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

Abstract

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 , 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 DenaliTotschunda 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 73Њ to 80Њ. We use the values of 70Њ and 80Њ 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 70Њ 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.

Off‐fault plasticity and earthquake rupture dynamics: 1. Dry materials or neglect of fluid pressure changes

“…[16] Along a portion of the fault of length L 0 c , we impose an initial shear stress distribution consistent with a slipweakening shear crack in energetic equilibrium like in the work by Kame et al [2003] and Bhat et al [2004] to nucleate a dynamic shear rupture. The length of the nucleation zone, L 0 c , is chosen somewhat greater than the critical nucleation length at instability, calculated by Palmer and Rice [1973] and given here for n = 0.25 as…”

Finite Element Modeling of Branched Ruptures Including Off-Fault Plasticity

“…Bhat et al (2004) studied the 2002 Denali event, Fukuyama and Mikumo (2006) studied the 1891 Nobi event, and Oglesby et al (2003) examined the 1999 Hector Mine event. The surface rupture of the 1992 Landers earthquake activated multiple fault branches and illustrates the complexities of a rupture path (Sowers et al, 1994).…”

“…The dynamics of earthquake rupture through branched geometries has been studied (e.g., Aochi et al, 2000;Kame et al, 2003;Bhat et al, 2004;Duan and Oglesby, 2007), but the physical processes that take place at the branching junction have not been thoroughly examined. The presence of the triple junction introduces physical and algorithmic complexities that require attention.…”

Dynamic Rupture through a Branched Fault Configuration at Yucca Mountain, and Resulting Ground Motions

“…The criteria for dynamic branch activation in natural fault systems have been extensively studied (Poliakov et al, 2002;Kame et al, 2003;Oglesby et al, 2003;Bhat et al, 2004;Oglesby et al, 2004, Bhat et al, 2007Duan and Oglesby, 2007). Poliakov et al (2002) identified locations of possible branch activation by investigating the dynamic stress field surrounding a rapidly propagating semi-infinite nonsingular mode II distance-weakening shear rupture in an elastic material.…”

“…They suggested that the prestress state and rupture velocity control the location of zones where the crack-tip stress field could violate a Mohr-Coulomb (MC) failure criterion and potentially nucleate rupture along a preexisting branch. Kame et al (2003), Bhat et al (2004), and Fliss et al (2005) extended the work of Poliakov et al (2002) by including preexisting branch faults to investigate, in the framework of slip-weakening modeling of spontaneous rupture, how rupture velocity, prestress state, and *Now at ExxonMobil Upstream Research Company, Houston, Texas. angle of the preexisiting branch control dynamic branch activation. Those studies focused on explaining branch activation during recent large earthquakes such as the 1992 Landers earthquake (Fliss et al, 2005), the 2002 Denali earthquake (Bhat et al, 2004), the 1971 San Fernando, the 1985 Kettleman Hills, and the 1979 Imperial Valley earthquakes (Kame et al, 2003).…”