A new GPS velocity field from central to northern Peru

Fast subduction of the oceanic Nazca plate beneath the South American continent induces large earthquakes with a carateristic repeat time of 100-150 years in Chile and southern Peru (Compte and Pardo, 1991; Dorbath, et al., 1990; Nishenko, 1991). Previous studies of the interseismic deformation along the Andean subduction using GPS and/or InSAR have shown a current significant level of locking of the interplate interface all along the margin. However, the overall picture is still missing information from thenlatitude 10S (North of Lima, Peru) to 2S (North of Guayaquil, Ecuador). In that area, no large earthquake has been for the last three centuries (Dorbath, et al., 1990; Kelleher, 1972), suggesting on one hand that this portion may be freely aseismically slipping. On the other hand, the factors usually assumed to control the level of locking (convergence rate, age of the ocean floor, presence of sediments along the trench, Ruff and Tichelaar, 1996) are not very different from the adjacent segments where large earthquakes have occurred in the past. The question posed is: has the plate interface accumulated large stress during the last centuries possibly triggering a giant earthquake in the next years or is it aseismically slipping?. We present new GPS results for central to northern Peru resulting from a combination of survey-mode GPS and continuos GPS measurements to answer this question. Our solutions spans the 2007-2010 period (4 years), and includes CGPS sites from the LISN project (http://jro.igp.gob.pe/lisn/) dedicated to monitor the ionosphere, from the ADN project and IGS global stations. We first asses the quality of our time series and discuss the uncertainty of velocities estimates after 2-3 years of data. We first note that the repeatabilities obtained strongly depend of the type of monumentation and equipment used for the vertical component for sites from the LISN network. Nonetheless, for velocity estimates, the agreement with sites showing best repeatabilities are usually within 1-3 mm/yr. Finally, we preliminary conclude that low coupling is found from central Peru at about 8S to the border with Ecuador. Very high coupling is found further south around LIma. We will present preliminary models of coupling based on these results. To be presented in the EGU 2011 Vienna (Villegas JC, et., al 2011)