Exploring the influence of tidal stress changes on the generation of secondary slip fronts during slow slip events in Cascadia

地球内部的能量在断层上释放，这些断层可能会突然破裂，导致危险的地震，也可能会在持续数小时至数年的大规模地震事件中缓慢滑动。 在卡斯卡迪亚经常发生慢滑现象，这是对下一次大规模逆冲地震将发生的锁定区域下方板块界面沿着条件的响应和修改。 控制慢滑行为的特定物理过程也决定了最靠近太平洋西北部主要人口中心的潜在破裂面的状态。区分不同的流变模型和机械处理，已被提出来解释慢滑是具有挑战性的，因为他们中的许多人可以重现慢滑事件的主要特征，如传播速度，应力降，和复发间隔。这使得所有能够重现这些特征的模型都同样可信。 最近发现的“二次”滑动前发生在一起的慢滑提供了一个新的机会，以区分竞争的模式。因此，该项目将通过确定次级滑动锋的空间范围、滑动速度和应力降来表征次级滑动锋。 然后将这些诊断与模拟的二次滑动锋进行比较，以确定哪种竞争模型配方能够重现观测结果，并提供一个窗口，以了解太平洋西北部下方不断变化的断层条件。慢滑现象要求滑动速率增加到观测速度，通常是板块速率的10到100倍，但避免加速到足以产生地震波。 负责实施这一速度限制的具体物理机制存在争议。 我们的研究结合了观测和理论成分，以研究潮汐应力变化对慢滑过程的影响，从而提供了一个客观的测试几个竞争的模型治疗，成功地再现了一阶特性的慢滑（例如滑动速度，应力下降等）。拟议的观测工作将使用来自卡斯卡迪亚的低频地震数据集的主成分分析，系统地量化紧随主滑动锋通过的次级锋的长度尺度、时间尺度、传播速度和传播方向。 理论上的努力将纳入剪切和正常的应力振荡到慢滑模拟，包括速率和状态的配方和淬火硬化。 我们收集的观测目录将用于测试和改进模型处理，以寻求预测和实际特性之间的一致性，沿着沿着卡斯卡迪亚巨型推力传播的次级锋。

Energy within the Earth is released on faults that can either rupture abruptly, causing hazardous earthquakes, or slip slowly in largely aseismic events that can last from hours to years. Slow-slip phenomena occur frequently in Cascadia, responding to and modifying conditions along the plate interface beneath the locked region where the next mega-thrust earthquake will occur. The specific physical processes that govern slow-slip behavior also determine the state of the potential rupture surface nearest to the major population centers in the Pacific Northwest. Discriminating between the different rheological models and mechanical treatments that have been proposed to explain slow slip is challenging because many of them can reproduce the primary characteristics of slow slip events, such as propagation speeds, stress drops, and recurrence intervals. This makes all models that can reproduce these features equally plausible. The recent discovery of "secondary" slip fronts that occur in conjunction with slow slip provides a new opportunity to distinguish between competing models. Accordingly, this project will characterize secondary slip fronts by determining their spatial extents, slip velocities, and stress drops. These diagnostics will then be compared with modeled secondary slip fronts to determine which of the competing model formulations is able to reproduce the observations and provide a window into changing fault conditions beneath the Pacific Northwest. Slow-slip phenomena require the slip rate to increase to observed speeds, typically 10 to 100 times the plate rate, but refrain from accelerating fast enough to generate seismic waves. The specific physical mechanisms responsible for imposing this speed limit are in dispute. Our research combines observational and theoretical components to examine the influence of tidal stress changes on slow-slip processes, thereby offering an objective test of several competing model treatments that have succeeded in reproducing the first-order characteristics of slow slip (e.g. slip speeds, stress drops, etc.). The proposed observational effort will use Principle Component Analysis on a low-frequency earthquake dataset from Cascadia to systematically quantify the length scales, time scales, propagation speeds, and propagation directions of secondary fronts that immediately follow passage of the main slip front. The theoretical effort will incorporate shear and normal stress oscillations into slow-slip simulations that include rate-and-state formulations and dilatancy hardening. The observational catalog that we assemble will be used to test and refine model treatments that seek agreement between predicted and actual characteristics of secondary fronts that propagate along the Cascadia mega-thrust.