The role of Earthquake Prediction Research Center (EPRC) is to promote national or international research projects on earthquake prediction. In 2000, the coordinating committee of the Earthquake Prediction Research Committee was established at EPRC.

1. Laboratory and numerical experiments on asperity and aseismic slip area

Slip experiments using large granite blocks are performed by inserting a thin Teflon sheet along half section of the fault. In the velocity-strengthening area, the stress rapidly increases during the dynamic event, and then afterslip occurs with gradual stress relaxation. At a point sufficiently remote from the asperity, only afterslip occurs without coseismic slip. The numerical simulation quantitatively reproduces the slip behavior found in the laboratory experiment.

Changes in shear stress (left) and displacement (right).

2. Deformation Process of Island Arc Crust and Active Fault Researches

Cooperated by other universities and related institutes, we plan to conduct a large field experiment surrounding the Atotsugawa Fault. The area suffers from rapid strain accumulation so that the clarification of stress accumulation process is important for help understand the mechanism of earthquake generation. We plan to deploy seismometers, geomagnetic instruments, and GPS receivers. We also conduct controlled seismic exploration experiments.

Site plots for long-term earthquake monitoring in and around the Atotsugawa fault.

3. Geoelectromagnetic observations and resistivity structure

We are promoting cooperative field experiments for electromagnetic monitoring and resistivity structure determination, and try to elucidate physical process which lies between respective fundamental processes and the observations. A figure shows crustal water content estimated from the resistivity structure beneath Tohoku backarc area, based on results of laboratory experiments for rock and water resistivity and crustal temperature structure estimated from surface heat flow distribution.

Water content distribution in the crust, which is estimated from 2-D resistivity cross section beneath active Tohoku backarc area. Also shown are seismicity data (circles), S-wave reflectors (squares) & P-wave scatterers (stars), seismic reflection result and seismic refraction result.

4. GPS Researches on Crustal Deformation Process

Japanese University Consortium for GPS Research (JUNCO) centered at EPRC conducted temporal GPS observations after the 2003 Tokachi-oki Earthquake to monitor post-seismic crustal deformation. Analysis of GEONET data showed transient deformation in Hokkaido. Area of post-seismic slip along the plate interface was found to be complementally to the area of co-seismic displacements.

Cumulative slip in the 30 days following the earthquake. Arrows show the direction and magnitude of slip of the upper plate. Small circles are aftershocks (M>4) with one nodal plane parallel to the mainshock rupture. Coseismic slip contours are also shown.

5. Numerical simulation of seismic cycles

We conduct numerical simulations of seismic cycles using rate and state-dependent friction laws. Recently found episodic aseismic slip events can also be simulated with the model. A critical fault size for the occurrence of seismic slip can be defined as a function of frictional constitutive parameters. Episodic aseismic slip events occur when the patch size with velocity-weakening frictional property is comparable with the critical fault size.

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