Developing high-resolution tremor catalogs to constrain numerical models of slow slip

开发高分辨率震颤目录来约束慢滑移数值模型

• 批准号: 1344948
• 负责人: Allan Rubin
• 金额: $ 30万
• 依托单位: Princeton University
• 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: 2014-02-15 至 2018-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1344948&HistoricalAwards=false
• 关键词: Developing; resolution; tremor; catalogs; constrain

One of the major discoveries in geophysics in the past decade has been that of ?episodic slow slip and tremor? in many of the world?s subduction zones. Most known faults either slip steadily at the plate tectonic rate (a few centimeters per year), or spend most of the time ?locked? and slip only during short-lived earthquakes, with slip speeds of order 1 m/sec and propagation speeds of order 3 km/sec (the sound speed of rock). Slow slip events, on the other hand, have average slip speeds of only ~0.1 micron/s and propagate up to 300 km along strike at remarkably reproducible speeds of roughly 10 km/day. Coincident in time and space with the geodetically-observed slow slip is a seismic signal termed ?tectonic tremor?. Unlike typical earthquakes, which have impulsive seismic wave arrivals, tremor is a low-amplitude signal that can last for hours and that most often lacks clearly identifiable seismic wave arrivals. Slow slip has now been discovered in nearly all subduction regions with sufficient instrumentation to see it, if it were present. Tremor is coincident in space and time with may slow slip events, and has also been discovered on the deep extension of the San Andreas fault in California. In addition to representing a previously unrecognized style of fault slip, episodic slow slip is relevant to seismic hazards because it increases the stressing rate on the locked portions of faults capable of producing magnitude 9 earthquakes. It has also been proposed that it may delimit the down-dip extent of slip during those earthquakes (bringing, notably, strong ground shaking considerably closer to downtown Seattle than had previously been thought).Because the resolution of geodetic data for deep faults is quite poor, tremor locations currently provide our most detailed images of the space-time history of slow slip. But because tremor lacks clear wave arrivals and can be active on multiple regions of the fault simultaneously, it cannot be located using standard techniques. We are developing a new tremor detection algorithm that, applied to the subduction zone off the coast of the Pacific Northwest, is currently producing the most accurate tremor locations in the world. Rather than the more traditional method of comparing seismograms from different time windows at the same station, it compares the same time windows at different stations. Relative location errors are often less than 1 km, allowing us to image in great detail secondary tremor fronts that arise behind, and propagate 1?2 orders of magnitude faster than, the main front of the slow slip event. By imaging these secondary fronts and their relation to the main with high fidelity, we expect to learn more about the processes underlying slow slip. In addition, studies of tremor are proliferating worldwide, but as yet there is no single, generally-agreed-upon method for locating it. By comparing our location method with more traditional methods and combining aspects of each, we stand to learn much about how to improve tremor location algorithms and how to apply this knowledge in other regions.

过去十年中，地球物理学中的主要发现之一是情节的慢滑和震颤？在世界许多中，俯冲带。 大多数已知的故障要么以板块构造速率稳定下滑（每年几厘米），要么花费大部分时间？锁定？仅在短寿命的地震中滑动，其滑移速度为1 m/sec和3 km/sec（岩石的音速）的繁殖速度。 另一方面，慢滑动事件的平均滑动速度仅为〜0.1微米/s，并以大约10 km/天的可再现速度沿罢工沿罢工高达300 km。 时间和空间与大地观察到的缓慢滑动的巧合是被称为地震信号吗？构造震颤？与具有冲动的地震波到达的典型地震不同，震颤是一个低振幅信号，可以持续数小时，并且通常缺乏明显可识别的地震波到达。 如今，在几乎所有具有足够仪器的俯冲区域都发现了慢滑，如果存在的话。震颤在时空时与可能会减慢滑倒事件的速度是一致的，并且在加利福尼亚的圣安德烈亚斯断层的深度扩展中也发现了震颤。 除了代表以前未知的断层滑动风格外，情节慢滑道还与地震危害有关，因为它增加了能够产生9级地震的断层锁定部分的应力速率。 还提出，它可能会在这些地震期间划定跌落量的下垂程度（尤其是使强大的地面摇晃到西雅图市中心的震动比以前认为的更近得多）。因为目前，震颤的地理数据分辨出深层的地理数据是相当贫穷的，目前为我们提供了我们最详细的慢速滑移时空图像。但是，由于震颤缺乏透明波的到达，并且可以同时在故障的多个区域处活跃，因此不能使用标准技术定位。 我们正在开发一种新的震颤检测算法，该算法应用于西北太平洋沿岸的俯冲带，目前正在世界上生产最准确的震颤地点。 它不是更传统的方法来比较同一站点的不同时间窗口的地震图，而是比较不同站点的同一时间窗口。 相对位置误差通常小于1公里，使我们能够以详细的细节形象形象出现的次要震颤前部，并比慢滑态事件的主要前部传播1？2个数量级。 通过对这些次要战线进行成像及其与主忠诚的关系，我们希望更多地了解慢速滑移的过程。 此外，震颤的研究在全球范围内激增，但尚无定位的单一的，一般的方法。 通过将我们的位置方法与更传统的方法进行比较，并结合了每种方法，我们将了解如何改善震颤位置算法以及如何在其他地区应用这些知识。