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Published October 18, 2010 | public
Journal Article

Supershear transition due to a free surface in 3-D simulations of spontaneous dynamic rupture on vertical strike-slip faults

Abstract

Supershear rupture propagation has been inferred from seismic observations for natural faults and observed in laboratory experiments. We study the effect of the free surface on the transition of earthquake rupture from subshear to supershear speeds using simulations of spontaneous dynamic rupture on vertical strike-slip faults. We find that locally supershear rupture near the free surface can occur due to (i) the generalized Burridge–Andrews mechanism, that is, a supershear loading field between P- and SV-wave arrivals generated by the main rupture front at depths, and (ii) the phase conversion of SV to P-diffracted waves at the free surface. Weaker supershear slip due to the generalized Burridge–Andrews mechanism is caused by the low strength at shallow portions of the fault relative to deeper ones. Dominant supershear rupture is supported by the additional supershear loading field produced by phase conversion. Locally supershear propagation at the free surface occurs regardless of the level of prestress and can cause transition to supershear propagation over the entire seismogenic depth. Such global supershear transition, which depends on prestress, can occur under prestress levels lower than the theoretical estimates for models with no free surface. Although the effectiveness of supershear transition due to the free surface can be diminished by several potentially important factors, it may play an important role on natural faults, at least in those strike-slip earthquakes that accumulate significant surface slip.

Additional Information

© 2010 Elsevier B.V. Received 12 November 2009; revised 1 June 2010; accepted 21 June 2010. Available online 1 July 2010. This study was supported by the National Science Foundation (grant EAR0548277) and the Southern California Earthquake Center (SCEC). SCEC is funded by NSF Cooperative Agreement EAR-0106924 and USGS Cooperative Agreement 02HQAG0008. The SCEC contribution number for this paper is 1324. The numerical simulations for this research were performed on Caltech Division of Geological and Planetary Sciences Dell cluster. We thank Don Helmberger, Daoyuan Sun, and Steve Day for helpful discussions.

Additional details

Created:
August 22, 2023
Modified:
October 21, 2023