Observation of the Seismogenic Fault in the Okitsu Melange, Shimanto Accretionary Complex and Stick Slip of Mineral Cementation of Shear Experiment

Abstract

The seismogenic fault in the Okitsu Melange, Shimanto accretionary complex, Shikoku is characterized by repeated rapid slips with a pseudotachylyte formation and a concentration of vein minerals. The Okitsu Melange is composed of duplex structure of imbricated oceanic stratigraphic sequence, and the seismogenic fault is emplaced at the roof thrust of the duplex structure. Comparable fault along the seismogenic roof thrust of the duplex structure was found at the present Nankai trough, and vein mineral precipitation is expected from the fluid flow along the fault.
Some of the clasts of cataclacite were supported by a vein mineral matrix of euhedral ankerite and quartz crystals. This occurrence of vein minerals may indicate rapid precipitation due to fluid flow of super saturation with vein minerals along the fault zone. The shear strengthening with time and the stick slips were recognized by the block-slider analogue experiments which consisted of the chilled slid with ice and hot water saturated with alum on the shear surface. The result of the experiment indicates that the vein mineral precipitation make stick slip the fault.