The Li Ka Shing Women in Science Distinguished Speaker Series
Speaker: Prof. Barbara Romanowicz (Earth and Planetary Science, UC-Berkeley; the Director of Berkeley Seismological Laboratory; a member of the Academy of Science, USA)
Location: The lecture hall on the first floor, Marine Building
Date: 14:30-15:30pm,October 19th, 2009
The observation of continuously excited free oscillations of the Earth, in the absence of earthquakes, was first made by Japanese scientists in 1998. Since then, attention has focused on elucidating the physical mechanism responsible for them. The mechanism must be shallow, as fundamental modes appear to be preferentially excited and the observed amplitudes show seasonal variability. We have developed an array-based method to detect and locate sources of the hum, using a propagating wave approach, the dispersive properties of Rayleigh waves and data from two large aperture arrays of very long period seismometers, in California and in Japan. We have shown that, for each array, there is a well defined preferential direction, which is stable over one season but changes significantly from winter to summer. The fluctuations as a function of time of the maximum stack amplitudes are correlated across the two arrays and point to the northern Pacific ocean in the northern hemisphere winter and the southern Oceans in the summer, correlating with the temporal fluctuations in the distribution of maximum wave height on the global scale (Figure 1). We have inferred that the background oscillations originate primarily in the oceans, and are caused by a non-linear coupling mechanism involving the atmosphere (winds), the oceans (infragravity waves) and the seafloor (Rhie and Romanowicz, 2004). Further analysis of several particularly large North Pacific storms indicates that a given ocean storm can produce a series of relatively weak seismic sources, and that the coupling occurs most likely when the ocean waves reach the continental shelf, by interaction with the complex ocean floor topography. We showed in particular that the Rayleigh waves produced can be followed deep inside the north American continent. We also discuss observations of infragravity waves on broadband ocean bottom seismometers located off-shore California, and their relationship to wind waves and seismic noise, showing that the ocean/solid earth coupling occurs near the coast. This has recently been confirmed by observations on the large and dense USArray broadband array.
1998年日本的科学家首次观测到在没有地震的情况下地球连续激发的自由振荡。从那时起，人们开始研究引起这种现象的物理机制。该机制的源应该是浅的，因为基本模式波被优先激发而且观测到的波的幅度随季节而变化。我们发展了基于阵列的方法来对地球的“hum”进行检测和定位，使用了波传播的方法和瑞利波的频散特性并利用了在加州和日本的两个超长周期、大孔径的地震阵列记录到的数据。我们发现对每个阵列都有一个特别的方向，该方向在一个季节里是稳定的，但从冬天到夏天变化巨大。这两个阵列的最大叠加幅度随时间的起伏具有相关性，并在冬天指向北半球的北太平洋，在夏天指向南边的海洋，这与全球的最大浪高分布的时间变化相对应。我们推断这种背景振荡起源于海洋，并且是由不同圈层包括大气层（风）、海洋（亚重力波）和海底的非线性耦合机制而引起（Rhie and Romanowicz, Nature, 2004）。对几个特别大的北太平风暴的进一步分析表明，一个海洋风暴可以产生一系列相对较弱的地震震源，当海洋波到达大陆架时通过与复杂海底地形的相互作用最有可能发生耦合。我们的研究特别表明这种耦合产生的瑞利波可以进入北美大陆的深部。我们也讨论了在加州近海布设的宽频带海底地震仪观测到的重力波以及它们与风波和地震噪音的关系，发现海洋/陆地的耦合发生在近海。这个发现最近被大而密集的宽频带美国地震阵列的观测所证实。
The Li Ka Shing Foundation
The Li Ka Shing Foundation Women in Science Distinguished Speaker Series at UC Berkeley was established to create academic exchanges in science and foster collaboration between women scientists in the United State and Mainland China.
About the Li Ka Shing Foundation
? ? ? ?For almost three decades, the Li Ka Shing Foundation has sought to enhance the impact of its philanthropy through two strategic objectives- to nurture a culture of giving and to foster creativity, constructive engagement, and sustainability. Education and medicine form the key areas of work for the Li Ka Shing Foundation. Shantou University is a cornerstone project of the Li Ka Shing Foundation. It is uniquely the only public university that is supported by private funds and its mission is to engineer education reform and to promote global learning in China. The Li Ka Shing Foundation and other charities established by Mr. Li Ka Shing have supported grants, sponsorships, and commitments of over HK$10.9 billion.
? ? ? ?The Li Ka Shing Foundation Women in Science Distinguished Speaker Series at UC Berkeley was established to create academic exchanges in science and foster collaboration between women scientists in the United States and Mainland China.
最后更新 (2012-07-13 10:33)