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

Earthscope板块边界观测站内地震的超低频电磁监测

• 批准号: 0346236
• 负责人: Simon Klemperer
• 金额: --
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-05-15 至 2011-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0346236&HistoricalAwards=false
• 关键词: Ultra; low; frequency; electromagnetic; monitoring

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.

按年计算，加州的地震每年造成数人死亡，并造成数十亿美元的财产损失。了解地震是否可预测是社会的自然利益；如果它们是可预测的，就开发方法来获得哪怕几分钟的预警。我们正试图通过研究电磁发射作为最有希望的潜在震前瞬态之一来解决这一社会需求。我们的监测站网络通过为公众提供独立的数据来源，补充了在加利福尼亚运行的磁监测站的商业“地震预报”服务。美国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以预测。我们正在北加州建立一个由三个超低频率电磁（ULF-EM）记录站点组成的网络，以便了解地震物理学并探测地震前瞬变（如果存在的话）。我们的电磁传感器包括超灵敏的磁铁，用来探测地球磁场的微小变化，以及低噪音的电缆，用来探测地球内部的微小电流。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探测仪器（应变仪和地震仪）进行交叉检查。我们所有的数据每天24小时不间断地传输到公共数据存档。我们每天都对仪器进行监控，以确认它们记录的数据是有效的，我们通过一套标准化的程序来运行数据，以搜索可能的异常情况。我们有可能在地震前识别出信号水平或特征的重大变化，但更有可能的是，在大地震发生后，我们将有一个有价值的数据集，我们可以用它来测试关于地震发生方式的假设，并帮助我们了解未来的地震周期。我们正在记录超低频电磁数据，因为世界上许多不同地区都报道了大地震（震级大于6.5）前后的超低频率（0.01-10赫兹）磁场异常。如果是真的，这些信号包含了有关地震物理的重要信息，特别是地震活动前后断层内部和周围的流体运动。我们将磁传感器与PBO应变仪和地震仪搭配使用，以便将地震信号与与传感器倾斜相关的工件分离开来。为了排除其他潜在的磁信号来源（包括人造信号），我们正在使用相同的、空间分开的记录器进行记录。需要在大地震发生之前、期间和之后以及空间上连续记录磁场和电场，以证明超低频电磁信号的存在与否。我们将ULF-EM的记录地点定位在圣安地列斯断层和旧金山湾区的其他主要断层上，因为这些断层在未来十年有发生大地震的巨大潜力。