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

卡斯卡迪亚俯冲带物质特性的高分辨率成像

• 批准号: 1520690
• 负责人: Daniel Lizarralde
• 金额: $ 43万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-11-01 至 2019-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1520690&HistoricalAwards=false
• 关键词: Resolution; Imaging; Material; Properties; Cascadia

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.

北方加州、俄勒冈州和华盛顿近海的卡斯卡迪亚海底地带能够产生毁灭性的9级地震。 由于我们还没有用现代仪器观测到这样的大地震，地震学界对这样的地震的细节有很大的不确定性。 对这类地震的危险性估计在很大程度上取决于破裂向陆地传播的距离。 目前，这是最好的估计破裂的计算机模型依赖于匹配的GPS数据，以验证控制模型行为的材料属性分布。 本研究将使用一个新的，结合在岸-离岸数据集，调查材料属性的详细空间变化沿着主要卡斯卡迪亚逆冲断层。研究结果将有望为未来断裂的计算机模型提供信息，并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公里远）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，这些物理性质是这些断层模型中假设的典型强度分布的基础。 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（~ 1 km）断层带内，流体压力发生了下倾变化。主要的断层力学模型通常假设在锁定区的底部有效正应力的不连续性（1个数量级的变化）。 然而，这还没有在分辨率上进行观测评估，需要看到断层带或跨越锁定蠕动边界，这需要海上数据。他们还将研究是否有任何证据表明，在俯冲的戈尔达板块地幔的断层带内普遍存在蛇纹石化。这两种类型的研究将有可能通过最近部署的社区地震实验在南部卡斯卡迪亚俯冲带的陆上和海上，其中包括一个地区的卡斯卡迪亚逆冲界面丰富的微震活动，并使用现代技术来确定地震位置，地震计时钟校正和环境噪声技术。