Low Frequency Characterization of Coherency Functions for Spatially Varying Earthquake Ground Motion

摘要：CMS-9710953， Ronald Harichandran, Michigan State u。自20世纪70年代末以来，近距离地震仪阵列的观测表明，在典型大型工程结构的尺寸范围内，不同位置测量的地震地面加速度有显著差异。这导致了对空间变化地震地面运动的建模以及确定其对大型结构（如桥梁、管道和水坝）的地震反应的影响的相当大的关注。对各种结构体系的研究表明，包括空间变化的地震地震动的影响往往会增加临界响应，因此不考虑这种现象的大型结构设计可能是不安全的。表征空间变化的地震地面运动的一个关键组成部分是相干函数，它描述了在不同空间位置记录的加速度之间的不相干性。不同的研究者对相干函数提出了不同的函数形式，但对这些不同形式如何影响计算响应的研究很少。此外，由于一些常用模型的低频相干变化差异很大，因此解决矛盾并为工程师提供指导至关重要。本研究计划的目标是利用高分辨率最大熵谱估计方法和长时程加速度记录来解决这些矛盾，使用来自墨西哥谷，台湾SMART-1阵列，日本千叶阵列和美国北岭地震的记录。本项目是与墨西哥国立自治大学（UNAM）的合作研究计划，涉及美国工程师，一个墨西哥工程师，一个墨西哥地震学家。

ABSTRACT: CMS-9710953, Ronald Harichandran, Michigan State U. Observations from closely-spaced seismograph arrays since the late 1970's have shown that earthquake ground accelerograms measured at different locations within the dimensions of typical large engineered structures are significantly different. This has resulted in considerable attention being given to the modeling of spatially varying earthquake ground motions, and on determining its effect on the seismic response of large structures such as bridges, pipelines, and dams. Studies on various structural systems have shown that including the effect of spatially varying earthquake ground motions often increases critical responses, and hence large structures designed without consideration for this phenomenon may be unsafe. A key component in the characterization of spatially varying earthquake ground motions is the coherency function, which describes the incoherence between accelerations recorded at different spatial locations. Different functional forms have been proposed by different investigators for coherency functions, but studies on how these different forms affect the computed responses have been few. Also, since the low- frequency variation of coherency is significantly different among some of the commonly used models, it is critical to resolve contradictions and provide guidance to engineers. The objective of this research program is to use the high- resolution maximum entropy spectral estimation method and long-duration accelerogram records to resolve these contradictions, using records from the Valley of Mexico, the SMART-1 array in Taiwan, the Chiba array in Japan, and the Northridge earthquake in the U. S. This project is a cooperative research program with the Universidad Nacional Autonoma de Mexico (UNAM), involving a joint collaboration between a U. S. engineer, a Mexican engineer, and a Mexican seismologist.