Experimental simulation of earthquake rupture processes

地震破裂过程的实验模拟

• 批准号: 1345087
• 负责人: Ze'ev Reches
• 金额: $ 25万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1345087&HistoricalAwards=false
• 关键词: Experimental; simulation; earthquake; rupture; processes

An earthquake occurs when a fault in the earth crust ruptures abruptly. The rock blocks that bound the fault, slip for tiny distance in small earthquakes, and up to a few meters in large events. During this slip, the fault weakens and the weakening provides energy to continue the earthquake rupture. Obviously, this is a complex process in which the mechanical properties of the fault drastically change within seconds. Classical experimental approaches to explore these processes are conducted at constant velocity or at very slow velocity; neither of these conditions is relevant to the rupture of natural earthquakes. We propose a new experimental approach that is anticipated to reveal key parameters that are relevant to earthquakes. These experiments will utilize the unique capabilities of energy supply and power control of our earthquake laboratory in the University of Oklahoma. The impact of these capacities was demonstrated in the preliminary work that succeeded in simulations of fault behavior during earthquakes up to magnitude M=8 (similar to 1906 San Francisco earthquake). Why are such experiments important? First, in general, better understanding of earthquake processes is essential for the reduction of seismic hazard. Second, this study is particularly important for the calculations of seismic ground shaking, which are used for building structural design. These calculations are based on the mechanical behavior of faults during earthquakes, and more accurate and relevant calculations require better knowledge of this behavior. Theoretical models suggest that earthquake rupture is a complex process with non-trivial evolution of kinematic and dynamic properties (e.g., Tinti et al. 2005). Recent experiments that simulated the velocity history of actual earthquakes (e.g., Sone and Shimamoto, 2009; Fukuyama and Mizoguchi, 2010; Liao, Chang and Reches, in revision for EPSL) show that constitutive relations which were determined in low-velocity, short-distance friction experiments do not necessarily hold for variable, high slip-velocity of natural earthquakes. The present objective is to simulate the earthquake rupture process by loading experimental faults similarly to earthquake loading, and to derive the constitutive relation at these conditions. The experiments will be conducted with a high-speed rotary shear apparatus that applies frictional sliding along rock blocks under slip-velocity up to 1 m/s, normal stress up to 30 MPa, and large slip distance. This apparatus has two unique capabilities: (1) Loading the experimental fault by a finite amount of energy (up to 10^7 J/m^2) that is stored in a flywheel (Chang et al., 2012); and (2) A real-time feedback system that controls the power-density applied on the fault (power-density = slip velocity * shear-stress). These methods allow the application of any loading history to reveal the fault response under transient earthquake loading. The preliminary results of both methods show strong similarities to theoretical models of fault behavior in terms of the evolution of fault strength (weakening and strengthening), slip velocity, energy dissipation, and rise-time. We will link the observed constitutive relations to the mechanisms of fault weakening, and for this purpose, we will characterize the fault properties with ultramicroscopic methods (AFM, XRD, SEM, and TEM).

当地壳中的断层突然破裂时，就会发生地震。岩石块绑定了故障，在小地震中​​滑倒，在大事件中最多只有几米。在此滑动过程中，断层减弱和弱化为继续地震破裂提供了能量。显然，这是一个复杂的过程，其中故障的机械性能在几秒钟内发生了巨大变化。探索这些过程的经典实验方法以恒定速度或速度非常缓慢进行。这些条件都与自然地震破裂有关。我们提出了一种新的实验方法，预计将揭示与地震相关的关键参数。这些实验将利用俄克拉荷马大学地震实验室的能源供应和电力控制的独特功能。在初步工作中证明了这些能力的影响，该工作成功地模拟了地震期间的断层行为，直至M = 8（类似于1906年的旧金山地震）。为什么这样的实验很重要？首先，通常，对地震过程的更好理解对于减少地震危险至关重要。其次，这项研究对于用于构建结构设计的地震地面震动的计算尤其重要。这些计算基于地震期间故障的机械行为，更准确，相关的计算需要更好地了解这种行为。 理论模型表明，地震破裂是一个复杂的过程，具有运动和动态特性的非平凡进化（例如，Tinti等人，2005年）。模拟了实际地震速度历史的最新实验（例如Sone和Shimamoto，2009; Fukuyama and Mizoguchi，2010; liao，chang and receins for Epsl的修订版）表明，在低速度，短速度，短速度，短效率，短效率，短 - 级别，短速度，短效率，短速度，短速度， - 距离摩擦实验不一定要适用于自然地震的可变，高速速度。目前的目的是通过与地震负荷相似的实验断层来模拟地震破裂过程，并在这些条件下得出构造关系。 实验将采用高速旋转剪切设备进行，该设备沿岩石块沿岩石块施加摩擦滑动，最高为1 m/s，正常应力高达30 MPa，并且较大的滑动距离。该设备具有两种独特的功能：（1）通过存储在飞轮中的有限能量（最多10^7 J/m^2）加载实验断层（Chang等，2012）； （2）一个实时反馈系统，该系统控制在故障上施加的功率密度（功率密度=滑移速度 *剪切压力）。这些方法允许应用任何加载历史记录来揭示瞬态地震加载下的故障响应。两种方法的初步结果都在断层强度（弱化和强化），滑移速度，能量耗散和上升时间的角度方面均与断层行为的理论模型相似。我们将观察到的本构关系与断层弱的机制联系起来，为此，我们将使用超显微镜方法（AFM，XRD，SEM和TEM）表征断层特性。