Exploring Deep Fault Mechanics by Identifying Non-Volcanic Tremor on Southern California Faults

研究人员将利用南加州地震台网（SCSN）提供的连续地震数据，对南加州的非火山地震进行研究。最初，他们将把我们的搜索重点放在加利福尼亚州安扎附近的震颤上，这是加利福尼亚州南部一个仪器密集的地区，那里有地面和钻孔连续的地震数据。这些高质量的数据将用于确定安扎附近发生的震颤的频率、内容和持续时间，从而使未来的搜索能够调整到这些特征。然后将使用自动地震探测方案在5年的时间内搜索所有SCSN站点的地震。这些努力为解决有关加利福尼亚非火山性震颤的必要物理条件的基本问题提供了基础。他们还将确定震颤是否与当地地震、远震波到达、地球潮汐或慢滑或地震蠕变观测有关。而且，他们将确定震颤的发生是否与已知的断层几何形状或材料特性有关。该提案需要解决的主要问题是：1)地震是否主要发生在发育良好的断层上，如圣安德烈亚斯或圣哈辛托断裂带？2)非俯冲带震颤是否主要发生在可能处于条件稳定的断层区域，例如：a)浅层沉积物深度小于5公里和/或b)发震带下方地壳断层深度（15 -20公里）？3)加州地震发生的时间是否受到诸如远震波的通过、当地地震活动频率的变化或潮汐力等压力事件的控制？如果是，触发震颤所需的应力振幅和周期是多少？震颤是最近才在连续记录的地震资料中发现的低振幅、长持续时间的地震信号。第一次对地震的观测是在日本进行的，发现地震发生在俯冲板块界面的深处。从那以后，在全球多个板块边界都观察到了震颤，最近一次是在加利福尼亚的几个断层上。地震通常发生在断层深处，在地震中地壳破裂的部分之下。事实证明，这种震颤是一系列地震和大地测量现象的一部分，可能与断层上的深滑动有关。通过研究地震发生的细节，包括通常在何时何地观察到地震，在什么条件下可以触发地震，以及地震与常规地震之间的关系，我们可以比以前使用地震数据更深入地研究断层的摩擦特性。

The investigator will undertake a study of non-volcanic tremor in southern California using continuous seismic data made available by the Southern California Seismic Network (SCSN). Initially, they will focus our search for tremor near Anza, California in a densely instrumented region of southern California that has both surface and borehole continuous seismic data. These high-quality data will be used to determine the frequency content and duration of tremor that occurs near Anza allowing for tuning of future searches to these features. An automatic tremor detection scheme will then be used to search for tremor across all SCSN stations over a 5-year time period. These efforts provide the foundation to address fundamental questions about physical conditions necessary for non-volcanic tremor in California. They will also determine whether tremor is correlated with local earthquakes, teleseismic wave arrivals, Earth tides, or observations of slow slip or aseismic creep. And, they will determine whether tremor occurrence correlates with known fault geometries or material properties. The major questions to be addressed in this proposal are: 1) Does tremor occur primarily along well-developed, through-going faults such as the San Andreas or San Jacinto fault zones?; 2) Does non-subduction zone tremor occur primarily in regions of a fault that are likely to be in conditionally stable such as: a) at depths less than 5 km in shallow sediments and/or b) deep (15 -20 km) on crustal faults beneath the seismogenic zone?, and 3) Is timing of tremor in California controlled by stressing events such as the passage of teleseismic waves, changes in local seismicity rates, or tidal forces? If so, what is the stress amplitude and period required to trigger tremor?Tremor are low amplitude, long duration seismic signals that have been only recently discovered in seismic data recorded continuously. The first observations of tremor were made in Japan and found to occur deep on the subducting plate interface. Tremor has since been observed at multiple plate boundaries around the globe, most recently along several faults in California. Tremor typically occurs deep on faults, below the portion of the crust that ruptures during an earthquake. It turns out that tremor is part of a suite of seismic and geodetic phenomena likely associated with deep slip on faults. By studying the details of tremor occurrence, including when and where tremor is typically observed, under what conditions tremor can be triggered, and the relationship between tremor and regular earthquakes, we can investigate the frictional properties of faults to greater depths than was previously possible using seismic data.