Complete Coulomb Failure Stress Changes and Stress Triggering of Yunnan Longling Earthquake Sequence

Abstract

The complete Coulomb failure stress changes caused by the 1976 Ms7.3, Ms7.4 Yunnan Longling double main earthquakes are calculated. And dynamic and static stress triggering effects on the after earthquake sequence are studied. The results show that the second main shock is subjected to the triggering effect of dynamic and static Coulomb stresses induced by the first main shock. Among the thirteen strong aftershocks of the double main shocks, 90% of the aftershocks occurred inside the triangle block are subjected to the triggering effect of dynamic and static Coulomb stresses induced by the first or the second main shock. And 2/3 of the aftershocks occurred outside the triangle block are subjected to the triggering effect of dynamic Coulomb stresses induced by the second main earthquakes. The dynamic and static stress triggering effects of the second main earthquake are stronger than the first main earthquake whether in intensity or in extent. In near field the numbers of triggered aftershocks by dynamic and static Coulomb stress are about equal. However the range of triggering effect of dynamic Coulomb stress is larger than static Coulomb stress.

The Effect on the Nucleation and Failure of MS7.0 Lushan Earthquake Induced by the MS8.0 Wenchuan Earthquake

“…(2) The peak value of dynamic stress change is calculated to be 0.127 MPa on the fault of 2013 Lushan earthquakes, which is much bigger than the value of post-seismic stress change and coseismic static stress change and exceeds the dynamic triggering threshold. Dynamic triggering is induced by the strong transient stress oscillation due to the passage of seismic waves, which may change the steady state and characteristics of the fault (Wu et al, 2007a).…”

“…The method and code PSGRN of Wang et al (2003Wang et al ( , 2006 are used to compute the post-seismic strain field on the basis of fault dislocation and Green function. The dynamic stress change is obtained from theoretical displacement seismogram synthesized with the Discrete Wave-number method (Bouchon, 2003;Wu et al, 2007aWu et al, , 2007b. The source fault is discretized into a two-dimensional array of double-couple points (i.e., cells) distributed on the fault plane, and the displacement field caused by each cell is equal to the displacement field due to the point source of the double couple.…”

“…The dynamic stress change is obtained from theoretical displacement seismogram synthesized with the discrete wave-number method (Bouchon, 2003;Wu et al, 2007a). The source plane is discretized into 10×10 cells; therefore, the whole source plane is equivalent to a combination of 100 double-couple points.…”

“…A fault is not sensitive to a negative dynamic stress pulse, and a positive dynamic stress change has a more obvious influence on the mechanical property of a fault (Kilb et al, 2000). Generally, previous studies use the positive peak value of dynamic stress change to analyze the triggering relationship between the mainshock and following events (Kilb et al, 2000;Antonioli et al, 2002;Wu et al, 2007aWu et al, , 2007b. In this work, we also use the positive peak value of dynamic stress change to analyze the effects of stress changes on failure time caused by dynamic stress change.…”

“…Increasing studies (King et al, 1994;Gomberg et al, 1998;Harris, 2000;Kilb et al, 2002;Wu et al, 2007aWu et al, , 2007b have shown a triggering relationship between major earthquakes and following events in adjacent areas, and the stress changes induced by a major shock may affect the mechanical properties of neighboring faults. However, the change of properties has an uncertain time delay, i.e., there is an uncertain time span between the triggering and triggered earthquakes (Wu et al, 2007a). In some cases, triggered earthquakes happen in hours or days; for example, the Big Bear earthquake occurred only three hours after the Landers earthquake (King et al, 1994).…”