A Rotating Tiltmeter for Marine Geodesy: Development and Testing at Axial Seamount on the Ocean Observatories Initiative Cabled Array

测量地球构造板块运动引起的地面变形对于旨在了解火山和地震的科学研究很重要。倾斜仪是一种测量地面倾斜或坡度变化的仪器，例如，当火山在喷发前膨胀时，或者当引起地震的应力抬升地球的一部分相对于另一部分时。设计倾斜仪的一个挑战是，由于传感器的不稳定，测量结果往往会随时间漂移，这限制了它们测量缓慢变化的倾斜信号的能力。该项目将开发一种新型的倾斜仪，通过根据地球引力校准传感器来校正仪器漂移，地球引力在地球上的任何一点都可以被认为是恒定的。倾斜仪将部署在东北太平洋活火山Axial Semount的一个实时有线海底观测站上。这是一个具有重大科学价值的地点；这座火山在20年内喷发了三次。它也是一个用其他方法测量倾斜度的地方，这允许对新仪器进行验证。这台仪器收集的数据将向公众和其他科学家开放。未来，倾斜仪可能有助于研究，试图了解导致俯冲带大地震或导致危险火山喷发的地质过程。该项目将培养一名研究生，并为本科生提供在海上帮助部署该仪器的实地机会。海底形变的大地测量对于了解大洋板块边界的地球动力学过程至关重要，但具有相当大的挑战性。该项目将采用一种新的方法来创建短基线倾斜仪。该倾斜仪是基于高分辨率三分量石英晶体加速度计。如果将加速度计放置在与海底耦合的稳定平台上，则加速度计水平通道倾角的变化将导致测量的加速度随时间变化，但传感器的漂移也会随时间变化。校正传感器漂移的水平通道的方法是通过将每个水平通道旋转(或翻转)成垂直的短时间间隔来进行周期性校准，以测量重力加速度g。由于g具有在任何位置不变的高精度，因此g的测量在连续旋转之间的变化可归因于传感器漂移。然后，这种漂移测量可用于校正每个水平加速度计通道，以获得校准之间的真实倾斜变化的时间序列。由此得到的倾斜仪将具有独特的特点：高动态范围(它不能超出刻度)、高精度(~几个nrad)和校准后良好的长期稳定性(10微rad)。至少一年的数据将在轴海山上的海洋天文台倡议有线天文台收集。

Measurements of ground deformation due to the motion of the Earth's tectonic plates are important for scientific research aimed at understanding volcanoes and earthquakes. Tiltmeters are instruments that measure changes in the tilt or slope of the ground that can occur for example, when a volcano inflates prior to an eruption or when the stresses that cause earthquakes lift up one part of the earth relative to another. A challenge with designing tiltmeters is that the measurements tend to drift with time due to instability in the sensors ¡V this limits their ability to measure tilt signals that are changing slowly. This project will develop a new type of tiltmeter that will correct for instrument drift by calibrating the sensor against the Earth's gravitational force, which can be considered constant at any point on the Earth. The tiltmeter will be deployed on a real-time cabled seafloor observatory at Axial Seamount, an active volcano in the Northeast Pacific Ocean. This is a site of significant scientific interest; the volcano has erupted three times in 20 years. It is also a site where tilt is being measured by other methods which allows validation of the new instrument. The data collected by this instrument will be made available to the public and other scientists. In the future, the tiltmeter may contribute to studies that seek to understand the geological processes that lead to great subduction zone earthquakes or that cause hazardous volcanic eruptions. The project will train a graduate student and provide field opportunities for undergraduates to help deploy the instrument at sea.Geodetic measurements of seafloor deformation are essential to understand geodynamic processes at oceanic plate boundaries but are quite challenging. The project will employ a novel approach to creating a short-baseline tiltmeter. The tiltmeter is based on a high-resolution three-component quartz crystal accelerometer. If the accelerometer is deployed on a stable platform that is coupled to the seafloor, changes in tilt of the horizontal channels of the accelerometer will lead to changes in the measured accelerations with time but so will the drift of the sensors. The approach to correcting the horizontal channels for sensor drift is to conduct a periodic calibration by rotating (or "flipping") each horizontal channel into the vertical for a short interval to measure the acceleration of gravity, g. Since g is to a high degree of accuracy invariant at any location, changes in the measurement of g between successive rotations can be attributed to sensor drift. This measurement of drift can then be used to correct each horizontal accelerometer channel to obtain a time series of true tilt changes between calibrations. The resulting tiltmeter will have unique characteristics ¡V a high-dynamic range (it cannot go off scale), high precision (~ a few nrads) and good long-term stability after calibration (10 micro rads). At least a year of data will be collected at the Ocean Observatories Initiative cabled observatory on Axial Seamount.