Analysis of fault rupture processes by earthquake-like slipevents in the laboratory

研究人员建议对断层表面斑块上地震滑动的启动、加速和自愈过程进行实验分析。实验将在一种新的旋转剪切仪上进行，该仪器可以测试沿岩石块的大滑动(几米)、滑动速度~1m/S和法向应力高达30兆帕的摩擦滑动。此外，该装置的设计允许在短时间内(高达5 S)在断层表面施加有限的储存能量(高达107J/m2)。他们的初步结果表明，在这些条件下，可以沿岩样产生类似地震的唇形事件(ELSE)，上升时间为0.1S，滑动速度可达1m/S，滑动距离可达3m，并具有自愈(强度恢复和破裂阻止)。他们建议利用这种设备的独特能力进行一系列广泛的其他实验，这些实验类似于现场加载条件下断层带上的地震过程。这些实验将能够在实验室控制的条件下分析基本的地震参数，如上升时间、减弱、自愈、滑动速度、滑动距离、产热和能量耗散。该项目的目标是在两个主要方面提高仪器的能力：1.加强加载框架，以消除(或显著减少)不稳定的高速破碎。开发和实施扭矩控制系统，使我们能够模拟大范围的地震情景。典型的地震始于一个小核，并作为快速移动的破裂前锋沿着断层表面传播。地震前断裂面上的每一块都处于静止状态，被破裂前锋加速到约1米/S的滑动速度，当震前储存的弹性能量耗散后停止滑动。因此，补丁在几分之一秒到几秒的时间内经历突然的加速和减速。在这段强烈的加减速过程中，在没有定常速度的情况下，补片摩擦力发生了剧烈的变化。另一方面，断层摩擦的典型实验研究旨在确定在地震中可能无法实现的稳态摩擦。所提出的研究通过利用俄克拉荷马大学最近建造的设备的独特能力，消除了这一基本实验限制。该装置适合于模拟类似地震的事件，因为它可以通过储存在一个巨大的飞轮(225公斤)中的能量来加载实验室岩石块。我们实验系统的这种独特、先进的设计允许在(1)高应力和高速度；(2)有限能量供应；以及(3)应力和速度控制的现场条件下模拟地震破裂过程。拟议的实验将在实验、理论和地震概念之间提供更好的联系，并通过这样做，将极大地促进对地震破裂过程、地震能量平衡、断层弱化的物理以及滑动速率、滑动强度和辐射能量的定标的理解。

The investigators propose to analyze experimentally the processes of initiation, acceleration and self-healing of seismic slip at a patch on the surface of a fault. The experiments will be conducted on a new rotary shear apparatus that allows testing frictional sliding along rock blocks for large slip (a few meters), slip-velocity of ~1 m/s, and normal stress up to 30 MPa. Further, the design of this apparatus allows application of a finite amount of stored energy on a fault surface (up to 107 J/m2) for a short period of time (up to 5 s). Their preliminary results show that these conditions can generate an Earthquake-Like lip Event (ELSE) along the rock sample with rise time 0.1 s, slip velocity up to 1 m/s, slip-distance up to 3 m, and self-healing (strength recovery and rupture arrest). They propose to use the unique capabilities of this apparatus for an extensive series of ELSE experiments that are analogous to earthquake processes at a fault patch under in-situ loading conditions. These experiments will allow analyzing fundamental earthquake parameters, such as rise-time, weakening, self-healing, slip velocity, slip distance, heat generation and energy dissipation under laboratory-controlled conditions.The objectives of the project is to improve the apparatus capabilities in two main aspects:1. Stiffening of the loading frame to eliminate (or significantly reduce) the unstable shattering athigh velocities.2. Develop and implement the torque control system that will allow us to simulate a wide range ofearthquake scenarios.A typical earthquake starts at a small nucleus and propagates as a fast movingrupture front along a fault surface. Every patch on the fault surface is at rest before the earthquake, it isaccelerated to slip velocity of about 1 m/s by the rupture front and it stops slipping when the elasticenergy that was stored prior to the earthquake has been dissipated. Thus, the patch experiences abruptacceleration and deceleration over periods from a fraction of a second to a few seconds. During thisperiod of intense acceleration/deceleration, the patch friction changes dramatically without steady-statevelocity. On the other hand, typical experimental studies of fault friction are designed to determine thesteady-state friction that probably does not realized during earthquakes.The proposed research eliminates this fundamental experimental limitation by utilizing the uniquecapabilities of an apparatus that was built recently in University of Oklahoma. Theapparatus is suitable to simulate earthquake-like events as it can load a laboratory rock patch by energystored in a massive flywheel (225 kg). This unique, advanced design of the our experimental systemallows simulating earthquake rupture processes under in-situ conditions of (1) high stress and highvelocity; (2) finite energy supply; and (3) stress and velocity control. The proposed experiments willprovide better links between experiments, theory and seismic concepts, and, by doing so, willsignificantly advance the understanding of earthquake rupture processes, earthquake energy balance,physics of fault weakening, and the scaling of slip rates, slip magnitude, and radiated energy.