Investigation of Long-Period Ground Motion in the NorthridgeEarthquake of January 17, 1994.

9413273伊万1994年1月17日的北岭地震产生了一组可能被证明是从地震中获得的最有价值的强震数据。这些数据包括有记录以来最大的水平地面运动。与这些大型地面运动相关的破坏是有据可查的。在一些近场加速度记录中，特别是Sylmar站，有证据表明地面运动中存在显著的长周期位移脉冲。这种运动的存在最近引起了人们的极大关注，因为它涉及到基础隔震和高层结构的设计。这些结构特别容易受到大输入位移的影响。人们认识到有必要更好地了解这种长周期运动的性质，并最终能够对其发生进行建模和预测。目前用于处理强震数据的常规技术往往会从记录的加速度记录中去除或扭曲长周期信息。然而，根据美国国家科学基金会最近的一项探索拨款，已经开发出了在加速图中恢复大部分长周期信息的技术。这是通过非传统的基线校正和信号处理来实现的，其基础是对地面运动的物理和记录仪器的性质有了更好的理解。这些技术已经在兰德斯地震的地面运动中得到了验证。这项研究计划的目标是将最近开发的数据处理技术应用于北岭地震的一套地震记录。其最终目的是为结构设计提供一个可用于描述地震运动的长周期内容的准则的基础。这次探索性调查涉及以下问题：1.这类逆冲地震的长周期(位移)地震动的性质是什么？2.它如何随距离震中的距离和相对于断裂带的方位而变化。3.长周期内容(峰值位移)与短周期内容(峰值加速度)有何关系？4.对未来此类或其他类型的事件可作何概括？5.观测到的长周期地面运动与结构破坏之间是否存在相关性？这项研究基于从加州矿产和地质部和美国地质调查局获得的数字数据。***

9413273 Iwan The Northridge earthquake of January 17, 1994 yielded what may prove to be the most valuable set of strong motion data ever obtained from an earthquake. These data include the largest horizontal ground motion ever recorded. The damage associated with these large ground motions is well documented. In some of the near-field accelerograms, particularly the Sylmar station, there is evidence of a significant long period displacement pulse in the ground motion. The existence of such motion has recently been the subject of great concern as it relates to the design of base isolated and high-rise structures. These structures are particularly susceptible to large input displacements. There is a recognized need to better understand the nature of this long period motion and, ultimately, to be able to model and predict is occurrence. Present routine techniques for the processing of strong motion data tend to remove or distort the long-period information from recorded accelerograms. However, under a recent NSF exploratory grant, techniques have been developed to recover much of the long-period information in accelerograms. This is accomplished by nontraditional baseline correction and signal processing that is based on an improved understanding of the physics of the ground motion and the nature of the recording instruments. The techniques have been verified for ground motions from the Landers earthquake. The goal of this research program is to apply the recently developed data processing techniques to a suite of earthquake records from the Northridge earthquake. The ultimate goal is to provide a basis for guidelines that may be used to characterize the long-period content of earthquake motion for structural design. This exploratory investigation addresses the following questions: 1. What is the nature of the long period (displacement) content of ground motion from this type of thrust earthquake? 2. How does this vary with distance from th e epicenter and orientation with respect to the fault plain. 3. How is the long-period content (peak displacement) related to the short-period content (peak acceleration)? 4. What generalizations can be made to future events of this, or another, type? 5. Is there a correlation between the observed long-period ground motion and structural damage? The research is based on digital data obtained from the California Division of Mines and Geology and the U.S. Geological Survey. ***