A Slow Slip Event and synchronous seismicity in the Northern Peru subduction zone

Preliminary results of this study have been presented in the AGU Fall Meeting 2012 in San Francisco.

In this study we report the observations of a Slow Slip Event (SSE) and a synchronous seismicity occurred in 2009 along a segment of the Nazca/South America subduction zone in northern Peru. The SSE event started in early 2009 and lasted 7 months, involving a maximum trenchward displacement of 14 mm recorded at the permanent station in the Bayovar Peninsula. Modeling of the cumulative surface displacements field show that a shallow patch of of the megathrust interface has slipped up to 45 mm leading to and eq. moment release of an earthquake of Mw=6.7. During this period and abrupt increment of the seismicity rate occurred in the same area. However the cumulative seismic moment of the seismicity only accounts for about 35% of the total geodetic moment released. This observation constitutes one of the first that correlates rupture characteristics with aseismic slip in a subduction zone. I general terms, our results suggest a model where the anatomy of the subduction interface is constituted  of small to moderate-size isolated patches of velocity weakening material embedded in a much larger velocity strengthening area which promotes aseismic slip or large post-seismic slip once the small asperities are ruptured.

Authors: Villegas Lanza JC., Nocquet J-M., Chlieh M., Vallée M., Tavera H. and Rolandone F.
IGP, Geoazur, IRD and ISTEP