Dynamic Rupture Modeling of the Transition from Thrust to Strike-Slip Motion in the 2002 Denali Fault Earthquake, Alaska

Abstract

We use three-dimensional dynamic (spontaneous) rupture models to investigate the nearly simultaneous ruptures of the Susitna Glacier thrust fault and the Denali strike-slip fault. With the 1957 M w 8.3 Gobi-Altay, Mongolia, earthquake as the only other well-documented case of significant, nearly simultaneous rupture of both thrust and strike-slip faults, this feature of the 2002 Denali fault earthquake provides a unique opportunity to investigate the mechanisms responsible for development of these large, complex events. We find that the geometry of the faults and the orientation of the regional stress field caused slip on the Susitna Glacier fault to load the Denali fault. Several different stress orientations with oblique right-lateral motion on the Susitna Glacier fault replicate the triggering of rupture on the Denali fault about 10 sec after the rupture nucleates on the Susitna Glacier fault. However, generating slip directions compatible with measured surface offsets and kinematic source inversions requires perturbing the stress orientation from that determined with focal mechanisms of regional events. Adjusting the vertical component of the principal stress tensor for the regional stress field so that it is more consistent with a mixture of strike-slip and reverse faulting significantly improves the fit of the sliprake angles to the data. Rotating the maximum horizontal compressive stress direction westward appears to improve the fit even further.

Dynamic rupture of the 2011 Mw 9.0 Tohoku‐Oki earthquake: Roles of a possible subducting seamount

“…Further studies using spontaneous rupture models are needed to gain physical insights into dynamic rupture propagation, seismic radiations, and ground motion excitation. 3D spontaneous rupture modeling studies have been conducted for some of recent large earthquakes, such as the 1992 Landers [e.g., Olsen et al , 1997; Aochi and Fukuyama , 2002], the 1999 Hector Mine [e.g., Oglesby et al , 2003], the 1999 Izmit, Turkey [e.g., Harris et al , 2002], the 1999 Chi‐Chi [e.g., Oglesby and Day , 2001], the 2002 Denali fault, Alaska [e.g., Aagaard et al , 2004; Oglesby et al , 2004], and the 2008 Wenchuan, China [e.g., Duan , 2010b] earthquakes. These studies have gained physical insights into some rupture and/or ground motion characteristics of these earthquakes.…”

Constraining fault constitutive behavior with slip and stress heterogeneity

“…On the other hand, if V 0 > 0, then restrengthening occurs while the slip rate is greater than zero producing rate‐activated restrengthening where r controls the rate of restrengthening. This formulation is slightly more stable numerically than a direct rate dependence (used in previous studies such as those by Aagaard et al [2001] Anderson et al [2003], and Aagaard et al [2004]) because the rate of restrengthening is constant and does not increase as the slip rate decreases.…”

“…We normalize stress related fault constitutive model parameters with respect to the shear modulus, which gives rise to behavior that is similar to using a homogeneous half‐space. We use the same spontaneous dynamic rupture finite element code as we have used in previous studies [e.g., Aagaard et al , 2001, 2004]; in benchmark tests [ Harris and Archuleta , 2004] it gives very similar results to several other finite element and finite difference spontaneous rupture codes. We discretize the domain using linear tetrahedral finite elements with the length of element edges set to approximately one tenth of the wavelength of shear waves with periods of 1.0 s. The elements at the bottom of the domain have 375 m long edges whereas the elements at the top of the domain have 265 m long edges (very similar results were obtained for simulations with elements twice these sizes).…”

Dynamic transfer of rupture across differently oriented segments in a complex 3‐D fault system

“…As numerically demonstrated for the 2002 Denali, Alaska, earthquake [e.g., Dreger et al , 2004; Aagaard et al , 2004], fault rupture can be quite complex, beginning on dipping fault segments and continuing along vertical strike‐slip segments. The purpose of this paper is to explore with a simple dynamic modeling scheme, whether such complexity can be expected in most cases where complex faulting systems exist, or on the contrary, such complex rupture behavior is restricted to specific conditions.…”