A major problem in earthquake science is to understand rupture through geometrically complex fault systems with bends, branches and stepovers. Such complexities exert major control over the propagation and arrest of rupture. The understanding when and how ruptures stop, which is often associated with such features, is central to understanding seismic risk. This study continues recent developments of the theory and modeling of fault fracture at encounters with kinks, bends and offsets between fault segments. That is done with close reference to explaining rupture patterns as observed in field examples. Those include branches and stepovers in major strike-slip earthquakes (e.g., 2001 Kunlun, Tibet, 2002 Denali, Alaska, and 1992 Landers, California), and splay thrust faulting like that documented for the 1944 Nankai, Japan, and 1964 Alaska subduction zones, with implications for tsunami generation.
The studies open new frontiers in rupture dynamics and the physics of earthquakes. Those include a basic understanding of how rupture paths are chosen through complex fault systems, and of the formulation of appropriate computational models (based on dynamic finite element and boundary integral equation methodology) to analyze slip propagation through kinks and branches. In such cases there are significant, coupled, dynamic changes in both the normal and shear stress components supported by the fault, which pose new challenges to representing fracture propagation. Progress in correlating theory with field (and sometimes lab) examples is providing new ways of looking at fault geometry and evidence about prestress states, and translating that into predictions about rupture paths. An important issue under study is whether relic fault geometries with branches and other complexities can be used to infer the direction of rupture in past events, which is important for identifying regions of most severe ground motion. Also, the work addresses how damage zones along faults evolve by successive ruptures, and how inelastic processes within such zones may interact back with stress transmission to the rupture front and with the dynamics of propagation to generate high frequency seismic wave emission.
The project during the previous funding cycle was also effective in aiding the participation of women in research. That includes the co-PI, a graduate student research assistant, and three visiting student interns who completed research on fault rupture as capstone projects in completion of their degree programs elsewhere.
