Rupture Propagation and Arrest in Geometrically Complex Fault Systems: Bends, Stepovers, and Damaged Border Zones

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Abstract for proposal EAR-0105344 (PH # 37x)Title: Rupture propagation and arrest in geometrically complex fault systems: Bends, stepovers, and damaged border zonesPI's: James R. Rice (principal investigator) and Renata Dmowska (senior co-investigator), Dept. of Earth and Planetary Sci. and Div. of Engin. and Appl. Sci., Harvard Univ.Our project seeks to understand mechanical principles controlling earthquake rupture propagation and arrest in geometrically complex fault systems. As part of that we are devising numerical methodology to model dynamic rupture with inclusion of non-planarity of fault surfaces, step-overs and branches in fault networks, activation of smaller faults or fractures in the region bordering a main fault zone, and simultaneous activation of competitive rupture paths. In general the rupture path cannot be specified a priori but, rather, must be dynamically self-chosen among available fault segments of the network. Geological, geodetic and seismological observations are used to constrain and test developing ideas on how rupture geometry and prevailing stress state, including principal stress orientations, control whether a rupture starts along a branching fault structure, whether it continues for long distances along the branch, how intermittent is the rupture propagation, etc. Those observational cases include thrust (San Fernando 1971, Kettleman Hills 1985) and strike slip (Imperial Valley 1979, Landers 1992, Hector Mine 1999) events in which branching and/or activation of off-fault activity seem to be involved. Other examples are under study throughout the world for major fault systems, including the North Anatolian system, the Izmit 1999 sequence along it, and its possible future continuation near Istanbul.The studies include consideration of how energy is dissipated in dynamic rupture, and what are characteristics of the enriched high frequency seismic radiation.