A PRELIMINARY STUDY ON STATIC STRESS TRIGGERING EFFECTS ON MANILA SUBDUCTION ZONE BY THE PHILIPPINE Mw 7.7 EARTHQUAKE 1990

Based on the solutions of earthquake focal mechanism and the half space homogeneous elastic model, we calculated the variation in stress fields after the Mw 7.7 earthquake. Our results show that the two subsequent strong aftershocks were triggered by the Mw 7.7 earthquake of 16 July 1990, and the static Coulomb stress increased by 21.63 bars and 9.15 bars, respectively. Based on the principles of earthquake recurrence and the structural extrapolation, we used the earthquake focal mechanism solutions for the events greater than Mw 6.0 along the Manila Trench and its adjacent region, one of the nodal plane of the focal mechanism was taken as the receive fault plane in the static stress triggering calculation. The results show that the effect of static Coulomb stress on the Manila subduction zone caused by the Mw 7.7 is mainly concentrated in some faults of the West Luzon Trough, but the variation in Coulomb stress is very small, which has little effect on the northern area of the Manila subduction zone.