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

调查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震动进行研究。最初，他们将把重点放在加利福尼亚州安扎附近的地震搜索上，该地区位于加利福尼亚州南部一个仪器密集的地区，拥有地面和井下连续地震数据。这些高质量的数据将被用来确定在安扎附近发生的震动的频率、内容和持续时间，从而允许未来根据这些特征进行搜索。然后，将使用自动地震检测方案在5年时间段内搜索所有SCSN站的地震。这些努力为解决有关加州非火山地震所必需的物理条件的基本问题奠定了基础。他们还将确定震动是否与当地地震、远程地震波到达、固体潮或慢滑或无地震蠕变的观测有关。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。这一建议中要解决的主要问题是：1)地震主要发生在发育良好的贯通断层上，如圣安德烈亚斯断裂带或圣哈辛托断裂带？2)非俯冲带地震主要发生在可能处于条件稳定的断层区域，例如：a)在浅层沉积物中深度小于5公里和/或b)在孕震带之下的地壳断层上深(15-20公里)？3)加州的地震时间是否受压力事件控制，如远震波的通过，当地地震率的变化，或潮汐作用力？如果是这样的话，触发地震所需的应力幅度和周期是多少？地震是最近才在连续记录的地震数据中发现的低幅度、持续时间长的地震信号。对地震的首次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。自那以后，全球各地的多个板块边界都观察到了地震，最近一次是沿着加利福尼亚州的几个断层。地震通常发生在断层深处，位于地震期间破裂的地壳下方。事实证明，震动是一系列地震和大地测量现象的一部分，可能与断层上的深部滑动有关。通过研究地震发生的细节，包括通常观察到地震的时间和地点，在什么条件下可以触发地震，以及地震和常规地震之间的关系，我们可以利用地震数据来研究更深层次的断层的摩擦特性。

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.