Shear ruptures of extreme dynamics in laboratory and natural conditions

Abstract

In the Earth's crust shear ruptures are responsible for macroscopic dynamic failure causing earthquakes. Shear ruptures induced by and triggered by the mining-induced stress change sometimes result in damaging rockbursts. The fundamental mechanism of the shear rupture is critically linked to the magnitude of ground motion, and hence, any resulting damage. For the effective management of seismic hazard both from natural and mining-related causes, a comprehensive understanding of the fundamental mechanism of the shear rupture is crucial. In recent years it has been observed that shear ruptures can propagate with extreme velocities exceeding the shear wave speed. Experiments show that a remarkable feature of extreme ruptures is the fact that friction reduces toward zero in the rupture head. Coseismic reduction in friction is critical in accelerating the fault slip and to the magnitude of ground shaking which affects the amount of potential earthquake and rockburst damage. Despite the critical importance, physical processes which determine the dramatic weakening of friction are still unclear and continue to be vigorously debated. The second unresolved question is about the source of energy which provides extreme rupture dynamics. This paper shows that the nature of extreme ruptures in intact rocks and in pre-existing faults with frictional and coherent interfaces is the same. It demonstrates that in all types of extreme ruptures, the fault weakening can be explained by a recently-proposed shear rupture mechanism associated with the intensive tensile-cracking process in the rupture tip observed for all extreme ruptures. The tensile-cracking process creates, in certain conditions, a fan-like fault structure, the shear resistance of which is extremely low. The fan-structure represents the basis of a self-sustaining natural mechanism of stress intensification in the rupture head providing the driving power for rupture propagation with extreme velocities. The fan-mechanism causes dramatic embrittlement of intact hard rocks under high stress and makes transient strength of intact hard rocks during the rupture propagation significantly less than the frictional strength. This paper introduces features of the fan-mechanism operation in primary ruptures and in natural complex faults and proposes an alternative view on the nature of earthquakes and shear rupture rockbursts generated by extreme ruptures.

New physics of supersonic ruptures

“…Accepting this fact, the models were simplified by presenting the future fault as consisting of "predetermined" slabs. A detailed description of the physical and mathematical models is presented in previous papers (Tarasov, 2010(Tarasov, , 2014(Tarasov, , 2017(Tarasov, , 2019Tarasov & Guzev, 2013;Tarasov & Randolph, 2011Tarasov et al, 2017). This paper uses The structure of the future fault consists of a row of "predetermined" slabs (tiles) inclined at an angle α 0 to the rupture plane.…”

“…After the point of the fan structure characterized by σ t(max) has passed the growing crack, the crack growth stops due to the decrease in tensile stresses in the rear part of the fan structure (Supporting Information: Video S7). Tarasov (2017) discussed the role of the fan mechanism in the creation of off-fault tensile cracking in experiments conducted by Samudrala (2002) where the extreme shear ruptures were generated by impact loading.…”

“…Accepting this fact, the models were simplified by presenting the future fault as consisting of “predetermined” slabs. A detailed description of the physical and mathematical models is presented in previous papers (Tarasov, 2010, 2014, 2016, 2017, 2019; Tarasov & Guzev, 2013; Tarasov & Randolph, 2011, 2016, Tarasov & Sadovskii, 2016; Tarasov et al, 2017). This paper uses images of the models to illustrate different features of the fan structure.…”

“…Since the extraordinary features of the fan mechanism and the properties of rocks determined by it contradict the classic theories, the fan‐hinged approach was perceived with great difficulty and distrust. The problem is that in the brief papers published so far, it was impossible to present this extremely complex and extensive topic with clear arguments, reliable evidence, and detailed discussion (Tarasov, 2008, 2010, 2011, 2013, 2014, 2016, 2017, 2019; Tarasov & Guzev, 2013; Tarasov & Ortlepp, 2007; Tarasov & Potvin, 2013; Tarasov & Randolph, 2008, 2011, 2016; Tarasov & Sadovskii, 2016; Tarasov et al, 2016, 2017).…”

Fan‐hinged shear instead of frictional stick–slip as the main and most dangerous mechanism of natural, induced, and volcanic earthquakes in the earth's crust

“…Since extraordinary features of the fan mechanism and the properties of rocks determined by it are contradictory to the modern ideas, the fan‐hinged approach is viewed with great skepticism and distrust. The problem is that in the brief papers published so far, it was impossible to present this extremely complex and extensive topic with clear arguments, reliable evidence, and detailed discussion (Tarasov, 2008, 2010, 2011, 2013, 2014, 2016, 2017, 2019; Tarasov & Guzev, 2013; Tarasov & Ortlepp, 2007; Tarasov & Potvin, 2013; Tarasov & Randolph, 2008, 2011, 2016; Tarasov & Sadovskii, 2016; Tarasov et al, 2016, 2017).…”