Thermal runaway is a ductile localization mechanism that has been linked to deep-focus earthquakes and pseudotachylyte formation. In this study, we investigate the dynamics of this process using one-dimensional, numerical models of simple shear deformation. The models employ a visco-elastic rheology where viscous creep is accommodated with a composite rheology encompassing diffusion and dislocation creep as well as low-temperature plasticity. To solve the nonlinear system of differential equations governing this rheology, we utilize the pseudo-transient iterative method in combination with a viscosity regularization to avoid resolution dependencies. To determine the impact of different model parameters on the occurrence of thermal runaway, we perform a parameter sensitivity study consisting of 6,000 numerical experiments. We observe two distinct behaviors, namely a stable regime, characterized by transient shear zone formation accompanied by a moderate (100–300 K) temperature increase, and a thermal runaway regime, characterized by strong localization, rapid slip and a temperature surge of thousands of Kelvin. Nondimensional scaling analysis allows us to determine two dimensionless groups that predict the model behavior. The ratio $t_{\mathrm{r}}/t_{\mathrm{d}}$ represents the competition between heat generation from stress relaxation and heat loss due to thermal diffusion while the ratio $U_{\text{el}}/U_{\text{th}}$ compares the stored elastic energy to thermal energy in the system. Thermal runaway occurs if $t_{\mathrm{r}}/t_{\mathrm{d}}$ is small and $U_{\text{el}}/U_{\text{th}}$ is large. Our results demonstrate that thermal runaway is a viable mechanism driving fast slip events that are in line with deep-focus earthquakes and pseudotachylyte formation at conditions resembling cores of subducting slabs.

中文翻译：

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由于热失控导致的快速延性应变局部化


热失控是一种延性局部化机制，与深源地震和假速晶石的形成有关。在本研究中，我们使用简单剪切变形的一维数值模型研究了该过程的动力学。该模型采用粘弹性流变学，其中粘性蠕变与包含扩散和位错蠕变以及低温塑性的复合流变学相适应。为了求解控制这种流变学的非线性微分方程组，我们利用伪瞬态迭代方法与粘度正则化相结合，以避免分辨率依赖性。为了确定不同模型参数对热失控发生的影响，我们进行了由 6,000 次数值实验组成的参数敏感性研究。我们观察到两种不同的行为，即稳定状态，其特征是瞬态剪切带形成，伴随适度（100-300 K）温度升高，以及热失控状态，其特征是强局域化、快速滑移和数千度的温度激增。开尔文。无量纲缩放分析使我们能够确定预测模型行为的两个无量纲组。 比率$t_{\mathrm{r}}/t_{\mathrm{d}}$代表应力松弛产生的热量与热扩散产生的热量损失之间的竞争，而该比率$U_{\text{埃尔}}/U_{\text{th}}$将系统中存储的弹性能与热能进行比较。如果发生热失控$t_{\mathrm{r}}/t_{\mathrm{d}}$很小并且$U_{\text{埃尔}}/U_{\text{th}}$很大。我们的结果表明，热失控是驱动快速滑移事件的可行机制，该机制与深源地震和类似俯冲板片核心条件下的假速滑石形成一致。