A Mixed Seismic-Aseismic Stress Release Episode in a Weakly Coupled Subduction Zone in Northern Peru
Monday, 22 February 2016: 10:20 AM
Frederique Rolandone1, Juan Carlos Villegas Lanza2, Jean Mathieu Nocquet3,4, Martin Vallee5, Hernando Tavera6, Francis Bondoux7, Trong Dinh Tran8,9, Xavier Martin8 and Mohamed Chlieh4, (1)Univ Paris 06 CNRS UMR7193, Sorbonne Univ. ISTEP, Paris, France, (2)Instituto Geofísico del Perú, Unidad de Geodesia Espacial, Lima, Peru, (3)Instituto Geofísico, Escuela Politécnica Nacional, Quito, Ecuador, (4)Institut de Recherche pour le Développement - IRD, Valbonne, France, (5)Institut de Physique du Globe de Paris, Paris, France, (6)Instituto Geofísico del Perú, Lima, Peru, (7)GET Géosciences Environnement Toulouse, Observatoire Midi-Pyrénées, Toulouse, France, (8)Géoazur - Université Nice Sophia Antipolis, Valbonne, France, (9)National University of Civil Engineering, Civil Engineering, Hanoi, Vietnam
Abstract:
Transient aseismic slip geodetically documented in subduction zones show a great diversity of size, duration, temporal evolution of slip and associated seismic signature. Deep (30-50km) Slow Slip Events (SSE), lasting from weeks to months, often correlate with tremors, contributing at most to 0.1% of the total moment released. SSE detected in shallowly (<20km) coupled subduction zones show duration of days to weeks and are associated with intense microseismicity bursts, 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%. Here, we use geodetic and seismological observations to 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) and lasted 7 months. The synchronous seismicity involving Mw 5.8-6.0 events accounts for ~25% of the total moment release, equivalent to Mw 6.7. Unlike SSE which show a progressive acceleration of slip, transient slip started immediately after two earthquakes, before slowing down at logarithmic decay. The Mw 5.8 earthquake, which was followed by the largest acceleration and slip amount shares most characteristics of tsunami earthquakes and probably occurred in the conditionally stable part of the subduction interface. Considered 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. Synchronous aseismic slip and seismic swarms might define a stress release process distinct from SSE and earthquake/afterslip sequences.
