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Dynamic Slip Transfer from the Denali to Totschunda Faults, Alaska: Testing Theory for Fault Branching

¹ Harvard University
Division of Engineering and Applied Sciences
29 Oxford Street
Cambridge, Massachusetts 02138
bhat{at}esag.harvard.edu
 (H.S.B.)

² Harvard University
Division of Engineering and Applied Sciences and
Department of Earth and Planetary Sciences
29 Oxford Street
Cambridge, Massachusetts 02138
 (R.D.)

³ Harvard University
Division of Engineering and Applied Sciences and
Department of Earth and Planetary Sciences
29 Oxford Street
Cambridge, Massachusetts 02138
 (J.R.R.)

⁴ Kyushu University
Department of Earth and Planetary Sciences
Faculty of Sciences
6-10-1 Hakozaki
Higashi-ku
Fukuoka 812-8581
Japan
 (N.K.)

We analyze the observed dynamic slip transfer from the Denali to Totschunda faults during the M_w 7.9 3 November 2002 Denali fault earthquake, Alaska. This study adopts the theory and methodology of Poliakov et al. (2002) and Kame et al. (2003), in which it was shown that the propensity of the rupture path to follow a fault branch is determined by the preexisting stress state, branch angle, and incoming rupture velocity at the branch location. Here we check that theory on the Denali-Totschunda rupture process using 2D numerical simulations of processes in the vicinity of the branch junction. The maximum compression direction with respect to the strike of the Denali fault near the junction has been estimated to range from approximately 73° to 80°. We use the values of 70° and 80° in our numerical simulations. The rupture velocity at branching is not well constrained but has been estimated to average about 0.8 c_s throughout the event. We use 0.6 c_s , 0.8 c_s , 0.9 c_s , and even 1.4 c_s as parameters in our simulations. We simulate slip transfer by a 2D elastodynamic boundary integral equation model of mode II slip-weakening rupture with self-chosen path along the branched fault system. All our simulations except for 70° and 0.9 c_s predict that the rupture path branches off along the Totschunda fault without continuation along the Denali fault. In that exceptional case there is also continuation of rupture along the Denali fault at a speed slower than that along the Totschunda fault and with smaller slip.