An Experimental Perspective on the Formation of Pulverized Rocks During Transient Coseismic Dilatancy
Description:
Pulverized rocks are enigmatic fault damage zone structures frequently found in large, strike-slip fault zones and characterized by predominantly volumetric deformation due to intense, randomly-oriented mode I fractures. Their genesis has been associated broadly with transient normal stress changes near the propagating tip of earthquake ruptures. Past experiments have shown that brittle rock fabrics with properties similar to natural pulverized rocks can be formed by subjecting rock samples to large uniaxial compressive loads at rapid strain rates (>102 s-1), but the differential stresses and strain rates required are much larger than those expected in shallow fault damage zones during dynamic rupture. An alternative hypothesis is that pulverized rocks form during rapid, dilatational strains. Over the past few years, we have utilized a modified experimental configuration for a split Hopkinson Pressure Bar (SHPB) to simulate the fragmentation of rocks under isotropic tensile loads to study this alternative hypothesis. The experimental configuration replaces the uniform cylindrical specimen of traditional SHPB tests with a rock disk bonded between two lead disks. Axial compression of the sample causes radial expansion of the lead, which induces transversely isotropic tension in the rock disk. We use this experimental method to investigate damage accumulation by transient tensile loading in four different rock types, and over multiple earthquake cycles in Westerly granite. We show that the fracture patterns produced have many of the same properties as natural pulverized rocks, and the fracture density (A) varies as a function of lithology and (B) increases during each successive loading cycle. Our work suggests that pulverized rock can be produced under tension at strain rates as low as 10-3 s-1 or lower, and the fracture density and spatial extent may be controlled by the size of the coseismic tensile stress perturbation and the number of slip events on the fault.
Session: Above the Seismogenic Zone: Fault Damage and Healing in the Shallow Crust [Poster]
Type: Poster
Date: 4/19/2023
Presentation Time: 08:00 AM (local time)
Presenting Author: Ashley Griffith
Student Presenter: No
Invited Presentation:
Authors
Ashley Griffith Presenting Author Corresponding Author griffith.233@osu.edu Ohio State University |
Zachary Smith zachary_smith@berkeley.edu University of California, Berkeley |
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An Experimental Perspective on the Formation of Pulverized Rocks During Transient Coseismic Dilatancy
Category
Above the Seismogenic Zone: Fault Damage and Healing in the Shallow Crust