Ultra-low frequency electromagnetic monitoring of earthquakes within the Earthscope Plate Boundary Observatory

按年率计算，加州的地震每年造成数人死亡，造成数十亿美元的财产损失。了解地震是否可预测是一种自然的社会利益；如果地震是可预测的，那么就开发出即使是几分钟预警的方法。我们正试图通过研究电磁辐射作为地震前最有希望的潜在瞬变之一来满足这一社会需求。我们的监测站网络通过为公众提供独立的数据来源，补充了在加州运营磁性监测站的商业“地震预报”服务。国家科学基金会的板块边界观测站(PBO)的部分任务是了解地震是否可预测。我们正在加利福尼亚州北部建立一个由三个超低频电磁(ULF-EM)记录点组成的网络，以了解地震物理并检测地震前的瞬变(如果存在)。我们的电磁传感器包括用于检测地球磁场微小变化的超灵敏磁铁，以及用于检测地球内部微小电流的低噪音电缆。我们的ULF-EM传感器与现有的PBO站点配置在一起，因此我们的电磁传感器上观察到的任何异常都可以与更传统的地震检测仪器：应变仪和地震仪进行交叉检查。我们的所有数据都会24小时不间断地传输到公共数据档案馆。我们每天监控我们的仪器，以确认它们正在记录有效数据，并通过一套标准化程序运行数据，以搜索可能的异常情况。我们有可能识别出地震前信号水平或特征的重大变化，但更有可能的是，在大地震之后，我们将拥有一个有价值的数据集，我们可以用它来检验有关地震启动方式的假设，并帮助我们了解未来的地震周期。我们记录超低频电磁数据是因为世界上许多不同地区都报告了大地震(大于6.5级)前后的超低频(0.01-10赫兹)磁场异常。如果是真的，这些信号包含有关地震物理的重要信息，特别是在地震活动之前、期间和之后断层内和断层周围的流体运动。我们正在将我们的磁性传感器与PBO应变仪和地震仪配置在一起，以便将来自地震的信号与与传感器倾斜相关的人工制品分开。我们使用相同的、空间分离的记录器进行记录，以排除其他潜在的磁信号源(包括人造信号)。需要连续记录大地震之前、期间和之后的磁场和电场，并在空间上接近大地震，以证明超低频电磁信号的存在或不存在。我们正在沿着圣安德烈亚斯和旧金山湾区的其他主要断层寻找我们的超低频电磁记录地点，因为这些断层很有可能在未来十年发生大地震。

On an annualized basis, earthquakes in California kill several people and cause several billions of dollars of property damage every year. There is a natural societal interest in understanding whether earthquakes are predictable; and if they are predictable, developing ways to obtain even a few minutes of warning. We are attempting to address this societal need by studying electromagnetic emissions as one of the most promising potential pre-seismic transients. Our network of monitoring stations complements commercial "earthquake prediction" services operating magnetic monitoring stations in California by providing an independent source of data for the public. Part of the mission of the National Science Foundation's Plate Boundary Observatory (PBO) is to learn whether earthquakes are predictable. We are building a network of three ultra-low frequency electromagnetic (ULF-EM) recording sites in northern California in order to understand earthquake physics and to detect pre-seismic transients if they exist. Our electromagnetic sensors include ultra-sensitive magnets to detect tiny changes in Earth's magnetic field, and low-noise electric cables to detect tiny electric currents inside the Earth. Our ULF-EM sensors are collocated with existing PBO sites, so that any anomalies observed on our electromagnetic sensors can be cross-checked against more-conventional earthquake detection instruments: strain meters and seismographs. All our data is transmitted to a public data archive on a continuous basis, 24 hours a day. We monitor our instruments on a daily basis to confirm that they are recording valid data, and we run the data through a set of standardized programs to search for possible anomalies. It is possible that we will recognize a major change in signal levels or character before an earthquake, but it is more likely that after a major earthquake we will have a valuable dataset that we can use to test hypotheses about the way earthquakes initiate, and to help us understand future earthquake cycles.We are recording ULF-EM data because ultra-low frequency (0.01-10 Hz) magnetic field anomalies prior to and following large earthquakes (magnitude greater than 6.5) have been reported from a number of different regions of the world. If real, these signals contain important information about the physics of earthquakes, particularly fluid motion in and around the fault before during and after seismic activity. We are collocating our magnetic sensors with PBO strain-meters and seismometers in order to allow signals from earthquakes to be separated from artifacts related to sensor tilt. We are recording with identical, spatially separated recorders in order to exclude other potential sources of magnetic signals (including man-made signals). Continuous recording of the magnetic and electric field before, during and after, and spatially close to, a significant earthquake, is required to demonstrate the reality or absence of ULF-EM signals. We are locating our ULF-EM recording sites along the San Andreas and other major faults in San Francisco Bay Area, because these faults have a large potential for a major earthquake in the next decade.