Comprehensive Analyses of Cascadia Tremor and Slow Slip

卡斯卡迪亚震颤和慢滑的综合分析

• 批准号: 1358512
• 负责人: Kenneth Creager
• 金额: $ 50.91万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1358512&HistoricalAwards=false
• 关键词: Comprehensive; Analyses; Cascadia; Tremor; Slow

Slow slip and tremor are key processes in tectonic plate motion in subduction zones, one of which is positioned along the Pacific Northwest coast from Cape Mendocino up to Vancouver Island in Canada. For the basic mechanics of subduction zones to be understood, slow slip must be made to yield its secrets. Progress in this puzzle in the past decade has been and will continue in the future to be transformative. To understand these processes, this project is analyzing the copious seismic and geodetic data that has been gathered over the past decade. Different data types and analysis approaches are being integrated to determine more precisely where and when strain is accumulating and the role of slow slip in loading and releasing plate-interface stress.The potential interaction of slow slip with the hazardous locked portions of subduction zones mandates better understanding of slow slip phenomena. For example, the next generation of Pacific Northwest seismic hazard maps will use our estimates of the updip limit of tremor as one way to estimate the downdip limit of megathrust rupture, refining estimates of the shaking across the west coast in the next great American earthquake. In addition, it is possible that the slow slip being observed and interpret may reveal changes in the seismic hazard over time as motion changes pattern, accelerates and decelerates.The investigators are involved in the operation of the regional seismic network and are active in various forms of outreach to educate the public about seismic hazard. Episodic tremor and slip events is providing a golden opportunity to advance public awareness of the regional geological environment and seismic hazard through blogs, TV and newspaper interviews and NOVA documentaries. The University of Washington has captured seven episodes of slow slip under northern Washington since 2004 with seismic arrays two with the EarthScope Array of (eight) Arrays, accumulating a rich dataset.Several approaches are being integrated to sift through the mountain of continuous recordings and our growing catalogs in search of key relationships. The foci in this work is (1) delineation of the space-time progression of tremor by both beam backprojection and envelope correlation methods, (2) precise tracking of slow slip with LFE locations and recurrence, (3) systematic determination of tremor amplitude and its relation to tidal stressing and amount of slip, (4) integration of GPS and strainmeter timeseries with spatio-temporal constraints from tremor, and (5) comparison of emerging ivory-tower slow-slip models with observation. These approaches allow refinement of the relation of tremor propagation patterns such as rapid tremor reversals and streaks to slip front propagation and low frequency earthquake generation, and thus yield constraints on the slip velocities, propagation velocities, and rise times of slow slip pulses. As well, this study is teasing out how much slow slip extends updip from tremor, with implications for seismic hazard, and to assess the importance of tremor amplitude in scaling tremor duration to slow slip moment release.Currently in hand are growing caches of several types of geophysical data: multiple catalogs of tremor ranging from Cascadia-wide with 210,000 tremor locations to high-resolution locations collected by the Array of Arrays, as well as a burgeoning catalog of low-frequency earthquakes. These provide views from the 1000 km to 100 m scales. In addition, GPS, strain, and tilt-meter time series record deformation more directly. Linking the above datasets is leading to characterization of the inferred propagation of slow slip fronts over a range of spatial and temporal scales.

缓慢滑动和地震是俯冲带中构造板块运动的关键过程，其中之一位于沿着太平洋西北海岸从加拿大的门多西诺角到温哥华岛。 为了了解俯冲带的基本力学，必须进行缓慢滑动以揭示其秘密。 在过去十年中，这一难题的进展已经并将在未来继续是变革性的。 为了理解这些过程，该项目正在分析过去十年收集的大量地震和大地测量数据。 不同的数据类型和分析方法正在被整合，以更精确地确定应变在哪里和何时积累，以及缓慢滑动在加载和释放板界面应力中的作用。缓慢滑动与俯冲带危险锁定部分的潜在相互作用要求更好地理解缓慢滑动现象。 例如，下一代的太平洋西北部地震危险图将使用我们对地震上倾极限的估计，作为估计巨型逆冲断层破裂下倾极限的一种方法，改进对下一次美国大地震中西海岸震动的估计。 此外，随着运动模式的改变、加速和减速，正在观察和解释的缓慢滑动可能揭示地震危险随时间的变化，调查人员参与了区域地震网络的运作，并积极开展各种形式的外联活动，向公众宣传地震危险。 间歇性的地震和滑动事件提供了一个黄金机会，通过博客、电视和报纸采访以及NOVA纪录片来提高公众对区域地质环境和地震灾害的认识。自2004年以来，华盛顿大学利用地震阵列（2个）和EarthScope阵列（8个），已经捕获了华盛顿北方下的七次缓慢滑动，积累了丰富的数据集。 本研究的重点是（1）通过波束反投影和包络相关方法描绘震颤的时空进程，（2）通过LFE位置和重现精确跟踪缓慢滑动，（3）系统确定震颤幅度及其与潮汐应力和滑动量的关系，（4）整合GPS和应变仪时间序列与震颤的时空约束，（5）象牙塔慢滑模型与观测的比较。 这些方法允许细化的震颤传播模式，如快速的震颤反转和条纹的关系，以滑动前的传播和低频地震的产生，从而产生的滑动速度，传播速度和上升时间的慢滑动脉冲的约束。 此外，这项研究还梳理出了从震颤向上倾斜延伸的缓慢滑动的程度，以及对地震危险的影响，并评估了在将震颤持续时间换算为缓慢滑动力矩释放时震颤振幅的重要性。目前，我们手头上有越来越多的几种类型的地球物理数据：多个震颤目录，范围从具有210，000个震颤位置的卡斯卡迪亚范围到由阵列阵列收集的高分辨率位置，以及一个新兴的低频地震目录。 这些提供了从1000公里到100米尺度的视图。 此外，GPS、应变和倾斜仪时间序列更直接地记录变形。 将上述数据集联系起来，可以在一定的空间和时间尺度上对慢滑锋的推断传播进行表征。