Laboratory Insight Into Seismic Estimates of Energy Partitioning During Dynamic Rupture: An Observable Scaling Breakdown

Abstract

We investigate energy partitioning using seismological methods of seismic ruptures with estimated submicron levels of slip in the laboratory. Estimates inferred from recorded seismic waves are founded on microscale phenomenological friction experiments in the laboratory and appear to be constrained by inherent assumptions. In this concerted study, we build on the methods used to absolutely calibrate an array of piezoelectric transducers in a direct shear laboratory apparatus. We found that flat-broadband sensor behavior allowed us to study source extent parameters using spectral source models that are typically used to interpret small to moderate-sized earthquakes. We computed the corner frequencies, low-frequency plateaus, and high-frequency spectral falloff exponent using single-station assumptions. Moment magnitude ranged from −9<M w <−7.5 and slip was on the order of nanometers to micrometers-extending our understanding of source parameters studied via seismic waves. A number of findings are highlighted: (i) Variations in spectral falloff with corner frequencies followed the observations made in natural conditions. (ii) Corner frequency shift phenomenon was observed (f cP /f cS ∼ 1.34) and was attributed to source finiteness rather than wave propagation effects. (iii) Events were stress overshoot as determined by the Savage-Wood efficiency. (iv) The empirical power law scaling relationship between fracture energy and slip, given as G c ∝ū nG , where n G =1.28 appears to break down with seismological estimates made at the mining scale (n G =1.86) and laboratory scale (n G =2.35). This break in scaling may be related to the types of off-fault energy sinks that are inherently captured in the seismological interpretation of fracture energy. Key Points:• We analyzed localized seismicity produced along a weak preexisting fault in a direct shear friction apparatus • Calibration methods were employed to the spectral modeling of P and S waves, allowing for the quantitative estimates of source properties • Common empirical relationships between slip and effective fracture energy at natural scales were found to differ from mining and lab scales Supporting Information:• Supporting Information S1 Correspondence to: P. A. Selvadurai, paul.selvadurai@sed.ethz.ch Citation: Selvadurai, P. A. (2019). Laboratory insight into seismic estimates of energy partitioning during dynamic rupture: An observable scaling breakdown. SELVADURAI 11,355From the Omega models we can estimate the seismic moment given as

Rupture-dependent breakdown energy in fault models with thermo-hydro-mechanical processes

“…Some dynamic rupture simulations account for thermo-hydro-mechanical effects (Andrews, 2002;Bizzarri and Cocco, 2006;Noda et al, 2009;Schmitt et al, 2015) and/or incorporate the effects of inelastic off-fault damage (Dunham et al, 2011a, b;Roten et al, 2017;Withers et al, 2018) that should result in qualitatively similar effects on the breakdown energy. However, many employ simplified shear resistance evolutions that prescribe the breakdown energy and/or weakening rate directly, as a local fault property (Richards-Dinger and Dieterich, 2012;Shaw et al, 2018;Gallovic et al, 2019;Dalguer et al, 2020). Future work is needed to investigate whether and how the complexity of the local weakening and strengthening behavior experienced by the simulated faults with thermo-hydromechanical and other mechanisms can be translated into simulations with more simplified local relations, e.g., slipdependent relations, and still result in similar rupture dynamics.…”

Modeling precursory laboratory seismicity using a wear-based rate- and state-dependent friction model

“…Part (ii ) will help us reconcile the seismically observed laboratory foreshocks (P. A. Selvadurai, 2019). The RSF model investigates the concept that heterogeneity is a prerequisite for having synchronous slow and fast rupture on similar sections of a fault.…”

“…More detailed source analysis has been performed by P. A. Selvadurai (2019). (f ) Surface roughness measurement taken a posteriori using the longer length scale optical profilometer (Nanovea P50).…”

“…Brune, 1970Brune, , 1971 were already used to infer source properties for these emissions in a concerted study by P. A. Selvadurai (2019).…”

“…Seismic source properties were extracted from a quasi-dynamic RSF numerical model and compared to estimates made from the spectral analysis of the seismic waves in a supporting study (P. A. Selvadurai, 2019). With our frictional model we investigate some open questions: (i ) How does the level of strength heterogeneity or the evolving stress field affect rupture initiation, propagation and arrest?…”