An estimation of the absolute stress value for the Landers earthquake source region

We estimate the absolute stress value at the earthquake source region of a small cubic area in Homestead valley fault segment which broke during the Landers earthquake, using seismic stress drop and rotations of stress axes during the event.We obtained the pre-seismic compressive, intermediate and extensional principal stress values as 323, 319 and 312MPa in the depth of 8∼12 km. The shear stresses on the fault plane before and after the event are 6MPa and 1MPa respectively. The results show that normal stress increased after the earthquake, which helps to terminate the rupture process. The pre-seismic shear-stress is greater than that after the quake and their differences roughly correspond to the seismic stress drop. The post-seismic shear-stress is positive, which means no overshooting in co-seismic slip. The differential stress value is less than the absolute stress value, and the shear stress is also relatively small.