The Loma Prieta earthquake, ground motion, and damage in Oakland, Treasure Island, and San Francisco
The Loma Prieta earthquake, ground motion, and damage in Oakland, Treasure Island, and San Francisco
复制标题
洛马普列塔地震、地面震动以及奥克兰、金银岛和旧金山的破坏
DOI：
10.1785/bssa0810052019
复制
发表时间：
1991
影响因子：
3
通讯作者：
A. G. Brady
中科院分区：
文献类型：
--
作者：
T. Hanks;A. G. Brady
这项研究的基础是洛马普里塔地震（1989 年 10 月 18 日；M = 7.0）的加速度、速度和位移波形，这些地震发生在旧金山的两个岩石地点、耶尔巴布埃纳岛的一个岩石地点、金银岛的一个人工填充地点以及奥克兰的三个地点，这些地点下面是厚厚的固结不良的更新世沉积物。三个岩石地点的波形显示出很强的一致性，奥克兰的三个沉积地点也是如此。岩石地点的强烈运动持续时间非常短暂，表明这种规模的地震的震源持续时间异常短，而奥克兰的记录则显示出由于地点地质而产生的强烈放大效应。金银岛的 S 波群与奥克兰的记录相位一致，但幅度有所减小，直到大约 15 秒加速，显然表明液化开始了。所有七个记录都清楚地显示，剪切波第一运动与主震辐射模式的预期相反，并且峰值振幅大于距该震级地震这些距离（95±3公里）的地点的预期。
虽然这些地面运动记录与附近地区相关损坏模式之间的关联已被地震学和工程观察者轻松而热切地接受，但我们在量化甚至明确这种关系方面遇到了一些困难。奥克兰的三个记录来自于赛普拉斯街高架桥倒塌形成近等边三角形的地点，主要由长周期共振（≃ 1 1/2 秒周期）主导，该共振与结构的固有频率和横向运动（2.5 Hz）或余震研究中观察到的高频放大频带相去甚远。这种差异的频谱比仲裁器使其更加混乱。旧金山-奥克兰海湾大桥东湾桥的失败不能归因于奥克兰和耶尔巴布埃纳岛桥台的相对位移，但导致失败的海湾大桥的运动仍然未知。金银岛的加速步骤存在不寻常的强运动加速度图处理问题，并且建模表明速度和位移波形受到滤波操作对加速步骤的寄生响应的污染。各种巧合表明，金银岛加速度图最有可能是滨海区填充区域的强震动替代品，该区域没有可用的主震记录，但不良地面、不良建筑和真正强烈的地面运动对滨海区损害的相对影响永远不会以任何定量方式得知。所有这一切的主要教训是，除非齐心协力对地震期间可能失效的地面和结构进行检测，否则我们对强烈地震动和地震破坏之间非常复杂的关系的理解总体上仍然是初级的、不精确的和模糊的。
The basis of this study is the acceleration, velocity, and displacement wave-forms of the Loma Prieta earthquake (18 October 1989; M = 7.0) at two rock sites in San Francisco, a rock site on Yerba Buena Island, an artificial-fill site on Treasure Island, and three sites in Oakland underlain by thick sections of poorly consolidated Pleistocene sediments. The waveforms at the three rock sites display a strong coherence, as do the three sedimentary sites in Oakland. The duration of strong motion at the rock sites is very brief, suggestive of an unusually short source duration for an earthquake of this size, while the records in Oakland show strong amplification effects due to site geology. The S-wave group at Treasure Island is phase coherent with the Oakland records, but at somewhat diminished amplitudes, until the steps in acceleration at approximately 15 sec, apparently signaling the onset of liquefaction. All seven records clearly show shear-wave first motion opposite to that expected for the mainshock radiation pattern and peak amplitudes greater than expected for sites at these distances (95 ± 3 km) from an earthquake of this magnitude.
While the association between these ground motion records and related damage patterns in nearby areas has been easily and eagerly accepted by seismological and engineering observers of them, we have had some difficulty in making such relationships quantitative or even just clear. The three Oakland records, from sites that form a nearly equilateral triangle about the Cypress Street viaduct collapse, are dominated by a long-period resonance (≃ 1 1/2-sec period) far removed from the natural frequency of the structure to transverse motion (2.5 Hz) or from high-frequency amplification bands observed in aftershock studies. A spectral ratio arbiter of this discrepancy confuses it further. The failure of the East Bay crossing of the San Francisco-Oakland Bay Bridge cannot be attributed to relative displacements of the abutments in Oakland and Yerba Buena Island, but the motions of the Bay Bridge causing failure remain unknown. The steps in acceleration at Treasure Island present unusual strong-motion accelerogram processing problems, and modeling suggests that the velocity and displacement waveforms are contaminated by a spurious response of the filtering operations to the acceleration steps. A variety of coincidences suggests that the Treasure island accelerogram is the most likely strong-motion surrogate for the filled areas of the Marina District, for which no mainshock records are available, but the relative contributions of bad ground, poor construction and truly strong ground motion to damage in the Marina District will never by known in any quantitative way. The principal lesson of all of this is that until a concerted effort is mounted to instrument ground and structures that are likely to fail during earthquakes, our understanding of the very complex relationships between strong ground motion and earthquake damage will, in general, remain rudimentary, imprecise, and vague.