Numerical study of splay faults in subduction zones: The effects of bimaterial interface and free surface

Abstract

[1] Splay faults are a characteristic branching fault system in some subduction zones. We model a megathrust earthquake rupture with a branching fault, inhomogeneous media, and a free surface, using a spontaneously propagating mode II crack on a bimaterial interface. For this purpose, we develop an explicit finite element code to solve the elastodynamic equations and a slip-weakening friction law on the fault plane. In a homogeneous prestress condition, the rupture on the branching fault is enhanced when the upper medium is more compliant. Even when the upper medium is less compliant, a fast rupture propagating at a velocity close to the generalized Rayleigh velocity produces the strong dynamic stress around the rupture front and activates the branching fault. When prestress linearly increases with depth from zero at the free surface, only a slight change of normal stress that is due to seismic waves causes an initiation of rupture on the branching fault at the free surface, and this rupture propagates downward on the branching fault. The arrival of this descending rupture at the branching point greatly changes the stress field in the surrounding area. It affects the slip distribution on the main fault and even terminates the main rupture propagation if it occurs before the arrival of the main rupture on the branching point.Citation: Tamura, S., and S. Ide (2011), Numerical study of splay faults in subduction zones: The effects of bimaterial interface and free surface,

Unexpected coseismic surface uplift at Tirúa-Mocha Island area of south Chile before and during the Mw 8.8 Maule 2010 earthquake: a possible upper plate splay fault

“…That fault propagated upward at 45° with west vergence. This is the same mechanism of development of splay faults in subduction zones and its activity in the subduction seismic cycle indicated by Fukao (1979), Cummins et al (2001, Wendt et al (2009), Tamura and Ide (2011), De Dontney and Hubbard (2012), and Li et al (2014. The tip point of Tirúa-Mocha splay fault did not reached the sea bottom between Tirúa and Mocha Island during the 1960-2010 interseismic period (Fig.…”

“…Splay faults in subduction zones have been documented from seismic profiles at the Nankai Through of Japan (Moore et al, 2007;Strasser et al, 2009;Gulick et al, 2010), Colombia-Ecuador (Collot et al, 2008), Alaska (Liberty et al, 2013) and Iran-Makran subduction zones (Heidarzadeh, 2011). During subduction earthquakes, splay faults can accommodate part of the coseismic slip (Fukao, 1979;Cummins et al, 2001;Tamura and Ide, 2011;De Dontney and Hubbard, 2012;Li et al, 2014;Wendt et al, 2009). One remarkable case resulted from the Mw=9.2 1964 Alaska earthquake, where the Patton Bay and Hanning Bay reverse faults at Montague Island, generated an additional coseismic uplift which was recorded in the visible pattern of fault scarps (Plafker, 1972).…”

Modeling Megathrust Earthquakes Across Scales: One‐way Coupling From Geodynamics and Seismic Cycles to Dynamic Rupture

“…It has been suggested that these splay faults play an important role during tsunamigenesis, because they could potentially accommodate large vertical displacements (Fukao, ). Therefore, several dynamic rupture studies have investigated fault branching and splay fault activation, mostly using simplified geometries (DeDontney & Rice, ; Li et al., ; Madden et al., ; Tamura & Ide, ; Uphoff et al., ; Wendt et al., ). Choosing appropriate stress and strength for both the megathrust and the splay fault has been shown to crucially affect branching and dynamic triggering (DeDontney & Hubbard, ; DeDontney et al., ).…”

A self‐consistent mechanism for slow dynamic deformation and tsunami generation for earthquakes in the shallow subduction zone

“…Slip on pre‐existing splay faults off the plate interface is also a viable mechanism for large tsunamigenesis [e.g., Fukao , 1979; Moore et al , 2007]. The steeper dip of the splay fault would significantly increase the potential for tsunamigenesis, which has motivated extensive theoretical studies [e.g., Wendt et al , 2009; DeDontney et al , 2011; Tamura and Ide , 2011] to investigate the conditions under which a splay fault can be activated in subduction zones; however, it does not readily explain the lack of high frequency seismic radiation.…”