Dip angles of active faults from the surface to the seismogenic zone inferred from a 2D numerical analysis of visco-elasto-plastic models: a case study for the Osaka Plain

Abstract The geometries (i.e., dip angles) of active faults from the surface to seismogenic zone are most important factors used evaluate earthquake ground motion, which is crucial for seismic hazard assessments in urban areas. In Osaka, a metropolitan city Japan, there several (e.g., Uemachi and Ikoma faults), inferred topography, attitude trenches, reflection profile at shallow depths (less than 2 km), three-dimensional distribution Quaternary sedimentary layers. N–S-striking fault systems with total lengths 42 km 38 km, respectively, former being located ~ 12 west latter; however, each within not clear. this study, examine zone, we analyze development geological structures layers based on numerical simulations two-dimensional visco-elasto-plastic body under horizontal compressive stress field, including preexisting high-strained weak zones faults) sedimentation processes, relationship between observed sediments Osaka Group) Plain model results. As result, propose zone. When friction coefficient 0.5, angles near 30°–40° has downward convex curve bottom but does converge fault. Based analysis angle estimated be approximately 30°–40°, lower that previous studies. If low angle, width plane long, thus moment will large.