Seismological fracture or breakdown energy represents energy expended in a volume surrounding the advancing rupture front and the slipping fault surface. Estimates are commonly obtained by inverting ground motions and using the results to model slip on the fault surface. However, this practice cannot identify contributions from different energy‐consumption processes, so our understanding of the importance of these processes comes largely from field‐ and laboratory‐based studies. Here, we use garnet fragment size data to estimate surface‐area energy density with distance from the fault core in the damage zone of a deeply exhumed strike‐slip fault/shear zone. Estimated energy densities per fragmentation event range from 2.87 × 103to 2.72 × 105 J/m3in the outer and inner portions of the dynamic damage zone, respectively, with the dynamic zone being inferred from the fractal dimensions of fragment size distributions and other indicators. Integrating over the ∼105 m width of the dynamic damage zone gives fracture surface‐area energy per unit fault area ranging from a lower bound of 6.63 × 105 J/m2to an upper bound of 1.63 × 107 J/m2per event. This range overlaps with most geological, theoretical, and kinematic slip‐model estimates of energy expenditure in the source volume for earthquakes characterized by seismic moments >1017 N·m. We employ physics‐based fragmentation models to estimate equivalent tensile strain rates associated with garnet fragmentation, which range from 5.42 × 102to 1.04 × 104 s−1per earthquake in the outer and inner portions of the dynamic damage zone, respectively. Our results suggest that surface‐energy generation is a nonnegligible component of the earthquake energy budget.
Large strike‐slip faults experience numerous earthquakes during which transient tensile and compressive mean normal stress perturbations travel along opposing sides of the fault. Research exploring dynamic rock fracture through multiple earthquake cycles has focused predominantly on transient compressive loading, but little is known about off‐fault damage development due to successive tensile loading. We investigate damage accumulation by transient tensile loading over multiple earthquake cycles using a modified sample configuration for uniaxial compressive loading apparatuses consisting of a Westerly granite rock disk bonded to two lead disks. We show that fracture density increases during each successive loading cycle, and pulverized rock can be produced under tension at strain rates as low as 10−3s−1. Therefore, pulverized rock can form at low strain rates, and its texture and extent may be controlled by the size of the coseismic tensile stress perturbation and the number of slip events on the fault.
more » « less- NSF-PAR ID:
- 10443830
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 19
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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