Cracks, pulses and macroscopic asymmetry of dynamic rupture on a bimaterial interface with velocity-weakening friction

Abstract

SUMMARY We study in‐plane ruptures on a bimaterial fault governed by a velocity‐weakening friction with a regularized normal stress response. Numerical simulations and analytical estimates provide characterization of the ranges of velocity‐weakening scales, nucleation lengths and background stresses for which ruptures behave as cracks or pulses, decaying or sustained, bilateral or unilateral. With strongly velocity‐weakening friction, ruptures occur under a wide range of conditions as large‐scale pulses with a preferred propagation direction, that of slip of the more compliant material. Such ruptures have macroscopic asymmetry manifested by significantly larger seismic potency and propagation distance in the preferred direction, and clearly quantified by the directivity ratio derived from the second order moments of the spatio‐temporal distribution of slip rate. The macroscopic rupture asymmetry of the large‐scale pulses stems from the difference in the criticality conditions for self‐sustained propagation in each rupture direction, induced by the asymmetric normal stress changes operating in bimaterial interfaces. In contrast, crack‐like ruptures show macroscopic asymmetry under restrictive conditions. The discussed mechanism is robust with respect to regularization parameters, ranges of stress heterogeneities and a proxy for off‐fault yielding and should operate similarly for crustal‐scale rupture pulses even in the absence of velocity‐weakening. Small‐scale pulses, driven by the bimaterial normal stress reduction at the scale of the process zone, can detach from the rupture front of the large‐scale pulses that propagate in the preferred direction. However, their occurrence depends on the relaxation scale in the regularization of the normal stress response and their development can be hindered by off‐fault yielding.

Asymmetric rupture of large aspect‐ratio faults at bimaterial interface in 3D

“…[16] The foregoing results confirm the suggestion of Ampuero and Ben-Zion [2008] that macroscopic asymmetry can arise from bimaterial interface rupture whenever pulselike rupture develops, regardless of origin (i.e., whether the pulse mode arises from the frictional behavior, or, as in this study, from essentially geometrical effects such as sliding arrest due to edge diffractions). The geometrical mechanism identified here, while by itself only effective under a rather restricted range of initial conditions, may act in concert with velocity-dependent friction to enhance the effect of the latter.…”

“…Interesting new behaviors emerge when the friction is strongly velocity dependent, as suggested by recent experimental studies [e.g., Beeler et al, 2008], such that the friction coefficient falls to relatively low values immediately behind the rupture front, but can recover to near its initial value as sliding velocity falls thereafter. Ampuero and Ben-Zion [2008] show that a pulse mode of rupture is then possible under a fairly wide range of conditions, as already well established in the case of a homogeneous medium [e.g., Beeler and Tullis, 1996;Zheng and Rice, 1998]. In the bimaterial case, Ampuero and Ben-Zion show cases in which the negative-directed pulse decays in amplitude, or even stops entirely, while the positive-directed pulse remains self-sustained.…”

“…[2] Rupture at the interface between solids of contrasting elastic compliance has been the subject of extensive theoretical and numerical studies [e.g., Weertman, 1980;Adams, 1995;Andrews and Ben-Zion, 1997;Harris and Day, 1997;Cochard and Rice, 2000;Ranjith and Rice, 2001;Ma and Beroza, 2008;Ampuero and Ben-Zion, 2008], as well as scale-model experiments [Xia et al, 2005]. In a propagating mode II rupture, the compliance contrast induces a normal stress perturbation proportional to the slip gradient [Weertman, 1980], which can be large near the rupture front.…”

Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

“…Weertman 1980;Ben-Zion & Andrews 1998;Ampuero & Ben-Zion 2008;Brietzke et al 2009) suggest that earthquakes in the area tend to propagate to the northwest. This is consistent with observed directivities of small to moderate events on the section southeast of the array (Kurzon et al 2014;, along-strike Table 2.…”

On the efficient and reliable numerical solution of rate-and-state friction problems

“…These approaches have successfully reproduced a rich spectrum of earthquake and slow-slip-related behaviour (Liu & Rice 2005;Lapusta & Liu 2009) or spatial, temporal variations of seismic slip evolution on seismogenic faults (Lapusta et al 2000;Kato 2004;Kaneko et al 2010;Kato 2014) and fast velocity-weakening (Ampuero & Ben-Zion 2008) demonstrating the strengths of the strategies applied.…”