SourceURL:file://localhost/Users/socquet/Auboulot/congres/socquetAGU2014.doc Geodetic coupling in the North Chile - South Peru seismic gap: new insights from GPS measurements in Peru

Wednesday, 17 December 2014: 4:00 PM
Anne Socquet1, Nathalie Cotte2, Edmundo O Norabuena3, Wendy Quiroz3, Jorge Jara1, Jesus Pina-Valdes1, Mohamed Chlieh4, Daniel Carrizo5, Marta Bejar Pizarro6 and Marianne Metois7, (1)ISTerre Institute of Earth Sciences, Saint Martin d'Hères, France, (2)CNRS, Paris Cedex 16, France, (3)Instituto Geofísico del Perú, Lima, Peru, (4)Geoazur, Valbonne, France, (5)University of Chile, AMTC, Santiago, Chile, (6)Instituto Geologico Minero Espana, Madrid, Spain, (7)National Institute of Geophysics and Volcanology, Rome, Italy

The subduction zone at the latitude of the Central Andes did not experience a Mw>8.5 earthquake since the 19thcentury, and forms a ~500km long seismic gap in North Chile - South Peru.

Understanding the factors that limit the extent of seismic ruptures is crucial for risk mitigation and for understanding physical processes that govern the behavior of seismogenic faults. It appears crucial to evaluate interseismic coupling and its spatial variation in seismic gaps to assess seismic potential.

Recent geodetic studies combining continuous and campaign GPS measurements as well as InSAR measurements showed that the subduction interface in north Chile, was accumulating interseismic elastic strain, likely to rebound into a large megathrust Earthquake.

A Mw8.2 earthquake occurred on the 1st of April 2014 in this seismic gap, in front of Pisagua (North Chile), ~150 km south of the Chile-Peru Border. In spite of its already large magnitude, that earthquake was smaller expected in the area, and has most probably increased the stress in the unbroken segments at both edges. Most of accumulated strain remains to be relaxed in the North Chile-South Peru seismic gap. Here we propose to present a first assessment of the interseismic loading in the South Peru part of the seismic gap, at the northern extremity of Pisagua Earthquake, where it is poorly known.

In south Peru, over an area of 500 x 250 km, 33 campaign markers have been installed and measured in June 2012. This network has been partially remeasured in June 2013 and April 2014 (after Mw8.2 Pisagua Eaquake). These measurements provide us with an estimate of the Pre-Pisagua-Earthquake coupling, and the co-seismic static displacements. These displacements are combined together with the ones of previous studies that occurred in North Chile and provide a unique and dense velocity field spreading through the Chile Peru border. In particular this provides a unique assessment on the pre-earthquake interseismic coupling at the latitude of the Arica bend, often described as a seismic barrier, and therefore expected to slip aseismically. Results of the GPS derived interseismic segmentation are compared with the seimicity and geomorphic features in the area.