Rapid mantle flow with power-law creep explains deformation after the 2011 Tohoku mega-quake

An apparatus for measuring nonlinear viscoelasticity of minerals at high temperature

We describe a high-temperature, uniaxial creep apparatus designed to investigate nonlinear attenuation of materials over a wide range of temperatures (25-1300 °C) using forced oscillations combined with a bias stress. This apparatus is primarily designed for investigation of minerals and rocks with high melting temperatures. An oscillatory compressional stress is used to determine attenuation and Young's modulus at frequencies of 10^-1-10² Hz and high stress amplitudes (>0.1 MPa). Large bias stresses are applied in addition to the oscillatory stresses such that attenuation tests are conducted simultaneously with the ongoing creep. The complex compliance of the apparatus was characterized by conducting calibration tests on orientated crystals of sapphire. The real part of the apparatus compliance exhibits a dependence on sample length and frequency, whereas the imaginary part is only dependent on frequency. The complex compliance is not dependent on the oscillation amplitude or the bias stress. We assess the accuracy and precision of this calibration by comparing measurements of the attenuation and Young's modulus of aluminum and acrylic to previously published values. We outline a set of criteria defining the conditions over which this apparatus can precisely determine the attenuation and Young's modulus of a sample based on the sample length and expected values of attenuation and Young's modulus.

Presence of interplate channel layer controls of slip during and after the 2011 Tohoku-Oki earthquake through the frictional characteristics

There are significant differences between the middle and southern segments of the Japan Trench in terms of the seismic and aseismic slips on the plate interface and seismic velocity structures. Although the large coseismic slip of the 2011 Tohoku-Oki earthquake was limited to the middle segment, the observed negative residual gravity anomaly area in the southern segment corresponds to the postseismic slip area of the Tohoku-Oki earthquake. A density distribution model can explain the different slip behaviours of the two segments by considering their structural differences. The model indicates that the plate interface in the south was covered with a thick channel layer, as indicated by seismic survey imaging, and this layer resulted in a residual gravity anomaly. Numerical simulations which assumed evident frictional heterogeneity caused by the layer in the south efficiently reproduced M9 earthquakes recurring only in the middle, followed by evident postseismic slips in the south. This study proposes that although the layer makes the megathrust less compliant to seismic slip, it promotes aseismic slips following the growth of seismic slips on the fault in an adjacent region.

Investigating a tsunamigenic megathrust earthquake in the Japan Trench

The 2011 Tohoku-oki earthquake occurred in the Japan Trench 10 years ago, where devastating earthquakes and tsunamis have repeatedly resulted from subduction of the Pacific plate. Densely instrumented seismic, geodetic, and tsunami observation networks precisely recorded the event, including seafloor observations. A large coseismic fault slip that unexpectedly extended to a shallow part of megathrust fault was documented. Strong lateral variations of the coseismic slip near the trench were recorded from marine geophysical studies, along with a possible cause of these variations. The seismic activities in east Japan are still higher than those before the earthquake, and crustal deformation is still occurring. Although the recurrence probability of a great earthquake (magnitude = ~9) in the Japan Trench in the near future is very low, a large normal fault earthquake seaward of the Japan Trench is a concerning possibility.

Coupled afterslip and transient mantle flow after the 2011 Tohoku earthquake

Modeling of postseismic deformation following great earthquakes has revealed the viscous structure of the mantle and the frictional properties of the fault interface. However, for giant megathrust events, viscoelastic flow and afterslip mechanically interplay with each other during the postseismic period. We explore the role of afterslip and viscoelastic relaxation and their interaction in the aftermath of the 2011 M _w (moment magnitude) 9.0 Tohoku earthquake based on a detailed model analysis of the postseismic deformation with laterally varying, experimentally constrained, rock rheology. Mechanical coupling between viscoelastic relaxation and afterslip notably modifies both the afterslip distribution and surface deformation. Thus, we highlight the importance of addressing mechanical coupling for long-term studies of postseismic relaxation, especially in the context of the geodynamics of the Japan trench across the seismic cycle.