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