslip. This sequence suggests that Seismic Swarms that are commonly observed at subduction megathrusts actually release much more stress than indicated by their cumulative seismic moment.
