Title: Integrating observations with numerical models to understand complexities in earthquake dynamics
Speaker: Dr. Dunyu Liu
Postdoctoral Research Associate, Texas A&M University
Abstract: Physics-based numerical models, powered by rapidly advancing computing power and parallel computing, allow simulations of earthquake dynamics over wide ranges of spatial and temporal scales. Such models show potentials to synthesize physics and observations from various disciplines and lead to a multidisciplinary understanding of complex earthquake dynamics. Three studies will be presented. In the first study, subhorizontal fractures in fault damage zones are observed exclusively at the bend of the North Branch of the San Gabriel fault in southern California. We simulate dynamic ruptures on a strike-slip fault with a bend in an elastoplastic medium and find that initial stress orientations and magnitudes, rupture directions, and the free surface are critical factors in yielding off-fault subhorizontal fractures. The fact that subhorizontal fractures tend to concentrate on the north side of the bend may indicate a preferred rupture direction in the fault system. By extending the temporal horizon of earthquake processes into the past few thousands of years, paleoseismological data show that earthquakes on the southern San Andreas and San Jacinto faults had irregular rupture extents and recurrence intervals at a specific site. In the second study, we simulate mutlicycle dynamics of the southern San Andreas and San Jacinto faults with realistic fault geometry as a key factor. With loading conditions from geodesy, the models can reproduce the complexities in observations from paleoseismology, geology, and seismology. The models demonstrate the critical roles of fault geometry and dynamic ruptures in earthquake behaviors on the fault system. The next big earthquake on the southern San Andreas and San Jacinto faults could either nucleate north of the big bend or near Cajon Pass, posing different ground shaking hazards to the nearby communities. To fully resolve all the deformation phases over earthquake cycles in 3D is computationally challenging, especially for geometrically complex fault systems. In the third study, a parallel finite element earthquake simulator is developed to simulate fully dynamic earthquake cycles governed by experimentally derived rate- and state- dependent friction on geometrically complex fault systems. Models show that even a single bend will yield complex rupture patterns over multiple earthquakes cycles.