Main features of the formation and development of the fault zone of the 2011 Tohoku earthquake derived from GPS data

Abstract

<p>On March 11, 2011, the strongest (Mw = 9.0) Tohoku earthquake occurred in northeastern Japan, completing a seismic cycle that lasted nearly 1200 years. We analyzed an extensive set of satellite geodetic, seismological and geological data to determine the geometry of the fault zone, to build an ensemble of models of distributed interseismic, coseismic and postseismic displacements in the source zone, and to study the possible effect of structural inhomogeneities of the medium on the accumulation and release of elastic stresses.</p><p>We found that the mechanical coupling immediately before the Tohoku earthquake was relatively high. The interplate coupling coefficient reaches its maximum values near the trench, which could be one of the factors that led to the occurrence of such a devastating tsunami. Near the lower edge of the future fault zone, we found areas of weakened coupling, which probably prevented the downward propagation of the seismic rupture. The area of maximum displacements in the seismic source is, as expected, located in the upper part of the fault zone. The areas of the greatest displacements in the effective postseismic source are concentrated near the lower edge of the seismic rupture, apparently marking the areas where elastic stresses were not released during the earthquake.</p><p>Asthenospheric viscosity is one of the key parameters governing the postseismic processes in the vicinity of the source zone of the large subduction earthquake. The study of postseismic deformations caused by the Tohoku earthquake allows us to establish some limitations on the mechanical properties of the asthenosphere under the Japan islands. Our estimate of the effective Maxwell viscosity of the asthenosphere in northeastern Japan is about ten times lower than the average value established for continental subduction zones. According to our forecast, based on the assumption of the constant effective viscosity of the asthenosphere, the prevalence of postseismic displacements in the vicinity of the source will cease approximately 30 years after the Tohoku earthquake.</p><p>An integral approach to studying the features of the seismic cycle in subduction zones allows us to establish the relationship between geodynamic processes at different stages of the cycle and to study the influence of regional characteristics of the medium.</p><p>This study was supported by Russian Science Foundation (project 20–17-00140).</p>