Spectral-element modeling of spontaneous earthquake rupture on rate and state faults: Effect of velocity-strengthening friction at shallow depths

Kaneko, Yoshihiro and Lapusta, Nadia and Ampuero, Jean-Paul (2007) Spectral-element modeling of spontaneous earthquake rupture on rate and state faults: Effect of velocity-strengthening friction at shallow depths. Journal of Geophysical Research - Solid Earth.

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Abstract

We develop a spectral-element methodology (SEM) for simulating dynamic rupture on rate and state faults and use it to study how the rupture is affected by a shallow fault region of steady-state velocity-strengthening friction. Our comparison of the developed SEM and a spectral boundary-integral method (BIM) for an anti-plane (two-dimensional) test problem shows that the two methods produce virtually identical solutions for the finest resolution we use and that the convergence with grid reduction of the developed SEM methodology is comparable to that of BIM. We also use the test problem to compare numerical resolution required for different state evolution laws and for linear slip-weakening friction. Using our three-dimensional implementation of the methodology, we find that a shallow velocity-strengthening fault region can significantly alter dynamic rupture and ground motion. The velocity-strengthening region suppresses supershear propagation at the free surface occurring in the absence of such region, which could explain the lack of universally observed supershear rupture near the free surface. In addition, the velocity-strengthening region promotes faster fall-off of slip velocity behind the rupture front and decreases final slip throughout the entire fault, causing a smaller average stress drop. The slip decrease is largest in the shallow parts of the fault, resulting in the depth profile of slip qualitatively consistent with observations of shallow co-seismic slip deficit. The shallow velocity-strengthening region also reduces the amplification of strong ground motion due to a low-velocity bulk structure.

EPrint Type:	Article
Additional Information:	Nadia Lapusta gratefully acknowledges the support of the National Science Foundation (Grant EAR 0548277) and the Southern California Earthquake Center. SCEC is funded by NSF Cooperative Agreement EAR-0106924 and USGS Cooperative Agreement 02HQAG0008. The SCEC contribution number for this paper is xxxx. Jean-Paul Ampuero is supported by SPICE, a Marie Curie Research and Training Network in the 6th Framework Program of the European Commission. This is ETH contribution xxxx. The numerical simulations for this research were performed on Caltech Division of Geological and Planetary Sciences Dell cluster. We thank Tom Heaton, Qinya Liu, and Yi Liu for helpful discussions.
Uncontrolled Keywords:	earthquake rupture dynamics, rate and state friction, spectral-element methods
ID Code:	18
Deposited By:	Mr Yoshihiro Kaneko
Deposited On:	30 January 2008
Record Number:	CaltechSOLIDS:2008.001
Official Persistent URL:	http://resolver.caltech.edu/CaltechSOLIDS:2008.001
Official Citation:	Y. Kaneko, N. Lapusta, and J.-P. Ampuero (2008) Spectral-element modeling of spontaneous earthquake rupture on rate and state faults: Effect of velocity-strengthening friction at shallow depths. Caltech Solids Report 2008-001, 17 December 2007. http://resolver.caltech.edu/CaltechSOLIDS:2008.001
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