Earthquake Dynamics

Raul Madariaga, & Kim B. Olsen

Published 2001, SCEC Contribution #539

The propagation of seismic ruptures along a fault subject to an initial stress distribution and a set of frictional parameters has been studied extensively over the years. When prestress is uniform, rupture propagation is relatively simple with rupture speed in the in-plane direction being faster than that in the antiplane one. Spontaneous rupture fronts are therefore elongated in the in-plane direction. For uniform stress fields, most of the seismic observables (seismic moment, corner frequency, etc) scale with the fault length. Numerical models with a single length scale show that in the initial stages of rupture and near the rupture front stress and velocity fields scale with the slip weakening distance, a characteristic length scale of the friction law. When stress is heterogeneous, as seems to always be the case for earthquakes, rupture propagation is much more complicated. The rupture is then controlled by local length scales determined by the initial stress distribution as well as the local rupture resistance. Thus, the occurrence of phenomena such as rupture pulses with short rise times, rupture arrest, stopping phases,
super-shear rupture velocities and spatial variation of slip are
controlled by the heterogeneous stress field on the fault.
State-of-the-art dynamic rupture models with realistic stress distributions suggest that large earthquakes are typically characterized by a complex rupture path with a spatially strong variation of rupture energy release. Such complex rupture behavior can be modeled numerically by methods such as boundary integral elements and finite differences for historic earthquakes with the friction parameters and stress distributions constrained by
kinematic analyses and strong motion data.

Key Words
1992 landers earthquake, complexity, constitutive relations, fault model, propogation, rate-dependent friction, shear rupture, slip-weakening friction, strain, stress drop,

Madariaga, R., & Olsen, K. B. (2001). Earthquake Dynamics. In Madariaga, R., Olsen, K. B., & (Eds.), International Handbook of Earthquake and Engineering Seismology, (, pp. ) , : IASPEI