PARAMETRIC STUDY ON GROUND SURFACE DEFORMATION FORMING PULL-APART STRUCTURE CAUSED BY FAULT MOVEMENT

Abstract

 The prediction of surface ruptures during an earthquake is important to consider the hazard assessment on the social infrastructure. Two strike-slip faults sometimes produce a pull-apart structure in the region sandwiched by the faults, resulting in a subsidence field. Although there are individual case reports on pull-apart structures, the fundamental mechanism and features of the pull-apart structure are still unclear. Using the finite element method, I thus conducted a parametric study (715 cases in total) by changing tectonic stress setting, step-over distance, and overlap of faults to reveal the relationship between the above parameters and the magnitude of subsidence in the pull-apart structure. The notable results are: (1) An extremely large overlap cannot produce intense subsidence irrespective of the magnitude of step-over, (2) The direction of principal stress affects the magnitude of the subsidence, but it does not affect the displacement pattern of the ground surface, (3) The sensitivity of overlap to the subsidence is larger than that of the step-over to the subsidence, and (4) The NSGA-II optimization algorithm successfully detects each tectonic setting: one for subsidence maximization and the other for the strike components maximization.