Pulse-like and crack-like ruptures in experiments mimicking crustal earthquakes

Abstract

Theoretical studies have shown that the issue of rupture modes has important implications for fault constitutive laws, stress conditions on faults, energy partition and heat generation during earthquakes, scaling laws, and spatiotemporal complexity of fault slip. Early theoretical models treated earthquakes as crack-like ruptures, but seismic inversions indicate that earthquake ruptures may propagate in a self-healing pulse-like mode. A number of explanations for the existence of slip pulses have been proposed and continue to be vigorously debated. This study presents experimental observations of spontaneous pulse-like ruptures in a homogeneous linear-elastic setting that mimics crustal earthquakes; reveals how different rupture modes are selected based on the level of fault prestress; demonstrates that both rupture modes can transition to supershear speeds; and advocates, based on comparison with theoretical studies, the importance of velocityweakening friction for earthquake dynamics.earthquake physics ͉ mechanics of faulting ͉ rupture modes ͉ shear cracks ͉ velocity-dependent friction D estructive large earthquakes occur as dynamic frictional ruptures along preexisting interfaces (or faults) in the Earth's crust. Inversions of seismic and other field observations have significantly advanced our understanding of earthquake ruptures. At the same time, detailed inversions often are impossible due to limited data availability or limited knowledge of the structure and properties of the crust. Numerical modeling of earthquakes helps pinpoint potential rupture scenarios but, in turn, requires a number of still poorly known inputs that are being actively researched. Such inputs include fault friction laws and initial stress conditions. This reality highlights the need for highly instrumented laboratory experiments that reproduce some of the basic physics governing rupture dynamics of crustal earthquakes while preserving enough simplicity so that clear conclusions can be obtained by direct observation. One example of such experiments is the work of Xia et al. (1, 2), which has demonstrated the ability of spontaneous dynamic ruptures to transition from sub-Rayleigh to supershear speeds. In the present study, we use their experimental configuration to investigate conditions leading to the selection of pulse-like vs. crack-like rupture modes in a setting that mimics crustal earthquakes. The geometry, loading, and nucleation mechanism are essentially 2D. This configuration is relevant for understanding the dynamics of large strike-slip earthquakes, which are dominated by in-plane sliding, and constitutes an experimental equivalent of 2D in-plane or Mode II numerical models of dynamic rupture, which are common in earthquake studies (3)(4)(5)(6)(7)(8)(9)(10)(11)(12).Numerical simulations in models that involve homogeneous elastic and interface properties and velocity-independent fault strength result in the crack-like mode of earthquake propagation, in which the duration of slip at each point on the fault is comparable to t...

Thermo- and hydro-mechanical processes along faults during rapid slip

“…That is consistent with a range of calculations for different stress levels and forms of τ ss (V ); crack-like ruptures are not found, only self-healing slip pulses, when τ b 0 < τ pulse . The guidelines just outlined on when self-healing versus crack-like ruptures occur are also consistent with laboratory studies in which both types of ruptures were generated in different conditions (Lykotrafitis et al, 2006;Lu et al, 2007).…”

Rupture Process of the 1999 Mw 7.1 Duzce Earthquake from Joint Analysis of SPOT, GPS, InSAR, Strong-Motion, and Teleseismic Data: A Supershear Rupture with Variable Rupture Velocity

“…Lu et al (2007) have shown that this mechanism can be generalized and that the supershear transition can occur under various conditions such as when patches with lower static strength, high prestress, or a preexisting subcritical crack meet the P and S waves in front of the crack. Dunham et al (2003) proposed a barrier mechanism where rupture is first delayed by a high strength barrier, which then starts rupturing and leads to a supershear rupture due to stress concentration from the breaking of the barrier.…”

“…A rough fault is expected to favor pulselike ruptures with the rise time being only a small fraction of the total duration of the earthquake (Beroza and Mikumo, 1996;Nielsen et al, 2000). Recent experimental work (Lu et al, 2007) has shown that for smooth faults, both cracklike ruptures (where rise time is similar to total rupture duration) and self-healing pulses are possible depending on the prestress on the fault. Another outstanding and related issue concerns the influence of slip heterogeneity on the spectrum of the radiated seismic waves and near-source ground motion.…”

Magnetic properties of fault pseudotachylytes in granites

“…The temperature interval through which a cooling pseudotachylyte may block a weak field TRM is at most a few hundreds of degrees and requires only a few seconds. Pulse-like seismic slip, such as that observed in experiments [Lu et al, 2007] could slightly expand this interval to tens of seconds.…”