[1poster01-13] T10 ［Topic Session］Deformation and reaction of rocks and minerals

ECS

[T10-P-1] Multi-stage high-velocity slip experiments to elucidate frictional evolution and earthquake energetics in gabbroic faults

*Dyuti Prakash Sarkar¹, Takehiro Hirose¹, Wataru Tanikawa¹, Yohei Hamda¹, Hanaya Okuda¹ (1. Japan Agency for Marine Earth Science and Technology)

Keywords:

friction,fault,slip pulse,frictional melting,breakdown energy

Earthquake along fault planes is attributed to shear rupture instabilities that usually activate damage in the fault core and surrounding damage zone. Such seismogenic faults usually exhibits several earthquake events during their lifetime. Each earthquake events augments to the heterogeneity of structure and strength of the fault zones, leading to changes in the mechanical properties and energy conditions of subsequent events. However, the evolution of the mechanical properties and energy conditions associated with multiple earthquake events is not well understood. In present study, a series of high-velocity slip-pulse experiments were conducted on simulated gabbro faults to investigate the evolution of mechanical properties of faults undergoing multiple slip events.The experiments are conducted in dry conditions with a pair of hollow cylinders of Belfast gabbro specimens that are repeatedly sheared using the Pressurized High Velocity (PHV) apparatus at slip velocity of 1 m/s and normal stresses of ~ 4 MPa. Each slip pulse representing a single earthquake event results in a total displacement of ~3.8 m. In the present study, we have attempted up to 5 slip pulses for each experiment. During the experiments, the frictional heating inevitably occurs leading to melting and temperatures ~1100–1300 ℃ at the simulated fault contact. Two stages of slip weakening are observed with one following the initial slip, and the other weakening occurs just after the second peak friction. The first weakening is associated with the flash heating at the asperity contacts, while the second weakening is attributed to formation and growth of the melt layer along the simulated fault. The two-stage slip weakening can be confirmed for all the slip pulses, however the displacement required for slip weakening decreases with subsequent slip pulses. This suggests that energy requirement decreases to initiate slip weakening associated with frictional melting in subsequent slip events. We will discuss the microstructural characteristics of the recovered samples observed by X-Radia micro-CT and SEM of the thinsections to clarify the mechanochemical processes in the fault zones. Our results elucidate the evolution of mechanical properties and breakdown energy in repeated earthquake sequences.