Journal of Natural Disaster Science

Journal of Natural Disaster Science, Volume 9, Number 1, 1987, pp.1f.

NUCLEATION AND PROPAGATION PROCESSES OF STICK-SLIP FAILURE AND NORMAL STRESS DEPENDENCE OF THE PHYSICAL PARAMETERS OF DYNAMIC SLIP FAILURE

Mitiyasu OHNAKA
Earthquake Research Institute, University of Tokyo
Research Associate, Earthquake Research Institute, University of Tokyo, Tokyo
Yasuto KUWAHARA
Faculty of Science, Tohoku University
and
Kiyohiko YAMAMOTO
Faculty of Science, Tohoku University

(Received 22 December, 1986 and in revised form 1 July, 1987)

Abstract

To understand earthquake failure processes in terms of physics, we have investigated stick-slip shear failure processes using a granite sample with a simulated fault which is large compared with the cohesive zone size. Nucleation preceding dynamically propagating rupture was found for stick-slip failure in a finite localized zone along the fault. In the nucleation zone over which the quasi-static slip motion took place there was no stress increase before the slip-weakening process. No significant difference in the critical displacement was found between the nucleation zone and the zone of dynamic rupture propagation ; however, both breakdown stress drop and shear fracture energy were significantly smaller in the nucleation zone.

The maximum slip velocity and acceleration were much lower in the nucleation zone than in the zone of dynamic rupture propagation. The maximum local slip velocity umax and the maximum slip acceleration amax for dynamic slip failure along the fault increased with increasing normal stress Sn across the fault plane; umax was quadratically related to sn, and amax quartically to sn. The critical displacement uc tended to increase as sn increased. These findings are consistent with an independent observation that the cutoff frequency fmax of the power spectral density of the slip acceleration-time record increases linearly as sn increases. f2max was proportional to amax, and fmax increased with increasing breakdown stress drop, rupture velocity or umax and with decreasing uc.

The maximum slip acceleration during slip failure along the fault is given by

amax=k2umax*umax/uc

in which k2 is a non-dimensional numerical constant, and k2 ‾3 was obtained from the present data set. The cutoff frecquency can be estimated from the relation

fmax={4(1 -n) /p}*(umax/uc)

in which n is Poisson's ratio and p the ratio of the circumference of a circle to its diameter. Size-scale-dependent parameters such as amax are scaled to the cohesive zone size or to the critical displacement, and hence the resilts obtained can be extended to actual earthquake source failure.

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