RAPID: GPS Observations of Co- and Post-seismic Deformation in the Argentine Andes, Precordillera, and Sierras Pampeanas from the 16 Sep 2015, Mw 8.3, Illapel, Chile, Earthquake

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Scientists from the University of Memphis in collaboration with scientists from the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales will install 4 new continuous GPS stations and perform post-earthquake survey GPS measurements on 35 benchmarks in San Juan, Argentina. The measurements will be used to determine the mid-field co- seismic and post-seismic deformations of the September 16, 2015 Mw 8.3, megathrust earthquake offshore Illapel, Chile. These measurements, which capture the deformation field 100-400 km to the east of the earthquake, will complement similar activities in the immediate epicentral area in Chile from the Chilean Seismic Network. The mid-field to far-field signals are small, but significant as they are both poorly modeled and poorly understood in comparison to the much larger near-field signals. The mid- to far-field signals sample the response of the South America plate lithospheric stress guide, and the viscoelastic mantle wedge under the Andes in the west, and South America cratonic upper mantle to the east.The South America-Nazca plate boundary is unique as it is the only major convergent boundary where an almost complete aerial sampling of megathrust earthquake cycle deformation, from near- to far-field, can be observed in the upper plate side of a subduction system. Megathrust earthquakes along the South America-Nazca plate boundary produce large, rapid co-seismic deformations stretching across the whole continent. They also produce plate-wide post-seismic deformations that are initially faster than the inter-seismic deformations and can even surpass the co-seismic offset. These rapidly changing deformations may play an important role in tectonics by temporally concentrating aseismic deformation or triggering earthquakes. These signals decay with time, thus a rapid GPS deployment is necessary to capture the deformation signal before the signals decrease below the detection level. The proposed activity advances desired societal outcomes by providing data that would aid in determining regions of aftershocks that could be used in hazard mitigation efforts and would contribute to the understanding of earthquake hazard in the region. The project also contributes to enhanced infrastructure for research through the expansion of a GPS network and to adjustment of national geodetic reference frames.