Dissertation Defense Announcement

College of Arts and Sciences announces the Final Dissertation Defense of

Khurram Aslam

for the Degree of Doctor of Philosophy

June 18, 2019 at 10:00 AM CERI long building

Advisor: Eric Daub

More is Better: Effect of fault roughness on aftershocks distribution

ABSTRACT: We perform dynamic earthquake rupture simulations of large earthquakes. This modeling resolves the finer scale details of slip based on elasticity and friction and hence has the ability to predict the spatial distribution of slip and stress changes. We perform numerous two dimensional earthquake rupture simulations on rough strike slip faults assuming elastic as well as assuming plastic off-fault material properties. We output the static stress changes in the off-fault medium from our simulations and use these to calculate the Coulomb failure function (CFF) in the region surrounding the fault. We use similar and variable orientations for receiver faults planes to calculate CFF values. The similar receiver fault plane orientations are chosen to be parallel to overall trace of the main fault, while the variable receiver fault orientations are determined using the angle at which plastic shear strain is maximum. Our results show that the stresses are highly complex in the region close to the fault. This complexity reduces as the distance from the fault increases. We conclude that the stress complexity observed in the near-fault region is due to roughness of the fault profile. The complexity of stresses in the near-fault region causes the CFF to be highly heterogeneous in the near-fault region. We observe many positive CFF zones within negative CFF zones in the near-fault region. We believe that these are the potential locations of aftershocks observed in stress shadows. The areas where they appear would be seen as stress shadows in typical static stress change calculations due to insufficient resolution of the fault slip. Furthermore, we observe that the overall trend of the CFF with distance remains similar either assuming elastic or plastic off-fault material properties. Our results suggest that the spatial aftershock distribution surrounding a fault is controlled by both stress heterogeneity as well as the co-seismic damage zone complexity. Comparing our model rupture areas of positive CFF zones with rupture areas of aftershocks and preshocks from relocated earthquake catalogs of Northern and Southern California, we conclude that the stresses in the near-fault region are dominated by the fault roughness effects throughout the seismic cycle.