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

CMS 0085272标题：“通过新的HHT分析全面了解近场加速度记录“PI：R。张机构：科罗拉多矿业学院摘要：近场地面加速度记录揭示了许多振动/波的特性，是独特的不同，从介质到远场的。 其中包括低频脉冲状波信号和记录开始时的高能量分布。 它们主要有两个方面的作用：（1）作为模拟地震波运动和解释地球中地震现象的输出，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)作为岩土和结构工程系统的输入，它们可以用来计算动力非线性响应，从而评估系统的抗震性能。 这种分析可以量化地震对各种工程系统的影响，这些工程系统是根据从中远场地震动记录中获得的知识设计的。然而，在1999年科贾埃利（土耳其）和集集（台湾）地震之前，全世界只有8个地震记录超过7级，距离断层不到20公里。 数据的缺乏限制了近场运动的定量性质及其对工程系统的影响的研究。 此外，常规方法（例如，傅立叶或基于傅立叶的小波分析）从地面运动记录中提供失真或间接的信息。 这在一定程度上可能会误导地震动数据在解决上述地震学和工程问题中的后续使用。 本研究试图使用一个新发展的希尔伯特-黄变换（HHT），全面分析近场加速度记录的科贾埃利和集集地震。 本文的研究重点是：（1）从原始资料中提取出无畸变的低频脉冲波信号，并给出其峰值和持续时间的简单度量;（2）提供运动时频地震能量分布的精确表示;（3）揭示了近场和远场运动在振动/波动特征方面的共性和差异。两次地震中的每一次的现场记录，在具有与断层不同取向的观测点处的近场运动中，以及在与大震级美国地震相比的两次地震的近场运动中（例如，1992年兰德斯地震。 一个多学科的研究小组已经形成，以执行拟议的项目，包括PI，和高级结构工程研究员（Erdal Safak）和地震学家（Stephen Hartzell）在美国地质勘探局在丹佛，CO。从这项研究的结果将通过互联网传播在指定的网页与这两次地震。 地震学家和工程师将能够利用其结果进行进一步的研究和应用在相关的研究前沿。 这项研究不仅将有助于提高我们对震源的认识，而且还将提高对地震运动对各种结构的破坏潜力的理解，从而提高当代抗震结构设计。

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.