Comprehensive Understanding of Near-field Acceleration Recordings by a New HHT Analysis

CMS0085272标题：“通过新的HHTanalysis全面了解近场加速度记录”PI：R.Zhang研究所：科罗拉多矿业学院摘要：近场地面加速度记录揭示了许多与中远场完全不同的振动/波特征。其中包括记录开始时的低频脉冲波信号和高能量分布。它们主要在以下两个方面非常有用：(1)作为模拟地震波运动和/或解释地球上地震现象的输出，它们可以帮助解决震源机制、方向性影响和土壤动力非线性等地震学问题。(2)作为岩土工程和结构工程系统的输入，它们可用于计算非线性动力响应，从而评价系统的抗震性能。这种分析可以根据从中场到远场地震动记录获得的知识来量化地震对设计的各种工程系统的影响。然而，在1999年土耳其Kocaeli和台湾集集地震之前，世界上只有8个7级以上地震的地面运动记录，距离断层不到20公里。数据的缺乏限制了对近场运动的量化性质及其对工程系统影响的研究。此外，传统的方法(例如，傅立叶或基于傅里叶的小波分析)从地面运动记录中提供失真或间接的信息。这可能会在一定程度上误导随后使用地面运动数据来解决上述地震和工程问题。本研究试图使用一种新发展的希尔伯特-黄变换(HHT)来综合分析柯凯里地震和集集地震的近场加速度记录。具体而言，建议的研究集中在以下方面：(1)从原始数据中分离出未失真的低频脉冲波信号，并根据其峰值和持续时间给出它们的简单度量；(2)提供运动的时频地震能量分布的准确表示；揭示了两次地震的近场和远场记录、不同断层方位观测点的近场运动以及两次地震的近场运动与美国大地震(如1992年兰德斯地震)之间的共性和差异。已经成立了一个多学科研究小组来执行拟议的项目，成员包括PI、科罗拉多州丹佛市USGS的一名高级结构工程研究员(Erdal Safak)和一名地震学家(Stephen Hartzell)。这项研究的结果将通过互联网在与这两次地震有关的指定网页上发布。地震学家和工程师将能够将这些结果用于他们在相关研究前沿的进一步研究和应用。这一研究不仅有助于提高我们对震源的认识，而且也将提高对地震运动对各种结构的破坏潜力的认识，从而提高当代结构抗震设计的水平。

CMS0085272Title: "Comprehensive understanding of near-field acceleration recordings by a new HHTanalysis"PI: R. ZhangInstitution: Colorado School of MinesAbstract:Near-field ground acceleration recordings have revealed many vibration/wave characteristics that are uniquely different from the medium- to far-field ones. These include, among others, the low-frequency pulse-like wave signals and high-energy distribution in the beginning of the recordings. They are very useful primarily in the following two aspects:(1) As the output in modeling earthquake wave motions and/or explaining earthquake phenomena in the earth, they can help solve such seismological issues as source mechanism, directivity influence, and soil dynamic non-linearity. (2) As the input to geotechnical and structural engineering systems, they can be used to compute dynamic nonlinear responses and thus to evaluate seismic performance of systems. This analysis can quantify earthquake impact on various engineering systems designed on the basis of knowledge obtained form medium- to far-field ground motion records. However, before the 1999 Kocaeli (Turkey) and Chi-Chi (Taiwan) earthquakes, there existed only 8 ground motion recordings worldwide for earthquakes greater than a magnitude 7 and at a distance of less than 20 kilometers from the fault. The lack of data has restricted studies on the quantitative nature of near-field motion and its impact on engineering systems. In addition, conventional approaches (e.g., Fourier or Fourier-based wavelet analysis) supply either distorted or indirect information from the ground motion recordings. This might mislead, to a certain extent, the consequent use of the ground motion data for solving the aforementioned seismological and engineering issues. This study seeks to use a newly developed Hilbert-Huang Transform (HHT) to comprehensively analyze the near-field acceleration recordings of the Kocaeli and Chi-Chi earthquakes. In particular, the proposed study focuses on the following subjects:(1) singling out the undistorted low-frequency pulse-like wave signals from the original data and presenting a simple measure of them in terms of their peak and duration; (2) providing an accurate representation of time-frequency seismic energy distribution of the motion; and(3) revealing the commonality and difference in terms of vibration/wave characteristics of the motion among the near- and far-field recordings of each of the two earthquakes, among the near-field motions at observation sites with different orientations to the fault, and among the near-field motions of the two earthquakes compared with large-magnitude US earthquakes (e.g., 1992 Landers earthquake). A multi-disciplinary research team has been formed to perform the proposed project, consisting of the PI, and a senior structural engineering researcher (Erdal Safak) and a seismologist (Stephen Hartzell) at USGS at Denver, CO. The results from this study will be disseminated through the Internet at designated web pages related to these two earthquakes. Seismologists and engineers will be able to use the results for their further studies and applications in pertinent research frontiers. This study will not only help advance our knowledge of the earthquake source, but it will also improve the understanding of the damage potential of earthquake motion on various structures and thus enhance the contemporary seismic-resistance structural design.