On the Origin of Postseismic Deformation Processes in the Region of the Maule, Chile Earthquake of February 27, 2010
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he Origin of Postseismic Deformation Processes in the Region of the Maule, Chile Earthquake of February 27, 2010 V. O. Mikhailova, b, *, E. P. Timoshkinaa, V. B. Smirnova, b, S. A. Khairetdinova, and P. N. Dmitrieva a
Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, 123242 Russia bFaculty of Physics, Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received May 27, 2020; revised June 7, 2020; accepted June 9, 2020
Abstract—For the first time, we present a rupture surface model of the 2010 Maule earthquake, Chile, based on the combination of satellite geodesy, InSAR, and satellite gravimetry data. The regularization method used for constructing the model allowed us to find a uniform displacement field on rupture surface provided that a slip rake is close to a given one. On average, the displacements on the rupture surface are about 5 m with a maximum displacement of 13.1 m. The rupture zone extends south of the Arauco Peninsula and reaches a depth of 42 km along the plate surface. Using the constructed seismic rupture model, we have modeled the process of viscoelastic relaxation of stresses that emerged in the lithosphere and upper mantle as a result of the earthquake in order to estimate the contribution of this process in the observed postseismic displacements. Surface displacement velocities mainly depend on the viscosity value adopted for the asthenosphere. The comparison of the calculated and measured displacements at low viscosity of the asthenosphere shows that when the displacements are measured far from rupture surface as it is the case with the ocean– ocean subduction zone earthquakes, the observed displacements can be explained by the process of viscoelastic relaxation with a low viscosity of the asthenosphere. In the cases when there are data on the displacements above rupture surface, e.g., for the 2010 Maule earthquake, explaining the observed displacements by stress relaxation process in the near zone of the rupture is not possible at any viscosity: the displacements substantially differ both in amplitude and direction. At the same time, the postseismic creep models fairly well agree with the entire set of the existing data. Therefore, there is no need to accept the hypothesis of a low-viscous asthenosphere in the region of the 2010 Maule earthquake. Previously, we arrived at the similar conclusion considering the modeling results for the Sumatran earthquake of 2004, Simushir earthquakes of 2006, and a number of other large earthquakes in the subduction zones. Keywords: Maule, Chile, earthquake on February 27, 2010, GPS, InSAR, gravity models, GRACE satellites, rupture surface model, viscoelastic stress relaxation, postseismic creep DOI: 10.1134/S106935132006004X
INTRODUCTION The large earthquakes that occurred at the beginning of the 21st century have been thoroughly studied using, modern ground-based and satellite measurements at global and local seismic networks, at temporary and permanent GPS sites. Besides, satellite interferometric synthetic ape
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