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

加利福尼亚州北部、俄勒冈州和华盛顿州近海的卡斯卡迪亚减震带有能力引发毁灭性的9级地震。由于我们没有用现代仪器观测到这样的大地震中的一次，地震界对这样的地震的细节会是什么样子有很大的不确定性。对这类地震的危险性估计在很大程度上取决于破裂在陆地上传播的距离。目前，这最好是通过破裂的计算机模型来估计的，计算机模型依赖于匹配的GPS数据来验证控制模型行为的材料特性分布。这项研究将使用一个新的陆上和近海相结合的数据集来调查沿着主要的卡斯卡迪亚逆冲断层的物质特性的详细空间变化。这一结果有望为未来破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。这项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。在下行板内破裂的断层真的比紧邻的(约5公里外)和锁定的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性质，这些性质是这些断层模型中假定的典型强度分布的基础。该项目的主要目标是确定是否有任何证据表明，在产生逆冲界面地震活动的直接(约1公里)断裂带内，流体压力发生了向下倾斜的变化。主要的断层力学模型通常假定锁定带底部的有效正应力不连续(变化1个数量级)。然而，这还没有在需要看到断裂带或跨越需要近海数据的锁定蠕变边界的分辨率下进行观测评估。他们还将检查是否有任何证据表明，在俯冲的戈达板块的地幔中的断裂带内存在普遍的蛇纹岩作用。这两种类型的研究都可能通过最近在卡斯卡迪亚南部俯冲带陆上和近海部署的社区地震实验进行，该实验覆盖了卡斯卡迪亚冲断界面具有丰富微震活动的一个区域，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.