Analysis of postseismic deformations after the 2010 Maule earthquake based on GPS data

The Chilean subduction zone is one of the most seismically active regions on Earth. Focal zones of earthquakes with magnitude M>8, registered in this region for the last 200 years, cover almost the entire length of the Chilean coast. In 2010 the Darwin seismic gap existing from 1835 between the focal zones of 1960 Great Chilean earthquake and the 1985 Valparaiso earthquake was interrupted by the Maule earthquake Mw = 8.8. We analyzed the data of 8 years of continuous observations at 27 sites of the Chilean GPS network in order to distinguish coseismic and postseismic deformations in the vicinity of the 2010 earthquake. The analysis of postseismic deformations is based on the ground displacement velocities estimated over 1-year intervals. We used the keyboard model of subduction zones [Lobkovsky and Baranov, 1984] combined with the model of viscoelastic relaxation in the asthenosphere and the upper mantle to explain the variety of motions observed in the region of Central Chile. We model viscoelastic relaxation caused by coseismic slip using the open-source software package VISCO1D of F. Pollitz. The coseismic displacements captured by the sites close to the epicenter of the 2010 event amounted to 1 to 3 meters, which characterizes the magnitude of the displacements of seismogenic blocks at the time of the earthquake. All the coseismic displacements are directed toward the ocean, which agrees well with the predicted movements of the blocks in the seismic stage of the seismic cycle. Data from the first two years after the 2010 event show attenuating site offsets toward the ocean over the whole Central Chile region which indicates passage of aftershock stage of the seismic cycle. Over the next 5 years the observed displacements can be explained by the process of restoring the stationary state of stress accumulation for seismogenic blocks in the frontal part of the subduction zone in combination with the continuing motion of the rear block with viscous asthenospheric flow. The duration of the viscoelastic relaxation process for the Maule earthquake is estimated to last for more than 15 years.