High-Resolution Imaging of Material Properties in the Cascadia Subduction Zone

北加州、俄勒冈州和华盛顿州近海的卡斯卡迪亚俯冲带能够产生破坏性的9级地震。由于我们还没有用现代仪器观测到这些大地震中的一次，地震学界对于这样一场地震的详细情况有很大的不确定性。这类地震的危险性估计很大程度上取决于断裂向岸上传播的距离。目前，这是最好的估计，通过计算机模型的破裂依赖于匹配的GPS数据来验证控制模型行为的材料属性分布。这项研究将使用一个新的陆上和海上联合数据集来研究Cascadia主逆冲断层沿线物质性质的详细空间变化。研究结果有望为未来断裂的计算机模型提供信息，也将为整个科学界提供新的数据。研究的总体目标是了解卡斯卡迪亚俯冲带内活动变形断层的强度分布。在下行板块内破裂的断层真的比紧邻的（约5公里外）锁定逆冲界面强两个数量级吗？虽然我们不能直接测量应力，但研究人员可以测量相关的物理特性，这些物理特性是这些断层模型中假设的典型强度分布的基础。该项目的主要目标是确定是否有证据表明在直接（~1km）断裂带内流体压力会发生下倾变化，从而产生逆冲界面地震活动。主要断层力学模型通常假定锁断带底部的有效正应力不连续（1个数量级的变化）。然而，这还没有在观测上进行评估，需要看到断裂带或跨越锁定蠕动边界的分辨率，这需要海上数据。他们还将研究是否有证据表明，在俯冲的戈达板块地幔的断裂带内普遍存在蛇纹岩化现象。这两种类型的研究都可能通过最近部署的陆上和海上社区地震实验来完成，该实验覆盖了卡斯卡迪亚俯冲带的一个区域，该区域具有丰富的微地震活动，并使用现代技术来确定地震位置，地震仪时钟校正和环境噪声技术。

The Cascadia Subuction Zone offshore of Northern California, Oregon, and Washington is capable of generating devastating magnitude 9 earthquakes. Since we have not observed one of these great earthquakes with modern instrumentation, the seismological community has significant uncertainties about what such an earthquake will look like in detail. Hazard estimates for this type of earthquake are very dependent on how far onshore the rupture propagates. Currently this is best estimated by computer models of the rupture which rely on matching GPS data to validate the material property distributions that control the model behavior. This study will use a new, combined onshore-offshore dataset to investigate the detailed spatial variations in material properties along the main Cascadia thrust fault. The results will hopefully inform the computer models of future ruptures and will also provide new data to the entire scientific community.The overall goal of the study is to understand the distribution of strength on actively deforming faults within the Cascadia subduction zone. Are the faults that rupture within the downgoing slab really two orders of magnitude stronger than the immediately adjacent (~5km away) and locked thrust interface? While we cannot measure stress directly, the researchers can measure related physical properties that underlie the typically strength distributions assumed in models of these faults. The primary project goals are to determine if there is any evidence for a downdip change of fluid pressure within the immediate (~1km) fault-zone producing thrust interface seismicity. Leading fault mechanics models typically assume a discontinuity (1 order of magnitude change) in effective normal stress at the base of the locked zone. However, this has not been observationally evaluated at the resolution need to see the fault-zone or across the locked-creeping boundary which requires offshore data. They will also examine whether there is any evidence for pervasive serpentinization within the fault-zones in the mantle of the subducting Gorda Plate. Both of these types of studies will be made possibly by the recently deployed, community seismic experiments onshore and offshore in the Southern Cascadia subduction zone which cover the one region of the Cascadia thrust interface with abundant microseismicity, and the use of a modern techniques for determining earthquake locations, seismometer clock corrections and ambient noise techniques.