Modeling the Long-Period Basin Response in San Fernando and Los Angeles Regions During the 1994 Northridge Earthquake

模拟 1994 年北岭地震期间圣费尔南多和洛杉矶地区的长周期盆地响应

• 批准号: 9422238
• 负责人: Robert Graves
• 金额: $ 3.99万
• 依托单位: Woodward-Clyde Consultants
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-09-01 至 1997-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9422238&HistoricalAwards=false
• 关键词: Modeling; Long; Period; Basin; Response

9422238 Graves Objective The objective of the proposed work is to understand and quantify the effects that the San Fernando and Los Angeles sedimentary basins had on the long-period (1-10 sec) ground motion response during the Northridge earthquake, and to formulate recommendations for the inclusion of basin effects investigations in future seismic hazard analyses. Significance The Northridge earthquake and its aftershocks have produced the most comprehensive set of strong motion data ever recorded for a single earthquake sequence. These data allow for a wide range of research involving the analysis and modeling of earthquake source, path and site effects within the Los Angeles region. One important area of concern is to understand the effect that the deep sedimentary basins which underlie the San Fernando and Los Angeles regions had on the amplification and focusing of long-period (1-10 sec) seismic energy during this earthquake. Previous work has shown that wave propagation effects related to the geologic structure of the Los Angeles and San Fernando basins have a significant impact on the observed ground motions, particularly for periods longer than about 1 sec. and in many cases, these basin-induced effects dominate the ground motions in the period range 1-10 sec. During the Northridge earthquake, localized areas of intense ground shaking and associated damage were observed that cannot be explained by conventional attenuation relations (e.g., Santa Monica, I-10 freeway collapse). It is important to understand the cause of these phenomena and address their implications for engineering design, particularly for large structures (e.g., tall buildings, freeway bridges, base-isolated structures), which are most sensitive to long-period energy. Method and Anticipated Results This investigation involves the analysis of ground motion recordings of the Northridge earthquake and its aftershocks in order to systematically map out the observed basin effects within the San Fernando and Los Angeles regions. A key element of this analysis is the numerical modeling of these data using a 3D elastic finite-difference technique. The finite-difference approach is attractive because it allows flexibility in incorporating strongly heterogeneous velocity models, as well as using a finite, variable-slip source model. The goal of this project is to: (1) produce long-period (1-10 sec) time histories calculated on a fine spatial mesh throughout the San Fernando and Los Angeles regions; (2) display the results in map format, which will illustrate the spatial distribution of generated ground motions (e.g., wave field timeslices, distribution of peak velocity and duration of shaking) and the correlation of these motions with the subsurface geology; and (3) compare these results with those obtained using existing empirical attenuation relations, as well as the results calculated for 1D velocity models, in order to quantify the effects of the basin response for use in future seismic hazard analyses. ***

本研究的目的是了解和量化圣费尔南多和洛杉矶沉积盆地对北岭地震长周期（1-10秒）地震动响应的影响，并为在未来的地震危害分析中纳入盆地效应研究提出建议。北岭地震及其余震产生了一组最全面的强震数据，记录了单一地震序列。这些数据允许进行广泛的研究，包括对洛杉矶地区的震源、路径和地点影响的分析和建模。一个值得关注的重要领域是了解圣费尔南多和洛杉矶地区下方的深层沉积盆地在这次地震中对长周期（1-10秒）地震能量的放大和集中的影响。先前的研究表明，与洛杉矶和圣费尔南多盆地的地质结构有关的波传播效应对观测到的地面运动有重大影响，特别是在超过1秒的周期内。在许多情况下，这些盆地引起的效应在1-10秒的周期范围内主导着地面运动。观察到局部地区强烈的地面震动和相关的破坏，不能用传统的衰减关系来解释（例如，圣莫尼卡，I-10高速公路崩溃）。重要的是要了解这些现象的原因，并解决其对工程设计的影响，特别是对于大型结构（例如，高层建筑，高速公路桥梁，基础隔离结构），这是对长周期能量最敏感的。该研究包括对北岭地震及其余震的地面运动记录进行分析，以便系统地绘制出在圣费尔南多和洛杉矶地区观测到的盆地效应。该分析的一个关键要素是使用三维弹性有限差分技术对这些数据进行数值模拟。有限差分方法很有吸引力，因为它可以灵活地结合强非均质速度模型，以及使用有限的可变滑动源模型。该项目的目标是：(1)在整个圣费尔南多和洛杉矶地区的精细空间网格上计算出长周期（1-10秒）的时间历史；(2)将结果以地图的形式显示出来，以显示产生的地震动的空间分布（如波场时间片、峰值速度分布和震动持续时间）以及这些运动与地下地质的相关性；(3)将这些结果与利用现有经验衰减关系获得的结果以及一维速度模型计算的结果进行比较，以便量化盆地响应的影响，以便在未来的地震危害分析中使用。＊＊＊