HR: 0800h
AN: T21B-0590    [Abstracts]
TI: Study On Aftershock Triggering In Consideration Of Tectonic Stress Field
AU: * Hu, C
EM: corehu@gmail.com
AF: Department of Geophysics, School of Earth and Space Sciences, Peking University, Beijing, 100871, China
AU: Cai, Y
EM: yongen@pku.edu.cn
AF: Department of Geophysics, School of Earth and Space Sciences, Peking University, Beijing, 100871, China
AB: Abstract: The occurrence of earthquake is related to the strength of rock and tectonic stress field. The seismic risk factor (SRF),D=\left|{τ_n }\right|/(μσ_n ) is proposed to describe the dangerous status of aftershock triggering in this paper. D<1 in a region means no aftershocks to be triggered there, D≥ 1, dangerous and aftershocks probably occur. A main-shock is considered as an unstable dynamic process of stress release induced by fault softening suddenly in mechanics. It may be simulated by reducing the material parameters of the fault which is loaded by the tectonic stress field. The fault of the main-shock is received as a fault zone and the material in it is supposed to be transversely isotropic. The main-shock is simulated by decreasing the shear modulus in the fault zone. The magnitudes and directions of regional tectonic stress filed far away from the epicenter area of the main-shock may be supposed as constant, its directions can be estimated by jointly considering the average directions of P and T axes based on the focal mechanism solution of earthquakes, velocity field from GPS as well as geological survey. As one order of approximation, the magnitudes of the regional tectonic stress field can be estimated by the Coulomb failure criterion. Finite element method (FEM) and the concept of the factor D are used to study the aftershock triggering of the 1976 Tangshan Ms=7.8 earthquake. The results show that: (1) Most of the aftershocks triggered by the Tangshan earthquake occurred in the two-leaf-shaped regions of D≥ 1 near the north-east end of the main-shock fault. The largest leaf is about 100km long and 40km wide. (2) The areas of aftershock triggering predicted by the seismic risk factorD and Δ CFS (the changes in the Coulomb failure stress) are almost the same near the fault. The difference between them is that the aftershock area predicted by Δ CFS≥ 0 is too large and the area predicted by the factor D≥ 1 is limited. The areas of aftershock triggering predicted by Δ CFS≥ 0.04 MPa are nearly the same as those of D≥ 1 obtained by the study. (3) Sometimes Δ CFS =0.01MPa is taken as a low threshold of aftershock triggering. However, Δ CFS≥ 0 only means the probability increase of the earthquake triggering, not means the earthquake will occur. The earthquake occurrence is not only related to Δ CFS, but also to the tectonic stress field before the main-shock.
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: 2007 Fall Meeting