Rheological profile across the NE Japan interplate megathrust in the source region of the 2011 Mw9.0 Tohoku-oki earthquake

Abstract

A strength profile across the NE Japan interplate megathrust was constructed in the source region of the 2011 Tohoku-oki earthquake (M w 9.0) using friction, fracturing, and ductile flow data of the oceanic crustal materials obtained from laboratory experiments. The depth-dependent changes in pressure, temperature, and pore fluid pressure were incorporated into a model. The large tsunamigenic slips during the M9 event can be explained by a large gradient in fault strength on the up-dip side of the M9 hypocenter, which was located 17 to 18 km beneath sea level. A large stress drop (approximately 80 MPa) induced by the collapse of a subducted seamount possibly triggered the M9 earthquake. In the deep (>35 km) part of the thrust fault, where M7-class Miyagi-oki earthquakes have repeatedly occurred, plastic deformation occurs in siliceous rocks but not in gabbroic rocks. Thus, the asperity associated with the M7-class earthquakes was most likely a gabbroic body, such as a broken seamount, surrounded by siliceous sedimentary rocks. The conditionally stable nature of the surrounding region can be explained by the frictional behavior of wet quartz in the brittle-ductile transition zone. In contrast to the deep M7-class asperity, the M9 asperity (i.e., a region that was strongly coupled before the M9 Tohoku-oki earthquake) extended to a large area of the plate interface because shear strength is relatively insensitive to lithological variation at intermediate depths. However, the along-arc extension of the M9 asperity was constrained by fluid-rich regions on the plate interface.

Frictional Properties of Simulated Chlorite Gouge at Hydrothermal Conditions: Implications for Subduction Megathrusts

“…At shallow parts in a subduction zone the strength of megathrust faults is largely controlled by the upper part of the subducting plate, which in the case of subducting oceanic plate consists of clay minerals and micas derived from oceanic sediments (e.g., Shimizu, ). However, at greater depths, megathrust faults penetrate basic metamorphic rocks, and specifically under greenschist‐facies conditions the fault core is likely to be enriched in chlorite.…”

Experimental grain growth of quartz aggregates under wet conditions and its application to deformation in nature

“…However, these studies proved that the dehydration reaction of talc does not affect the water environment in Pt capsules including samples and water. Water fugacities at given conditions of pressure and temperature were calculated from the molar volume and the equation of state of pure water using the data of Pitzer and Sterner (1994) and Sterner and Pitzer (1994).…”

Theoretical derivation of flow laws for quartz dislocation creep: Comparisons with experimental creep data and extrapolation to natural conditions using water fugacity corrections

“…Estimates of the strength of quartz under deformation conditions appropriate to the continental crust. The light blue lines show frictional strengths of fault zones calculated with a modified Byerlee's law for hydrothermal conditions [ Shimizu , ]. Most optimally oriented faults in the continental crust, which has a density of 2.75 g/cm 3 and a hydrostatic pore pressure gradient, are assumed faults.…”