Development of an integrated Borehole Geodetic and Seismic Sensor: Project Completion

集成钻孔大地测量和地震传感器的开发：项目完成

• 批准号: 1955127
• 负责人: Mark Zumberge
• 金额: $ 14.95万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-03-01 至 2022-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1955127&HistoricalAwards=false
• 关键词: Development; integrated; Borehole; Geodetic; Seismic

Seismometers measure the shaking of the ground caused by earthquakes, ranging in intensity from tiny tremors undetectable by humans to large damaging earthquakes that pose a hazard to structures and people. It is the very small shaking from nearby sources, or the ultra-low frequency vibration following large events that cause the Earth to ring like a bell for many days afterward, that are difficult to capture. We are constantly trying to improve seismometers to be able to record this wide range of signals. Studying them can provide much information about what is inside the Earth. Seismic waves are the "light" that lets us see inside the Earth and seismometers are the "eyes" that let us create images of the internal Earth structure. In addition to shaking, earthquakes and related phenomena cause slow, gradual deformation of Earth's crust. To detect these deformations, extremely precise sensors are needed. Two types of deformation are often searched for: a very slight change in the position of the ground with respect to local vertical, called "tilt," and elongation or compression of the ground, called "strain." These are not unrelated, but the types of signals caused by tectonic activity are normally extremely small – measured by parts per billion in both tilt and strain. This Division of Erath Science Instrumentation and Facilities Program award supports development of a highly sensitive optical detection method and instrument to measure the motion of masses suspended by pendulums or a spring in a housing cemented into the bottom of a borehole. Optical fibers send laser light down to the sensor housing and return the light after it has been reflected from mirrors attached to the masses. By analyzing this light with electronics and a small computer located outside the borehole, the researchers can detect motions of the masses comparable to the diameter of individual atoms, and therefore detect both small seismic shaking and deformation of the ground caused by earthquake-related activity. As the investigators learn more about earthquake processes, the better are the chances of one day making precise forecasts of where and when they might occur.Support from this award will allow for fabrication and installation of a borehole system that utilizes optical-fiber interferometry to provide in one borehole: (a) a broadband vertical seismometer/gravimeter, (b) a broadband two-component horizontal seismometer/tiltmeter, and (c) a low-noise vertical long baseline strainmeter. The combined system will be able to measure vertical and horizontal ground velocities, gravity, tilt, and strain with sensitivities that compare favorably with any existing system over time scales from 10 Hz to many days; the downhole components are entirely passive, giving a long instrument lifetime and resistance to high downhole temperatures. The instrument is to be installed in an existing borehole at Pinon Flat Observatory for testing and comparison with the seismic and strain systems already operated there. The combined instrument promises an alternative to multi-instrument observations from independent seismometers, GPS receivers, gravimeters, tiltmeters and strain meters. The seismic observations are anticipated to meet the current requirements of Global Seismographic Network stations and geodetic measurements would offer lower noise observations than GPS at periods shorter than weeks. Target applications could include studies of the dynamics of crustal deformation including slow slip events, continuous and episodic slip, and other Earth movements that are known to occur but which do not generate damaging earthquakes. A deployed instrument could help to understand the effects of magmatic and subsurface fluid dynamics (e.g., hydrocarbon extraction and CO2 sequestration) on crustal deformation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地震仪测量地震引起的地面震动，其强度范围从人类无法察觉的微小震动到对建筑物和人员造成危害的大型破坏性地震。它是来自附近源的非常小的震动，或超低频振动。在导致地球像钟声一样响了很多天的重大事件之后，我们不断尝试改进地震仪，以便能够记录如此广泛的信号，研究它们可以提供有关地震的大量信息。里面的地震波是让我们看到地球内部的“光”，地震仪是让我们创建地球内部结构图像的“眼睛”。除了震动之外，地震和相关现象还会导致地球缓慢、逐渐的变形。为了检测这些变形，通常需要极其精确的传感器来寻找两种类型的变形：地面相对于局部垂直位置的非常轻微的变化，称为“倾斜”，以及地壳的伸长或压缩。这些并不是不相关的，但由构造活动引起的信号类型通常非常小——以十亿分之一的倾斜和应变来衡量。该部门的地球科学仪器和设施计划奖项支持开发。一种高灵敏度的光学检测方法和仪器，用于测量由固定在钻孔底部的外壳中的摆或弹簧悬挂的质量的运动。光纤将激光发送到传感器外壳，并在反射后返回光。从通过使用位于钻孔外的电子设备和小型计算机分析这些光，研究人员可以检测到与单个原子直径相当的质量的运动，从而检测到引起的小地震震动和地面变形。随着研究人员对地震过程了解得越多，有一天对地震可能发生的地点和时间进行精确预测的机会就越大。该奖项的支持将允许制造和安装利用钻孔系统。光纤干涉测量在一个钻孔中提供：（a）宽带垂直地震仪/重力仪，（b）宽带双分量水平地震仪/倾斜仪，以及（c）低噪声垂直长基线应变仪。测量垂直和水平地面速度、重力、倾斜和应变，其灵敏度在 10 Hz 到许多天的时间范围内优于任何现有系统；井下组件完全是无源的，该仪器将安装在 Pinon Flat 天文台的现有钻孔中，用于测试并与那里已运行的地震和应变系统进行比较。该组合仪器有望成为多仪器的替代方案。来自独立地震仪、GPS 接收器、重力计、倾斜计和应变计的观测 地震观测预计将满足全球地震网络站的当前要求，并且大地测量将在比 GPS 更短的周期内提供更低的噪声观测。目标应用可能包括地壳变形动力学的研究，包括慢滑移事件、连续和间歇性滑移以及已知发生但不会产生破坏性地震的其他地球运动，部署的仪器可以帮助了解地壳变形的影响。岩浆和地下流体动力学（例如，碳氢化合物提取和二氧化碳封存）对地壳变形的影响。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。