プレート沈み込み帯における地震波低速度層―地震発生への影響と探査法

low-velocity zonesubduction zoneearthquake rupture processtrapped wavedownhole seismic observationSubduction zone drilling into a seismogenic zone has recently been planned to understand the mechanics of large thrust earthquakes. We review studies on fault zone structures in land areas and fault mechanics studies related to the fault zones. We also point out possibilities of estimating the parameters of slip-weakening and/or rate and state dependent friction laws from a parameter of thickness of fault gouges or of fault damaged zones observed in the borehole. Two types of low velocity zone, the fault and the oceanic crust low-velocity zones (FLVZ and CLVZ), can be expected along the subduction zone plate-boundary. Delineations of FLVZ and CLVZ clarify the frictional properties of the sunduction zone plate-boundary and detailed structures of the subducting oceanic crust at deeper parts. The trapped wave observation in the subduction zone borehole is a useful tool for delineating FLVZ and CLVZ in the upper parts of the subducting slab

Low-velocity zones along subducting oceanic plates : Their implications in the subduction-zone seimogenesis and a method to detect them

low-velocity zonesubduction zoneearthquake rupture processtrapped wavedownhole seismic observationSubduction zone drilling into a seismogenic zone has recently been planned to understand the mechanics of large thrust earthquakes. We review studies on fault zone structures in land areas and fault mechanics studies related to the fault zones. We also point out possibilities of estimating the parameters of slip-weakening and/or rate and state dependent friction laws from a parameter of thickness of fault gouges or of fault damaged zones observed in the borehole. Two types of low velocity zone, the fault and the oceanic crust low-velocity zones (FLVZ and CLVZ), can be expected along the subduction zone plate-boundary. Delineations of FLVZ and CLVZ clarify the frictional properties of the sunduction zone plate-boundary and detailed structures of the subducting oceanic crust at deeper parts. The trapped wave observation in the subduction zone borehole is a useful tool for delineating FLVZ and CLVZ in the upper parts of the subducting slab