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

研究人员建议实验分析地震滑动的启动，加速和自我修复的过程中，在一个补丁的表面上的故障。实验将在一种新的旋转剪切装置上进行，该装置允许测试沿沿着岩石块的摩擦滑动，以获得大的滑动（几米）、约1 m/s的滑动速度和高达30 MPa的法向应力。此外，该装置的设计允许在短时间段（最多5秒）内将有限量的存储能量（最多107 J/m2）施加在断层面上。他们的初步结果表明，这些条件可以产生一个类似地震的唇事件（ELSE）沿着岩石样品上升时间0.1秒，滑动速度高达1米/秒，滑动距离高达3米，和自我愈合（强度恢复和破裂停止）。他们建议使用该装置的独特功能，进行一系列广泛的ELSE实验，这些实验类似于原位加载条件下断层补丁的地震过程。这些实验将允许在实验室控制条件下分析基本地震参数，如上升时间，弱化，自愈，滑移速度，滑移距离，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（或显着减少）不稳定的粉碎大腿速度.开发并实现扭矩控制系统，使我们能够模拟大范围的地震活动。典型的地震从一个小的核开始，并作为一个快速移动的破裂前沿沿着断层面传播。在地震前，断层面上的每一个小块都处于静止状态，它被破裂前缘加速到约1 m/s的滑动速度，当震前储存的弹性能量被耗散后，它停止滑动。因此，贴片在几分之一秒到几秒的时间段内经历快速加速和减速。在此期间的激烈的加速/减速，补丁的摩擦变化显着没有稳态速度。另一方面，断层摩擦力的典型实验研究是为了确定地震时可能无法实现的稳态摩擦力，本研究利用俄克拉荷马州大学最近建造的一个装置的可扩展性，消除了这种基本的实验限制。该装置适用于模拟类似地震的事件，因为它可以加载一个实验室岩石补丁的能量存储在一个巨大的飞轮（225公斤）。这种独特的，先进的设计，我们的实验系统允许模拟地震破裂过程中的原位条件下（1）高应力和高速;（2）有限的能量供应;（3）应力和速度控制。所提出的实验将在实验、理论和地震概念之间提供更好的联系，并且，通过这样做，将显著地促进对地震破裂过程、地震能量平衡、断层弱化的物理学以及滑动速率、滑动量级和辐射能量的缩放的理解。

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.