Microfracture processes in the breakdown zone during dynamic shear rupture inferred from laboratory observation of near-fault high-frequency strong motion |
| |
| Authors: | Naoyuki Kato Kiyohiko Yamamoto Tomowo Hirasawa |
| |
| Institution: | (1) Faculty of Science, Tohoku University, Aoba-ku, 980 Sendai, Japan |
| |
| Abstract: | High-frequency velocities are measured during stick-slip motion in the immediate vicinity of a fault in a granite sample to reveal the microscopic process taking place in the breakdown zone defined in the slip-weakening model. It is found that 1) the onset time of the observed strong motion approximately coincides with the local rupture onset time, 2) the observed near-fault high-frequency strong-motion duration is approximately proportional to the local breakdown time, and 3) the power spectra of strong motions exhibit significant amplitudes at frequencies above the value off
max, wheref
max is a cut-off frequency relevant to rupturing the breakdown zone. These observations suggest that the high-frequency motion would be due to the incoherent brittle microfracture whose characteristic scale is much shorter than the breakdown zone size. We present a stochastic fault model to synthesize the near-fault high-frequency velocity waveforms. In the model, a number of small circular subfaults are distributed randomly on the fault and the rupture onset time of an individual subfault is assumed to be random. The main features of the observed velocity waveforms are well explained by this numerical modeling. It is concluded that approximately half of the total energy of high-frequency elastic waves observed at a point is radiated from the propagating breakdown zone. We emphasize the importance of the observation of near-fault high-frequency strong motions for large shallow earthquakes. |
| |
| Keywords: | Strong-motion duration f
max slip-weakening model asperity brittle fracture |
| 本文献已被 SpringerLink 等数据库收录！ |
