Numerical modeling of stress change related to fault activities in an accretionary wedge

We modeled formation process of an accretionary wedge by using numerical simulation, and calculated stress distribution in the modeled accretionary wedge. The simulation results show us dynamic stress change during the formation process of the wedge. The formation process of the wedge is divided into four stages; sedimentation stage, pre-frontal thrust stage, frontal thrust stage and post-frontal thrust stage. In the first stage, the sediments accumulate far from a trench. In the second stage, the sediments gradually approach to the trench with an oceanic plate subduction. In the third stage, the sediments are accreted to the wedge and a frontal thrust is formed in the sediments. The new frontal thrust is the most active fault in the frontal part of the wedge. In the last stage, the activity of the frontal thrust rapidly decreases after the generation of a younger frontal thrust. Stress patterns in the wedge change in each stage. The direction of the maximum compressive stress (MCS) is vertical in the sedimentation stage. In the pre-frontal thrust stage, the magnitude of MCS increases and the inclination of MCS rotates to horizontal. The inclination of MCS then rotates to normal to the frontal thrust surface while this surface is moving. In the post-frontal thrust stage, the direction of MCS again changes to horizontal. These results suggest that these differences in the stress patterns are related to the wedge deformation. Especially fault activity changes the stress pattern dramatically. Our analysis suggests that the horizontal component of the stress decreases along the fault while the fault is active, and this decrease makes the rotation of MCS. We are now continuing the analysis to reveal the relation between stress and deformation in the wedge and can be shown at the meeting.