Nonlinear dynamical triggering of slow slip on simulated earthquake faults with implications to Earth

Abstract

Among the most fascinating, recent discoveries in seismology are the phenomena of dynamically triggered fault slip, including earthquakes, tremor, slow and silent slip—during which little seismic energy is radiated—and low frequency earthquakes. Dynamic triggering refers to the initiation of fault slip by a transient deformation perturbation, most often in the form of passing seismic waves. Determining the frictional constitutive laws and the physical mechanism(s) governing triggered faulting is extremely challenging because slip nucleation depths for tectonic faults cannot be probed directly. Of the spectrum of slip behaviors, triggered slow slip is particularly difficult to characterize due to the absence of significant seismic radiation, implying mechanical conditions different from triggered earthquakes. Slow slip is often accompanied by nonvolcanic tremor in close spatial and temporal proximity. The causal relationship between them has implications for the properties and physics governing the fault slip behavior. We are characterizing the physical controls of triggered slow slip via laboratory experiments using sheared granular media to simulate fault gouge. Granular rock and glass beads are sheared under constant normal stress, while subjected to transient stress perturbation by acoustic waves. Here we describe experiments with glass beads, showing that slow and silent slip can be dynamically triggered on laboratory faults by ultrasonic waves. The laboratory triggering may take place during stable sliding (constant friction and slip velocity) and/or early in the slip cycle, during unstable sliding (stick‐slip). Experimental evidence indicates that the nonlinear‐dynamical response of the gouge material is responsible for the triggered slow slip.

Numerical Modeling of Dynamically Triggered Shallow Slow Slip Events in New Zealand by the 2016 Mw 7.8 Kaikoura Earthquake

“…The low effective normal stress of the fault zone being dynamically triggered is consistent with lab experiment of dynamic triggering of earthquakes (Johnson et al, 2012). The stress perturbations of 65-100 kPa associated with dynamic triggering of SSEs in this study are higher than the typical range of 1-5 kPa observed in studies of the dynamic triggering of earthquakes in volcanic/geyser regions in California (Aiken & Peng, 2014;Brodsky & Prejean, 2005) and nonvolcanic tremors near Parkfield (Peng et al, 2009), but comparable to the level of transient shear stresses (40-60 kPa) triggering nonvolcanic tremors in subduction zones (Rubinstein et al, 2007) and continental thrust faults (Peng & Chao, 2008).…”

A Dynamic-induced Direct-shear Model for Dynamic Triggering of Frictional Slip on Simulated Granular Gouges

“…This observation is similar to the previous results from the static triggering of frictional slip on filling gouges, such as the maximum shear stress of a fault zone under a static shear load increases with increasing normal stress [31]. The compaction state of filling gouges is thus importantly related to fault stability [2,32]. Additionally, we can observe that the frictional slip is partially recovered after a P-wave incidence ( Fig.…”

“…Johnson and Jia [24] found that the dynamic triggering either further weakens a layer of filling gouges or induces the frictional slip when the gouge layer is near failure. The frictional slip is also related to the nonlinear dynamic response of filling gouges [2]. Furthermore, the dynamic triggering of frictional slip is a complex process that may be also associated with other factors, for instance, tectonic pressure, initial state of filling gouges and wave transmission and reflection from adjacent rock discontinuities.…”

“…Rock discontinuities are structural breaks in geological media, such as faults, bedding planes, joints and microcracks. The connection between rock discontinuities and seismic activities has been recognized as a central issue of dynamic triggering of frictional slip [1,2], nevertheless, remains enigmatic. The dynamic triggering of frictional slip may take place close to or far from a main shock and depends on incident wave energy and stored strain energy at a discontinuous plane.…”

“…Several laboratory experiments have been conducted to explore the mechanism of frictional slip at a range of slip rates, with and without gouges and under the effects of temperature, normal and pore pressures [2,[4][5][6]. The experimental configurations include uniaxial compression [7,8], biaxial compression [4,9], triaxial compression [10][11][12], direct-shear [5,[13][14][15], double direct-shear [16][17][18] and rotary shear [6,19].…”