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Published September 25, 2012 | Published
Journal Article Open

The transition of dynamic rupture styles in elastic media under velocity-weakening friction

Abstract

Although kinematic earthquake source inversions show dominantly pulse-like subshear rupture behavior, seismological observations, laboratory experiments and theoretical models indicate that earthquakes can operate with different rupture styles: either as pulses or cracks, that propagate at subshear or supershear speeds. The determination of rupture style and speed has important implications for ground motions and may inform about the state of stress and strength of active fault zones. We conduct 2D in-plane dynamic rupture simulations with a spectral element method to investigate the diversity of rupture styles on faults governed by velocity-and-state-dependent friction with dramatic velocity-weakening at high slip rate. Our rupture models are governed by uniform initial stresses, and are artificially initiated. We identify the conditions that lead to different rupture styles by investigating the transitions between decaying, steady state and growing pulses, cracks, sub-shear and super-shear ruptures as a function of background stress, nucleation size and characteristic velocity at the onset of severe weakening. Our models show that small changes of background stress or nucleation size may lead to dramatic changes of rupture style. We characterize the asymptotic properties of steady state and self-similar pulses as a function of background stress. We show that an earthquake may not be restricted to a single rupture style, but that complex rupture patterns may emerge that consist of multiple rupture fronts, possibly involving different styles and back-propagating fronts. We also demonstrate the possibility of a super-shear transition for pulse-like ruptures. Finally, we draw connections between our findings and recent seismological observations.

Additional Information

© 2012 American Geophysical Union. Received 21 May 2012; accepted 5 August 2012; published 25 September 2012. This work was supported by Pacific Gas and Electrics, the National Science Foundation (grant EAR-0944288) and by the Southern California Earthquake Center (which is funded by NSF EAR-0106924 and USGS 02HQAG0008 cooperative agreements). We are grateful to Shiang-Jong Lee for providing his finite source models, and to the Editor, Associate Editor, S.M. Day and anonymous reviewers for their constructive comments. We acknowledge the research computing facilities and support at King Abdullah University of Science (KAUST). This is SCEC contribution number 1654.

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