Upper plate deformation measured by GPS in the Coquimbo Gap, Chile

Christophe Vigny , Alain Rudloff , Jean-Claude Ruegg , Raul Madariaga , Jaime Campos , Manuel Alvarez

Since the M=7.3 Punitaqui earthquake in 1997, the area between 30°S and 32°S (Coquimbo-Illapel section) of the Chilean subduction has been the locus of a decennial seismic swarm. A dense network of 30+ benchmarks have been installed in this area and surveyed six times with high precision GPS over the last three years. Surface deformation here is compatible with elastic loading due to partial locking on the subduction interface at depth. Here we show that in this area, only 40% to 45% of the total convergence rate between Nazca and South America plates gives way to accumulation of elastic deformation in the upper plate, the remaining 60% to 55% being dissipated by free or aseismic slip, the cumulative slip due to the seismic swarm explaining no more than 1/3 to 1/4 of it. We also find that the accumulation decreases northward, to reach almost zero around 30°S (La Serena –Tongoy). Whether this is a steady state or only a transient pattern (a steady decrease of coupling) is not clear since our measurements span only 3 years and since early measurements 10 years ago were sparse and differ only marginally from ours.

Mots clés: Physical Sciences

Christophe Vigny, Alain Rudloff, Jean-Claude Ruegg, Raul Madariaga, Jaime Campos, et al.. Upper plate deformation measured by GPS in the Coquimbo Gap, Chile. Physics of the Earth and Planetary Interiors, 2009, 175 (1-2), pp.86. ⟨10.1016/j.pepi.2008.02.013⟩. ⟨hal-00533422⟩