Earthquake cycles with dynamic weakening from flash melting with heterogeneous stress and near-fault anelastic strain

Norman H. Sleep

Submitted July 17, 2017, SCEC Contribution #7309, 2017 SCEC Annual Meeting Poster #186

Major earthquakes may nucleate at high-shear-traction patches of strike-slip faults left over from heterogeneous slip in past events. Once an earthquake is underway, the slip-weakening distance can be less than 1 mm for rate and state friction and much less for flash melting, which greatly weakens the fault plane. The slip-weakening velocity is ~0.05-0.2 m/s. The rate and state strength of the fault is briefly reached at the rupture tip and then fault may dynamically weaken for most of the slip even in a small event. However, a simple version of this process with the fault becoming suddenly weak generates extreme seismic waves in large events that would cause anelastic failure in the near-fault environment. Near-fault failure occurs within the tip zone. It accommodates macroscopic slip near the rupture tip, increasing the effective slip weakening distance and maintaining shear tractions near the frictional failure criterion. The associated anelastic strain is heterogeneous and produces residual stresses and undulations of the fault plane. Conversely, strong seismic waves in the tip region trigger anelastic deformation that preferentially relaxes residual stresses and stress build up from undulations in the fault plane. A balance is reached statistically maintaining on-fault residual stress and undulations and near-fault residual stresses. A fraction of the frictional energy of the event scaling with the macroscopic stress drop divided by the peak strength produces anelastic deformation in the tip zone, residual stresses, and undulations. Strong high-frequency waves produce sustained oscillating (several Hz) particle velocities comparable to the flash-weakening velocity. Fault patches that are about to cease slipping do so in an irregular fashion, augmenting the irregularities formed at the rupture tip.

Key Words
Dynamic rupture, heterogeneous fault slip, fractals

Citation
Sleep, N. H. (2017, 07). Earthquake cycles with dynamic weakening from flash melting with heterogeneous stress and near-fault anelastic strain. Poster Presentation at 2017 SCEC Annual Meeting.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)