Collaborative Research: Characterizing sources of infragravity waves and the earth's hum using data from the Cascadia Amphibious Array

合作研究：利用卡斯卡迪亚两栖阵列的数据来表征次重力波和地球嗡嗡声的来源

• 批准号: 1538276
• 负责人: Barbara Romanowicz
• 金额: $ 22.76万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-15 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1538276&HistoricalAwards=false
• 关键词: Collaborative; Research; Characterizing; sources; infragravity

Seismometers are sensitive to tiny ground motions generated by distant earthquakes and other phenomena. As has long been known, in the absence of earthquakes, these instruments also record a background 'hum', a low level seismic signal originating in the earth that has energy cycling every 6-300 seconds. Broad waves called "infragravity waves" moving through the ocean are the source of most of the 'hum', imparting cyclic pressure on the seafloor as they travel through the seawater. This general relation between ocean 'forcing' on the seafloor and Earth's seismic 'hum' is understood, but how much is generated along the shallow margins of the ocean versus within the deep ocean basins, and why? This project investigates the relationship between the source region(s) of the 'hum' and the passage of major storms. It explores whether the shape of the coastal slopes influences how much hum energy is produced. In order to accomplish the work, seismometers both on the seafloor and on the continent will be used to combine information from the signals detected across the array of instruments, and point toward the location where the seafloor forcing occurred.Through a collaboration between seismologists and oceanographers, the spatial variability of infragravity wave (IG) energy levels, the influence of ocean storms on that pattern, and the generation of microseisms and Earth's long period "hum" will all be documented. Broadband seismic and pressure spectra from the Cascadia amphibious array will be analyzed. Numerical models will be employed to explore the range of possible wave behaviors across the continental shelf. The coupling between wind-driven ocean waves, IG waves and the seafloor will be studied in a near-coastal region of the Pacific Northwest. The results of this study will contribute to the characterization of IG noise levels on the ocean floor, link this variability to the near shore IG wave climate, and provide guidance for future off-shore deployments of seismic and pressure arrays. Improved understanding of the sources of Earth?s hum may help design approaches to using long period seismic noise data for the study of deep earth structure. The west coast of North America is uniquely suited for this purpose as it is has been documented as a strong source region for the "hum". A graduate student will play a significant role in this cross-disciplinary research, obtaining experience in array processing techniques such as stacking, beamforming, and back projection.

地震计对远距离地震和其他现象产生的微小地面运动很敏感。众所周知，在没有地震的情况下，这些仪器也会记录背景“嗡嗡声”，这是一种源自地球的低水平地震信号，每6-300秒进行一次能量循环。被称为“亚重力波”的宽波在海洋中移动，是大多数“嗡嗡声”的来源，当它们在海水中移动时，会对海底施加周期性压力。海洋对海底的“作用力”和地球地震的“嗡嗡声”之间的一般关系是可以理解的，但是有多少是沿着海洋的浅边缘沿着产生的，而不是在深海盆地内产生的，为什么？这个项目调查了“嗡嗡声”的来源区域与主要风暴通过之间的关系。它探讨了沿海斜坡的形状是否会影响产生多少嗡嗡声能量。为了完成这项工作，将使用海底和大陆上的地震仪来联合收割机从仪器阵列检测到的信号中收集信息，并指向海底强迫发生的位置。通过地震学家和海洋学家之间的合作，研究了亚重力波（IG）能量水平的空间变化、海洋风暴对该模式的影响、而产生的微震和地球的长周期“嗡嗡声”都将被记录下来。 将分析卡斯卡迪亚两栖阵列的宽带地震和压力谱。将采用数值模型来探索横跨大陆架的可能的波浪行为的范围。将在太平洋西北部的近海岸区域研究风驱动的海浪、IG波和海底之间的耦合。 本研究的结果将有助于描述海底IG噪声水平的特征，将这种变化与近海岸IG波气候联系起来，并为未来在海岸部署地震和压力阵列提供指导。更好地了解地球的起源？这一结果有助于设计利用长周期地震噪声数据研究地球深部结构的方法。北美西海岸是唯一适合这一目的，因为它已被记录为一个强大的来源地区的“嗡嗡声”。研究生将在这项跨学科的研究中发挥重要作用，获得阵列处理技术，如堆叠，波束形成和反投影的经验。