Whether or not energy dissipation is localized in the vicinity of the rupture tip, and whether any distal energy dissipation far from the crack tip has a significant influence on rupture dynamics are key questions in the description of frictional ruptures, in particular regarding the application of Linear Elastic Fracture Mechanics (LEFM) to earthquakes. These questions are investigated experimentally using a 40-cm-long experimental frictional interface. Three independent pistons apply a normal load with a fourth piston applying a shear load, enabling the application of a heterogeneous stress state and stress barriers. After loading the frictional interface to a near-critical state, subsequent unloading of one normal-load piston leads to dynamic ruptures which propagate into the heterogeneous stress fields. The ruptures in these experiments are found to be driven by unconventional singularities, characterized by an ever-increasing breakdown work with slip, and as a result do not conform to the assumptions of LEFM. As these experimental stress barriers inhibit slip, they therefore also reduce the breakdown work occurring outside of the cohesive zone. It is shown that this distal weakening, far from the crack tip, must be considered for the accurate prediction of rupture arrest length. These experiments are performed in the context of a proposed stimulation technique for Enhanced Geothermal Systems (EGSs). It has previously been suggested, through theoretical arguments, that stress barriers could be induced through the manipulation of pore pressure such that there is reduced seismic hazard during the shear stimulation of EGSs. This stimulation technique, known as preconditioning, is demonstrated here to reduce the mechanical energy flux to the crack tip, G, while also increasing the fracture energy, Gc. Preconditioning is shown to be capable of arresting seismic rupture and reducing co-seismic slip, slip velocity, and seismic moment at preconditioning stresses which are reasonably achievable in the field. Due to the fully-coupled nature of seismic rupture and fault slip, preconditioning also reduces distal weakening and its contribution to the propagation of induced seismic ruptures. In a similar vein, heterogeneous pore pressure fields associated with some seismic swarms can be used to explain changes in stress drop within the swarm without recourse to material or total-stress heterogeneity.

中文翻译：

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应力屏障对非常规奇点驱动的摩擦破裂的影响


能量耗散是否局限于断裂尖端附近，以及远离裂纹尖端的任何远端能量耗散是否对破裂动力学有显着影响是摩擦破裂描述中的关键问题，特别是关于线性弹性断裂力学 （LEFM） 在地震中的应用。使用 40 cm 长的实验摩擦界面对这些问题进行了实验研究。三个独立的活塞施加法向载荷，第四个活塞施加剪切载荷，从而能够应用异质应力状态和应力屏障。在将摩擦界面加载到接近临界状态后，随后卸载一个正常载荷活塞会导致动态破裂，并传播到非均质应力场中。这些实验中的破裂被发现是由非常规奇点驱动的，其特征是不断增加的滑移分解功，因此不符合 LEFM 的假设。由于这些实验应力屏障会抑制滑移，因此它们也减少了发生在内聚区之外的击穿功。结果表明，必须考虑这种远离裂纹尖端的远端弱化，才能准确预测破裂阻滞长度。这些实验是在为增强型地热系统 （EGS） 提出的增产技术的背景下进行的。以前通过理论论证，人们已经提出，可以通过操纵孔隙压力来诱导应力屏障，从而减少 EGS 剪切增产过程中的地震危险。 这里展示了这种被称为预处理的增产技术，可以减少流向裂纹尖端 G 的机械能通量，同时增加断裂能量 Gc。预处理被证明能够阻止地震破裂并减少在现场可以合理实现的预处理应力下的共震滑移、滑移速度和地震力矩。由于地震破裂和断层滑移的完全耦合性质，预处理还可以减少远端减弱及其对诱发地震破裂传播的贡献。同样，与一些地震群相关的非均质孔隙压力场可用于解释地震群内应力下降的变化，而无需求助于材料或总应力非均质性。