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

在过去的十年里，天体物理学的一个重大发现是？间歇性缓慢滑动和震颤在世界上的许多？俯冲带。 大多数已知的断层要么以板块构造的速度（每年几厘米）稳定地滑动，要么花费大部分时间？锁上了？而滑动只发生在短寿命地震期间，滑动速度为1米/秒，传播速度为3公里/秒（岩石的声速）。 另一方面，慢滑动事件的平均滑动速度仅为~0.1微米/秒，并以大约10公里/天的可重复速度沿走向传播高达300公里。 在时间和空间上与大地测量观测到的慢滑动重合的是一种地震信号，称为？构造性震颤？与具有脉冲地震波到达的典型地震不同，震颤是一种低振幅信号，可以持续数小时，并且通常缺乏清晰可识别的地震波到达。 现在几乎在所有的俯冲带都发现了缓慢滑动，如果存在的话，有足够的仪器可以看到它。震颤在空间和时间上与可能的缓慢滑动事件相一致，并且在加州的圣安德烈亚斯断层的深延伸上也被发现。 除了代表一种以前未被认识到的断层滑动类型外，幕式缓慢滑动与地震灾害有关，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。 也有人提出，它可以界定在这些地震滑动下倾的范围（带来，值得注意的是，强烈的地面震动相当接近市中心的西雅图比以前认为的）由于深断层的大地测量数据的分辨率是相当差，震颤的位置目前提供了我们最详细的图像的时空历史的缓慢滑动。但是，由于震颤缺乏明确的波到达，并可能同时在断层的多个区域活动，因此无法使用标准技术进行定位。 我们正在开发一种新的震颤检测算法，应用于太平洋西北海岸的俯冲带，目前正在产生世界上最准确的震颤位置。 与比较同一台站不同时间窗的地震图的传统方法不同，它比较了不同台站的相同时间窗。 相对位置误差往往小于1公里，使我们能够在非常详细的图像二次震颤战线后面出现，并传播1？2个数量级，比主锋的慢滑事件。 通过对这些次级锋及其与主锋的关系进行高保真成像，我们希望更多地了解慢滑的过程。 此外，震颤的研究正在世界范围内激增，但到目前为止还没有一个单一的，普遍同意的方法来定位它。通过比较我们的定位方法与更传统的方法，并结合每个方面，我们站在学习如何改进震颤定位算法，以及如何将这些知识应用于其他地区。

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.