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

地震仪测量地震引起的地面震动，强度从人类无法察觉的微小震动到对建筑物和人员构成危险的大破坏性地震不等。 很难捕捉到的是来自附近震源的非常小的震动，或者是大事件之后的超低频振动，这些振动会导致地球在之后的许多天里像钟声一样响起。 我们一直在努力改进地震仪，使其能够记录如此广泛的信号。 研究它们可以提供关于地球内部的许多信息。 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，地震和相关的现象也会引起地壳缓慢而渐进的变形。 为了检测这些变形，需要非常精确的传感器。 通常要寻找两种变形：地面相对于当地垂直线的位置发生非常微小的变化，称为“倾斜”;地面的伸长或压缩，称为“应变”。“这些并非无关，但由构造活动引起的信号类型通常非常小-以倾斜和应变的十亿分之一测量。 该奖项支持开发高灵敏度的光学检测方法和仪器，以测量由水泥固定在钻孔底部的外壳中的弹簧或弹簧悬挂的质量的运动。 光纤将激光向下发送到传感器外壳，并在光从连接到质量块的镜子反射后返回。 通过使用电子设备和位于钻孔外的小型计算机分析这种光，研究人员可以检测到与单个原子直径相当的质量运动，从而检测到地震相关活动引起的地面小地震震动和变形。随着研究人员对地震过程的了解越来越多，有一天对地震发生的地点和时间做出精确预测的机会就越大。该奖项的支持将允许制造和安装一个钻孔系统，该系统利用光纤干涉测量法在一个钻孔中提供：（a）宽频带垂直地震仪/重力仪，（B）宽频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。 该组合系统将能够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，使仪器寿命长，并能抵抗井下高温。该仪器将安装在Pinon Flat天文台现有的钻孔中，用于测试和与那里已经运行的地震和应变系统进行比较。 这一组合仪器有望取代独立地震仪、全球定位系统接收器、重力仪、倾斜仪和应变仪的多仪器观测。 预计地震观测将满足全球地震观测网台站目前的要求，而大地测量将提供比全球定位系统更低的噪音观测，观测周期短于数周。 目标应用可包括研究地壳变形的动力学，包括缓慢滑动事件、连续和偶发滑动以及已知会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岩浆和地下流体动力学的影响（例如，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.