Diagenetic and shear-induced transitions of frictional strength of carbon-bearing faults and their implications for earthquake rupture dynamics in subduction zones.

Subduction-related diagenetic reactions affect fault strength and are thus important for understanding earthquake rupture dynamics in subduction zones. Carbonaceous material (CM) is found worldwide in active plate-boundary and intracontinental faults, yet the effect of its transformation on frictional strength and rupture dynamics remains unknown. We conducted high-velocity friction experiments together with organochemical analyses on CM in the form of lignite, bituminous coal, anthracite and graphite.

Role of Weak Materials in Earthquake Rupture Dynamics.

Weak materials in seismic slip zones are important in studies of earthquake mechanics. For instance, the exceptionally large slip during the 2011 Tohoku-Oki earthquake has been attributed to the presence of smectite in the fault zone. However, weak fault rocks cannot accumulate large amounts of elastic strain, which is thought to counter their ability to enhance seismic rupture.

Preservation of amorphous ultrafine material: A proposed proxy for slip during recent earthquakes on active faults.

The criteria for designating an "Active Fault" not only are important for understanding regional tectonics, but also are a paramount issue for assessing the earthquake risk of faults that are near important structures such as nuclear power plants. Here we propose a proxy, based on the preservation of amorphous ultrafine particles, to assess fault activity within the last millennium. X-ray diffraction data and electron microscope observations of samples from an active fault demonstrated the preservation of large amounts of amorphous ultrafine particles in two slip zones that last ruptured in 1596 and 1999, respectively.

Near-trench slip potential of megaquakes evaluated from fault properties and conditions.

Near-trench slip during large megathrust earthquakes (megaquakes) is an important factor in the generation of destructive tsunamis. We proposed a new approach to assessing the near-trench slip potential quantitatively by integrating laboratory-derived properties of fault materials and simulations of fault weakening and rupture propagation. Although the permeability of the sandy Nankai Trough materials are higher than that of the clayey materials from the Japan Trench, dynamic weakening by thermally pressurized fluid is greater at the Nankai Trough owing to higher friction, although initially overpressured fluid at the Nankai Trough restrains the fault weakening.

Effect of density-driven flow on the through-diffusion experiment.

Diffusion is one of the main mechanisms of solute transport in pore water of geologic media. The effective diffusion coefficient of a solute in a rock is usually measured by the through-diffusion experiment. However, in this experiment, the effect of advection, induced by density difference between dense aqueous solution and pure water, has not been considered.