Analysis of surface deformations related to the 2010 Maule earthquake
based on GPS data
Abstract
The Chilean subduction zone is one of the most seismically active
regions on Earth, due to the shallow depth of the seismogenic zone in
combination with the high coupling coefficients and high plate
convergence rate. On February 27, 2010, the Maule earthquake, which is
one of the strongest instrumentally registered megathrust earthquakes,
occurred in Darwin seismic gap – a seismically calm zone existed near
the coast of Chile since 1835. We use the keyboard model of generation
of strong subduction earthquakes [Lobkovky et al., 1991] to analyze
the peculiarities of seismic deformation cycle (SDC) related to the
Darwin seismic gap and the 2010 earthquake. Keyboard structure of the
South American continental margin near the source zone of the Maule
earthquake is confirmed by seismological and geological data. Using of
keyboard model allows us to associate interseismic, coseismic and
postseismic deformations observed by satellite geodesy with the action
of particular geodynamic processes and, therefore, to study their
features. To achieve this aim, we analyze the data of almost 10 years of
continuous observations at 76 stations of the Chilean GPS network
deployed along the source zone of the 2010 Maule earthquake. The
analysis of variations in surface deformation fields is based on
displacement rates fields of GPS stations estimated over 1-year
intervals. On the basis of registered coseismic displacements we
construct a model of slip distribution in the source zone of the Maule
earthquake and determine the magnitudes of instantaneous shifts of
seismogenic blocks towards the ocean, which reached 1-3 meters. In the
first two years after the 2010 earthquake GPS stations shift toward the
ocean over the whole Central Chile region, which indicates passing of
aftershock stage of the SDC. Over the next 7 years of observations, the
observed displacements can be mainly 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 displacement of the rear massif by a viscous
asthenospheric flow. To assess the time of transition of seismogenic
zone to stationary state of accumulation of elastic stresses we
construct models of frictional afterslip and viscoelastic relaxation in
the asthenosphere. The durations of the afterslip and viscoelastic
relaxation processes for the Maule earthquake are according to our
estimates about half a year and more than 15 years respectively.
Understanding of the features of the SDC plays a significant role in the
seismic hazard assessment of the Maule and Biobio regions of Chile.