17:15 〜 18:45
[SCG40-P28] Mechanical evolution of gabbro faults during sequence of high-velocity slip pulses with frictional melting
キーワード：断層、摩擦、スリップ・パルス、摩擦溶融
Seismogenic faults experience multiple earthquakes during their lifetimes. Each earthquake event changes the structure and composition of the fault zones, which in turn significantly affects the mechanical properties of the faults in subsequent events. However, the evolution of fault mechanical properties during multiple earthquake sequences is not well understood. We therefore investigate experimentally how the mechanical properties of faults evolve during multiple seismic slip events by performing a series of high-velocity slip-pulse experiments on simulated gabbro faults. Here, we present our preliminary experimental results.
In the experiments, a simulated fault is formed by pressing a pair of hollow cylindrical gabbro specimens. We then repeatedly shear the fault dry at a slip velocity of 1 m/s and normal stress of 3.6 MPa for a total displacement of ~3.8 m during each slip pulse (up to 4 slip pulses). Under these conditions, frictional heating inevitably occurs, leading to frictional melting along the faults (i.e. reproducing the pseudotachylite observed along natural seismogenic faults). The experiments reveal two stages of slip weakening; one following the initial slip and the other immediately after the second peak friction. The first weakening is associated with flash heating at asperity contacts, while the second weakening is due to the formation and growth of a melt layer along the simulated fault. The two-stages of slip weakening behavior is confirmed for all slip pulses. However, the displacement required to initiate the second weakening decreases with slip pulses. In addition, the slip weakening distance during the second weakening also decreases from 1.5 m for the first slip pulse to 0.4 m for the third pulse. This implies that the slip weakening behavior associated with frictional melting is energetically easy to occur in subsequent slip events. Indeed, we confirm that the total frictional energy, defined by the area under the shear stress versus displacement curve, tends to decrease with slip pulses. We plan to perform microstructural analysis to elucidate the underlying mechanochemical processes in the fault zones that control the evolution of mechanical properties with slip pulses. Our results provide new insights into the evolution of fault mechanical properties during multiple earthquake sequences and the implications for the earthquake energy budget during future earthquake events.
In the experiments, a simulated fault is formed by pressing a pair of hollow cylindrical gabbro specimens. We then repeatedly shear the fault dry at a slip velocity of 1 m/s and normal stress of 3.6 MPa for a total displacement of ~3.8 m during each slip pulse (up to 4 slip pulses). Under these conditions, frictional heating inevitably occurs, leading to frictional melting along the faults (i.e. reproducing the pseudotachylite observed along natural seismogenic faults). The experiments reveal two stages of slip weakening; one following the initial slip and the other immediately after the second peak friction. The first weakening is associated with flash heating at asperity contacts, while the second weakening is due to the formation and growth of a melt layer along the simulated fault. The two-stages of slip weakening behavior is confirmed for all slip pulses. However, the displacement required to initiate the second weakening decreases with slip pulses. In addition, the slip weakening distance during the second weakening also decreases from 1.5 m for the first slip pulse to 0.4 m for the third pulse. This implies that the slip weakening behavior associated with frictional melting is energetically easy to occur in subsequent slip events. Indeed, we confirm that the total frictional energy, defined by the area under the shear stress versus displacement curve, tends to decrease with slip pulses. We plan to perform microstructural analysis to elucidate the underlying mechanochemical processes in the fault zones that control the evolution of mechanical properties with slip pulses. Our results provide new insights into the evolution of fault mechanical properties during multiple earthquake sequences and the implications for the earthquake energy budget during future earthquake events.