Testing the Thermal Shear Instability Hypothesis for Deep Slab Seismicity

检验深板地震活动的热剪切不稳定假说

• 批准号: 2121800
• 负责人: Magali Billen
• 金额: $ 38.63万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-01 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2121800&HistoricalAwards=false
• 关键词: Testing; Thermal; Shear; Instability; Hypothesis

EDITDeep earthquakes occur 100 to 680 km below Earth’s surface within cold tectonic plates that are sinking back into the Earth’s interior. There has been one prevailing theory for the cause of these earthquakes, called transformational faulting, but this theory is not able to explain all the observations related to deep earthquakes. Recently, research has indicated that another mechanism, called thermal shear instability (TSI), or a combination of both mechanisms, may be better able to match the observations. This research will use simulations of sinking tectonic plates (“slabs”) to determine the temperature, stresses, and rates of deformation at differentdepths/locations in the slab. These conditions will then be used as the starting conditions of a second type of simulation that can model TSI. We expect that for some conditions TSI (i.e., an “earthquake”) will occur, while at other conditions it will not. Therefore, using the output of the second type of model we can map out where in the slab TSI is a possible mechanism for deep earthquakes. If our hypothesis is correct, the shift in understanding of the mechanism causing f deep earthquakes (from one, to multiple potential mechanisms) would likely lead to new research aimed at directly linking seismic observations to the rupture properties of deep earthquakes. Broadly speaking, these results will further our understanding of the processes and conditions that lead to earthquake rupture.Recent modeling of, and laboratory measurements on, the conditions needed for thermal shear instability (TSI) have demonstrated that TSI may be a viable mechanism for deep earthquakes in subducting tectonic plates at depths up to around 150 km. At the same time, analysis of the magnitude-frequency distribution of deep earthquakes from 150-680 km has also been used to argue that TSI plays a role in triggering deep earthquakes, especially in warmer slabs. This project will test the viability of TSI as a mechanism for triggering deep earthquakes within subducting tectonic plates at depths of 100-680 km. This will be done in a three-step process. First, we will run 2D visco-elasto-plastic models for multiple profiles and subduction zones with different geometry, plate ages, rates of subduction, and rates/spatial variability of deep seismicity. The models will use a visco-elasto-plastic rheology and will be run for 0.1-1.0 my to determine a quasi-steady state spatial distribution and magnitude of elastic stresses, and total strain rate in the slab. Second, we will separately run 1D TSI models using the range of pressure, temperature, stress, and strain-rate conditions from the 2D slab models to determine at which conditions, present in the slab, TSI occurs. The TSI models will use the same rheology as the 2D subduction models. This comparison will demonstrate where in the slab TSI is potential triggering mechanism for deep earthquakes. Finally, we will compare location-specific earthquake observations (spatial distribution, focal mechanisms, magnitudes, b-values) to the model results (spatial distribution of TSI, fault orientations, estimates of magnitudes and geometric constraints on seismicity statistics). This comparison of the combined model results to observations will demonstrate how well our simulations capture the overall deformation of the slab at the short timescales of earthquake rupture up through the longer time-scales that determine the present-day stress-state in the slab.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在冷构造板中，地震发生在地球表面下方100至680公里，这些地震落在地球内部的冷层中。出于这些地震的原因，有一个流行的理论称为变革性断层，但是该理论无法解释与深层地震有关的所有观察结果。最近，研究表明，另一种称为热剪切不稳定性（TSI）的机制或两种机制的组合可能可以更好地匹配观测值。这项研究将使用下沉的构造板（“平板”）的模拟来确定平板中不同深度/位置的变形的温度，应力和变形速率。然后，这些条件将用作可以建模TSI的第二种模拟的起始条件。我们希望在某些情况下，TSI（即“地震”）将发生，而在其他情况下则不会。因此，使用第二种模型的输出，我们可以绘制出平板TSI中的位置是深层地震的可能机制。如果我们的假设是正确的，那么对引起深层地震的机制的理解转移（从一个，到多种潜在的机制）可能会导致新的研究，旨在将地震观测直接与深层地震的破裂特性联系起来。从广义上讲，这些结果将进一步我们对导致地球脉冲的过程和条件的理解。对实验室测量和实验室测量，对热剪切不稳定性（TSI）所需的条件（TSI）证明，TSI可能是俯冲构造台层中深层地板的可行机制。同时，对从150-680 km的深层脉冲的幅度频率分布的分析也被用来争辩说TSI在触发深层果肉中起着作用，尤其是在较温暖的平板中。该项目将测试TSI的生存能力，作为在100-680 km深度的构造板中触发深层地震的机制。这将在三步过程中完成。首先，我们将运行2D Visco-elasto塑料模型，用于具有不同几何形状，板年龄，俯冲速率以及深层地震性的速率/空间变异性的多个轮廓和俯冲带。这些模型将使用Visco-Elasto-Plasto-plastic流动性，并以0.1-1.0的方式运行，以确定弹性应力的准态态空间分布和弹性应力的大小，以及平板中的总应变速率。其次，我们将使用2D平板模型的压力，温度，应力和应变率条件范围单独运行1D TSI模型，以确定在板块中存在哪些条件，TSI发生。型号。这种比较将证明在板TSI中的位置是深层地震的潜在触发机制。最后，我们将将特定于位置的地震观测（空间分布，焦点机制，磁化率，B值）与模型结果（TSI的空间分布，断层方向，幅度的估计值和对地震统计的几何约束）进行比较。合并模型结果与观察结果的这种比较将证明我们的模拟在地震破裂的短时间内捕获了平板的总体变形，这通过较长的时间尺度来确定平板中当今的压力状态的较长时间尺度。该奖项在法定的任务中反映了NSF的法定任务，并通过评估了基础构成基础的范围，并反映了支持的支持者。