Off‐fault deformations and shallow slip deficit from dynamic rupture simulations with fault zone plasticity

Kinematic source inversions of major (M≥7) strike‐slip earthquakes show that the slip at depth exceeds surface displacements measured in the field, and it has been suggested that this shallow slip deficit (SSD) is caused by distributed plastic deformation near the surface. We perform dynamic rupture simulations of M 7.2–7.4 earthquakes in elastoplastic media and analyze the sensitivity of SSD and off‐fault deformation (OFD) to rock quality parameters. While linear simulations clearly underpredict observed SSD and OFDs, nonlinear simulations for a moderately fractured fault damage zone predict a SSD of 44–53% and OFDs of 39–48%, consistent with the 30–60% SSD and 46 ± 10% (1σ) OFD reported for the 1992 M 7.3 Landers earthquake. Both SSD and OFDs are sensitive to the quality of the fractured rock mass inside the fault damage zone, and surface rupture is almost entirely suppressed in poor quality material. Key Points We perform dynamic rupture simulations of the 1992 Landers earthquake with inelastic response in the fault damage zone Plastic yielding in fractured fault zones results in a shallow slip deficit of approximately 25‐95% and off‐fault deformations between approximately 20 and 90% Simulated off‐fault deformations obtained for moderately fractured rocks are consistent with values reported from aerial image correlations