Frictional behavior and its seismological implications within thrusts in the shallow portion of an accretionary prism

The Emi Group in the Boso accretionary complex is reported to have experienced a relatively shallow burial depth, approximately 1-4 km below the sea floor at low temperature (50-75 °C), indicating that the group passed through or around the upper portion of the seismogenic zone. Two representative thrusts in the group were recognized as products of deformations in the setting. Frictional experiments using the powder samples from the fault zones showed the frictional behavior of velocity hardening under the wet condition with 20 MPa and 40 MPa normal stresses. Microstructures within the thrusts exhibited pervasive deformation with composite planer fabrics. This results that the shallow portion of the thrust at the base of the accretionary prism is aseismic with stable sliding.