Collaborative Research: The origin and propagation of shallow water microseisms: a multidisciplinary study at Yellowstone Lake

合作研究：浅水微震的起源和传播：黄石湖的多学科研究

• 批准号: 1760056
• 负责人: Robert Sohn
• 金额: $ 7.41万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-06-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1760056&HistoricalAwards=false
• 关键词: Collaborative; Research; origin; propagation; shallow

Microseisms are very small displacements (micrometers) of the Earth's solid surface that have been detected since that advent of seismometers, but the source of these vibrations was a mystery to scientists until about 60 years ago, when it began to become clear that they are largely generated by ocean waves. There are two main ways that ocean waves can generate microseism energy: 1) the interaction between waves traveling in different directions in the open ocean (secondary microseisms), and 2) the interaction of waves with the seafloor in shallow areas near the coast (primary microseisms). We presently have a good understanding of secondary microseisms, but the generation and propagation of primary microseisms is not well understood. Recently, it has been discovered that several large lakes around the world also produce microseism energy, including Yellowstone Lake in Yellowstone National Park. Yellowstone Lake provides a unique opportunity to study microseisms because, unlike the large oceans, it is relatively small and can be completely surrounded by seismic instruments, which gives us the opportunity to pinpoint the locations where microseisms are being generated and to study how they propagate into the surrounding regions. Our project will take advantage of the ongoing HD-YLAKE project, which deployed an array of seismometers on the floor of Yellowstone Lake, by supplementing those instruments with arrays of seismometers on the lake's perimeter and islands. In addition, we will also deploy instruments to simultaneously measure key atmospheric information (air temperature, pressure, wind speed, and wind direction) and the lake waves (amplitude, period, and direction) while the seismometers are recording. This combination of atmospheric, wave, and seismic data has never been collected in one place before, and it will provide an unprecedented opportunity to understand the processes that generate microseisms. Our results will have broad implications for the study of microseisms, and ultimately, we want to develop the ability to use these naturally occurring seismic waves to image the Earth's structure. This is an exciting possibility in Yellowstone Lake, because it hosts active hydrothermal systems that are believed to create large gas pockets in the lake floor sediments, and the microseism propagation velocity should be very sensitive to the presence of gas. As a broader impact, the investigators will work with Yellowstone Park educators to make their results accessible to the wider public through their exhibits.Technical Summary: It has recently been found that many lakes generate observable microseisms at periods near 1 s. Observations from land-based seismometers deployed near lakes show that the microseisms propagate as short-period Rayleigh waves (Rg), often with prograde particle motion because of the low velocity of lake sediments. However, it is unknown if the source process is linear, corresponding to primary ocean microseisms, or non-linear, corresponding to secondary ocean microseisms, or both. It is also unknown whether the source regions are predominantly in the open water or near the shoreline, and how the microseismic wavefield evolves as it crosses the shoreline. Yellowstone Lake is an excellent natural laboratory for understanding shallow water microseisms because (1) there are no potentially confounding swells from distant storms, as there are in the oceans, (2) the source region is geographically small and can essentially be surrounded with seismometers, and (3) the Yellowstone Lake microseisms are a regular, repeatable phenomenon associated with diurnal wind variation during the summer and fall. An understanding of the source mechanism of Yellowstone Lake microseisms will likely be applicable to other shallow water regions around the world and could lead to improved imaging of very shallow Earth structure. The proposed work involves a monthlong deployment of (1) 40 three-component, autonomous, 5-Hz geophones around the perimeter of Yellowstone Lake and on islands within the lake, (2) four weather stations collocated with selected geophones, and (3) two wave-height recorders in the northern portion of the Yellowstone Lake. The deployment is planned for the summer of 2018 so that it can overlap with the ongoing, NSF-funded, HDYLAKE experiment, which deployed an array of 10 lake-bottom seismometers around an active hydrothermal site. The PIs and a graduate student will analyze the interdisciplinary data set in an effort to determine the origin and generation mechanism of the short-period (~1 sec) microseisms that were recently observed to originate from Yellowstone Lake during periods of open water.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.

自从地震仪出现以来，微观主义是地球固体表面的非常小的位移（微米），但是直到大约60年前，这些振动的来源对科学家来说都是一个谜由海浪产生。海浪有两种主要方式可以产生微观主义能量：1）在开阔的海洋中以不同方向行驶的波之间的相互作用（次级微作用），以及2）波浪与海岸附近浅层地区的海浪相互作用（主要微震）。目前，我们对二级微作用有很好的了解，但是原发性微观主义的产生和传播尚不清楚。 最近，已经发现世界各地的几个大湖也产生了微群落的能源，包括黄石国家公园的黄石湖。黄石湖提供了研究微作用的独特机会周围地区。我们的项目将利用正在进行的HD-ylake项目，该项目通过在湖外围和岛屿上用一系列地震仪的阵列补充这些乐器，在黄石湖地板上部署了一系列地震仪。此外，我们还将部署工具以同时测量关键的大气信息（空气温度，压力，风速和风向）以及湖泊波（振幅，周期和方向），同时记录地震仪。大气，波浪和地震数据的这种结合以前从未在一个地方收集过，它将提供前所未有的机会来了解产生微观主义的过程。我们的结果将对微观主义的研究具有广泛的影响，最终，我们希望发展使用这些天然发生的地震波来对地球结构进行成像的能力。这是黄石湖的一种令人兴奋的可能性，因为它具有主动的热液系统，据信它们会在湖面沉积物中产生大型气口，而微质主义传播速度应该对存在气体非常敏感。作为更广泛的影响，调查人员将与黄石公园教育者合作，通过其展览使更广泛的公众可以访问其结果。技术摘要：最近发现，许多湖泊在1秒钟附近产生可观察到的微观主义。 从湖泊附近部署的陆基地震仪的观察结果表明，微质主义作为短期雷利波（RG）传播，通常由于湖泊沉积物的速度低而采用前体颗粒运动。但是，尚不清楚源过程是线性的，对应于原发性海洋微作用或非线性，对应于次级海洋微作用，或两者兼而对应。源区域是否主要在开放水域还是在海岸线附近，以及微丝膜波场在越过海岸线时如何发展。黄石湖是理解浅水微作用的绝佳自然实验室，因为（1）没有遥远的风暴中的膨胀，就像海洋中的那样，（2）源区域在地理上很小，基本上可以被地震米包围，而是可以包围（3）黄石湖微作用是夏季和秋季与昼夜风变化相关的常规，可重复的现象。对黄石湖微质主义的源机制的理解可能适用于世界上其他浅水区域，并可能改善对非常浅的地球结构的成像。拟议的工作涉及（1）40个三个组件的部署，在黄石湖周围和湖泊内的岛屿周围和岛屿周围的自主，5-Hz的地球管，（2）四个与选定的地球座相处的天气站，以及（3）黄石湖北部的两个波浪高录制员。该部署计划在2018年夏季进行，以便它可以与正在进行的NSF资助的Hdylake实验重叠，该实验部署了10个湖底地震仪，周围是活跃的热液场所。 PIS和研究生将分析跨学科数据集，以确定最近观察到的短期（〜1 sec）微作用的起源和发电机制，这些机制最近被观察到源自敞开的水。反映了NSF的法定任务，并使用基金会的知识分子优点和更广泛的影响审查标准来评估值得支持。