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Dynamic Breakdown Processes and the Generating Mechanism for High-Frequency Elastic Radiation During Stick-Slip Instabilities

2011; American Geophysical Union; Linguagem: Inglês

10.1029/gm037p0013

2328-8779

Mitiyasu Ohnaka, Yasuto Kuwahara, Kiyohiko Yamamoto, Tomowo Hirasawa,

Earthquake Detection and Analysis

Local breakdown processes during stick-slip unstable shear failure have been examined to clarify the physical mechanism for generating high-frequency elastic radiation. Stick-slip was generated along a 40 cm long precut fault in Tsukuba granite samples using a servocontrolled biaxial loading apparatus. The displacement-time function or the slip velocity-time function depends upon an applied normal stress. The frequency content of the elastic waves depends on normal stress; higher-frequency components are generated during stick-slip failure at higher normal stress. A physical explanation for this is given in terms of asperities where sliding surfaces make contact. The cutoff frequency fc originating from slip instability along the fault is related to v/ (v rupture velocity, average distance between two adjacent asperities), and fc can be estimated from the slip velocity power spectra. Interrelations between shear stress τ, displacement and slip velocity V near a tip of the propagating slip zone were investigated to reveal dynamic breakdown processes, during which the strength can degrade regardless of V. Slip failure instability is promoted during the phase dτ/dt 0, and stability during the phase dV/dt<0 regardless of dτ/dt. At a high normal stress, a number of cycles of accelerating and decelerating phases are repeated during a slip failure, showing that the breakdown of local asperities on the slipping surfaces occurs successively during the slip failure.