Fluidization and melting of fault gouge during seismic slip: Identification in the Nojima fault zone and implications for focal earthquake mechanisms

摘要: [1] The record of physical processes that occur during seismic slip events is well preserved in fault rocks from the active Nojima Japan. The formed at about 3 km depth, and comprise thin alternating layers very fine gouge pseudotachylyte derived granite. Each layer thinner than a few millimeters, corresponds to one event. zone width suggests some mechanisms weakening operated, our studies suggest fluidization melting were particularly important. Fluidized nonfluidized gouges distinguished using detection probability fragmented counterparts method. It known granular material science phase transition grain friction regime materials can only by small decrease volume fraction solid grains. Once occurs, frictional resistance decreases abruptly nearly zero even before thermal pressurization reaches its extreme state. When melted, governed viscosity melt which depends mainly on temperature, chemical composition, H2O concentration unmelted For each layer, we estimated temperature various indices, measured We synthesized these data reconstruct change events. high (107–9 Pas) initial due combined effect low (750°–800°C) large Thus inevitably restrained instantaneously. this mechanical barrier overcome, reduces continuously dramatically as increases. At 1000°C, 104Pas eventually 10Pas 1280°C. stress drops almost completely rupturing tends run away.