STATIC COULOMB STRESS ANALYSIS FOR EARTHQUAKES IN THE SPREADING RIDGE OF THE SOUTH CHINA SEA

Based on the distribution pattern of earthquakes and the maximum principal stress direction along the Manila Trench and its adjacent region, combined with the static Coulomb stress analysis for the paleo-ridge segment of the Manila subduction zone, we found the zonal distribution of earthquakes in the northern area of Manila Trench. The maximum principal stresses are dominated by the stress in northwest direction. However, the compressive stress is mainly in eastwest direction in the paleo-ridge segment of the Manila subduction zone. The earthquake with the moment magnitude of 7.2 happened on December 11, 1999 brought about the subsequent 2000 M_w6.2 earthquake and 2011 M_w6.0 earthquake, with an increase of the static Coulomb stresses upto 0.5 bar and 0.3 bar respectively which are closer to the Coulomb failure. The static Coulomb stress change of the earthquake with the moment magnitude 6.0 and the aftershock in a moment magnitude of 5.0 on November 30, 2011,which was caused by normal faults, can better reflect the corresponding relationship of the aftershock distribution. Most of aftershocks are located in the areas with Coulomb stress increased greater than 0.1 bar. The calculation result of the Coulomb stress change of the normal receiver faults imparted from ridge segment shows that the Coulomb stress increased 0.3~0.5 bar in less than 10 km depth ranges and they are mainly along the NE distribution on the ridge segment side. The Coulomb stress increased in an area as deep as 20 km on the Luzon arc side, and is consistent with the earthquakes distribution.