SCEC Award Number 12207 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Imaging and Modeling Earthquake Rupture Complexity
Investigator(s)
Name Organization
Jean-Paul Ampuero California Institute of Technology
Other Participants One graduate student
SCEC Priorities 3e, 3c, 6b SCEC Groups Seismology, FARM, GMP
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 We narrowed the gap between earthquake simulations and source imaging, to understand earthquake rupture complexity. We enhanced back-projection source imaging by mitigating the “swimming artifact” and developing relative source power estimates. Analyzing the frequency-dependent radiation of the 2011 Tohoku earthquake we developed dynamic rupture models consistent with observations. We imaged the complicated rupture process of the 2012 Mw 8.6 Indian Ocean earthquake, the largest strike-slip earthquake, and investigated implications for dynamic rupture branching, rupture linkage across stepovers, rheology of the deep lithosphere, maximal depth of earthquake rupture and rupture through nominally stable fault regions.

We implemented a strong motion envelope source inversion method and confirmed the deep location of the Tohoku high-frequency radiation. We developed an adjoint source inversion for heterogeneous media, with large number of source parameters and dense station networks, and quantified the resolution of rise time as a function of network density, rupture speed, noise and uncertainties of crustal structure.

We derived relations between rupture speed and peak slip velocity, from fracture mechanics considerations and dynamic rupture simulations with severe velocity-weakening friction and off-fault plasticity. These relations are valid for crack-like and pulse-like ruptures, with sub-shear and super-shear speed, with and without off-fault plasticity, and for 3D dynamic rupture models with heterogeneous initial stress. We quantified, as a function of stress amplitude and orientation, the effect of plasticity on limiting the process zone, rise time, rupture speed, peak slip velocity and distorting the moment tensor. Our results contribute to pseudo-dynamic source modeling for ground motion prediction.
Intellectual Merit Our research attempts to push the boundaries of earthquake source imaging to higher frequencies. This is required to obtain more useful (finer resolution) seismological constraints on earthquake physics. We combine observational studies with insight from dynamic rupture modeling.
This research addresses the following SCEC4 research priorities and requirements:
• 3e: Our results support “dynamic rupture modeling to understand the dynamics of self-healing ruptures, and the potential for repeated slip on the fault during the earthquake.”
• 3c: The tools we developed support “theoretical and numerical modeling of specific fault resistance mechanisms for seismic radiation and rupture propagation”, by assessing the reliability of seismological constraints on such processes.
• 6b: By better constraining the high-frequency aspects of earthquake rupture, our results contribute to “modeling of ruptures that includes realistic dynamic weakening mechanisms and is constrained by source inversions”, and to “produce physically consistent rupture models for broadband ground motion simulation.”
Our proposal directly addresses a priority for FARM in 2012: “propose source-inversion methods with minimal assumptions, and provide robust uncertainty quantification of inferred source parameters”. Our team participates in the TAG Source Inversion Validation.
Broader Impacts The project provided training and research opportunities for four graduate students, one postdoc and one visiting graduate student from Europe. Open source software for 3D kinematic and dynamic rupture was developed, incorporated in the spectral element code SPECFEM3D, distributed and maintained online through the Computational Infrastructure for Geophysics. Software for adjoint source inversion is available upon request. The techniques for source imaging developed in this project have the potential to provide rapid high-frequency source size estimation for the assessment of damage due to large earthquakes, which could contribute to earthquake response and situational awareness. The relations between rupture speed and peak slip velocity developed here can contribute to physics-based approaches for strong ground motion prediction, with potential implications for advanced earthquake engineering practice.
Exemplary Figure Figure 1: Spatiotemporal distribution of high-frequency (HF) radiation of the April 11th 2012 Mw 8.6 Indian Ocean earthquake imaged by back-projection based on the (left) European and (right) Japanese networks. Colored circles and squares indicate the positions of primary and secondary peak HF radiation. Their size is scaled by beamforming amplitude, and their color indicates timing relative to hypocentral time (color scale in center). The secondary peaks of the MUSIC pseudo-spectrum are those at least 50% as large as the main peak in the same frame. The brown shaded circles in the right figure are the HF radiation peaks from the Mw 8.2 aftershock observed from Japan. The colored contours in the Sumatra subduction zone (left) represent the slip model of the 2004 Mw 9.1 Sumatra earthquake. The figure background is colored by the satellite gravity anomaly (left, color scale on bottom left) and the magnetic anomaly (right, color scale on bottom right). Black dots are the epicenters of the first day of aftershocks from the NEIC catalog. The big and small white stars indicate the hypocenter of the mainshock and Mw 8.2 aftershock. The moment tensors of the Mw 8.6 mainshock, Mw 8.2 aftershock, and double CMT solutions of the mainshock are shown as colored pink, yellow, red, and blue beach balls. The red line in the top left inset shows the boundary between the India (IN) and Sundaland (SU) plates. The patterned pink area is the diffuse deformation zone between the India and Australia plate. The red rectangular zone indicates the study area. The top right inset shows the interpreted fault planes (gray dashed lines) and rupture directions (colored arrows). From Meng et al. (2012).
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