Coseismic Slip Gradient and Rupture Jumps on Parallel Strike-Slip Faults

Field observations of slip distribution along large strike-slip faults and preliminary rupture model simulations reveal a possible correlation between slip gradient near a fault end and the ability of a rupture to jump over a structure stepover in a strike-slip fault system. We simulate the dynamic rupture process on two parallel strike-slip faults embedded in an elastic medium to investigate this correlation and compare model-generated results with field-measured data. We find that the slip gradients calculated over the final 1 km of a fault have a linear relationship with both the average stress drop on the fault and the largest width of the step that could be jumped by a propagating rupture. Our dynamic coulomb stress analyses show that the average stress drop on the first fault, which is proportional to the slip gradient in the final 1 km, determines the positive coulomb stress region at the end of the first fault, which in turn determines the largest jumpable step width. A larger stress drop results in a larger positive coulomb stress region around the first fault end, which allows the rupture to jump a wider stepover.