Evolution of Pulverized Fault Zone Rocks by Dynamic Tensile Loading During Successive Earthquakes

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 10−3 s−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. Plain Language Summary Earthquakes produce transient compressive and tensile stresses on either side of the rupture. Fault damage accumulates during multiple earthquake cycles associated with these events. Damage accumulation due to successive compressive loading has been explored through rock mechanics experiments, but similar experiments under tension have been challenging to produce. We use a new experimental technique for subjecting a rock sample to repeated tensile loading cycles to explore how damage accumulates due to successive loading through multiple earthquakes. Our experiments show that fracture density in rock increases during each successive tensile loading event, and this is an effective mechanism for the formation of pulverized fault zone rocks. Key Points Fracture density increases and fragment size decreases during each successive tensile loading event Tensile pulverization of crystalline rock does not require high strain rates and can be produced tens of meters from large faults Finely pulverized rock may represent the accumulation of damage by successive earthquakes over thousands to millions of years