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

地震仪对远距离地震和其他现象产生的微小地面运动很敏感。人们早就知道，在没有地震的情况下，这些仪器还会记录下背景‘嗡嗡声’，这是一种源自地球的低水平地震信号，能量每隔6-300秒循环一次。在海洋中移动的被称为“亚重力波”的宽波是大多数“嗡嗡声”的来源，当它们在海水中传播时，会对海底施加循环压力。海洋对海底的“强迫”和地球的地震“嗡嗡声”之间的这种一般关系是可以理解的，但有多少是沿着海洋的浅边缘产生的，而不是在深海盆地内产生的，为什么？本项目研究了“嗡嗡声”的源区(S)与大风暴通过之间的关系。它探索了海岸斜坡的形状是否会影响产生多少嗡嗡声的能量。为了完成这项工作，海底和大陆上的地震仪将被用来组合来自一系列仪器探测到的信号的信息，并指向海底强迫发生的位置。通过地震学家和海洋学家的合作，次重力波(IG)能级的空间变异性、海洋风暴对这种模式的影响、微震的产生和地球长期的“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。数值模型将被用来探索横跨大陆架的可能波浪行为的范围。将在太平洋西北部的近海地区研究风力驱动的海浪、IG波和海底之间的耦合。这项研究的结果将有助于表征海底IG噪声水平，将这种变异性与近岸IG波气候联系起来，并为未来地震和压力阵列的近海部署提供指导。提高对地球来源的理解？S哼唱可能有助于设计利用长周期地震噪声数据来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的地区，因为它已被记录为“嗡嗡声”的强大来源地区。研究生将在这项跨学科的研究中发挥重要作用，获得阵列处理技术的经验，如堆叠、波束形成和反投影。

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.