Long-Period Strong Ground Motion Prediction Using the Ambient Seismic Field

我们将使用环境地震场来预测长周期强地面运动中的线性波传播效应。环境场由扩散地震波组成，可以用来提取地球对集中震源的响应，包括相对放大。由于频率带宽、激励深度和激励背后的力系统的限制，这与地震类似。环境场反应代表了一种地面运动预测的新工具，本提案寻求在两个地震多发地区：加利福尼亚和日本开发和利用这种工具。我们选择这些地点的理由是，已经存在的地面运动模拟显示，在这两个国家的大城市，如洛杉矶和东京，有很强的盆地效应。在这两种情况下，还有充足的连续地震数据可用于环境场分析，以及中等地震的分布，以验证该方法。日本被微地震噪声源所包围，仪器密集，地震频率是加州的5倍，可能是世界上测试和开发环境噪声用于地面运动预测的最佳地点。地震学最重要的任务之一是预测大地震的震动强度。这为工程师提供了设计抗震结构所需的信息，也为决策者提供了制定有效应对策略所需的信息。目前地面运动预测的实践主要基于经验，即基于过去地震的地面运动记录。它没有充分利用我们所知道的控制地震的因素。盆地放大是大城市中心地震动预测误差的主要来源。盆地捕获并放大了地震波，从而增加了城市对地震的脆弱性。在现有的衰减关系中，盆地效应常常被忽略，或者充其量只是粗略地加以近似。这意味着迫切需要地面运动模拟来了解建在盆地上的城市的地震危害，如洛杉矶、西雅图、东京和大阪。这样的模拟正在进行中，但如果要使它们有用，就必须证明它们是正确的。我们的研究开创了一种测试和改进这种计算的新方法。拟议中的研究是国际性的，这项研究的一个重要的更广泛的影响将是扩大和深化美国和日本地震科学家之间的合作关系。该提案将资助地震学女研究生Marine Denolle的博士研究。开发这种方法将对验证地面运动模拟产生更广泛的影响，并使它们能够为地震工程师所接受。这将对长期结构（桥梁和高层建筑）的设计和改造产生特别重要的影响。这项工作是由地球物理计划和国际科学与工程办公室共同资助的。

We will use the ambient seismic field to predict linear wave propagation effects in strong ground motion at long periods. The ambient field consists of diffuse seismic waves that can be used to extract the response, including relative amplification, of the earth to a concentrated source. Due to limitations in the frequency bandwidth, the depth of excitation, and the force system behind the excitation, this is similar to an earthquake. The ambient-field response represents a new tool for ground motion prediction, and this proposal seeks to develop and exploit this tool in two earthquake-prone regions: California and Japan. Our rationale for choosing these locations is that there already exist ground motion simulations that show strong basin effects for large cities, such as Los Angeles and Tokyo, in both countries. There are also ample continuous seismic data available for ambient-field analysis in both cases, as well as a distribution of moderate earthquakes against which to validate the method. Japan - surrounded as it is by sources of micro-seismic noise, instrumented with dense networks, and subject to ~5 times the rate of earthquakes as California - may be the best place in the world to test and develop ambient noise for ground motion prediction.One of the most important tasks of seismology is to predict the intensity of shaking in large earthquakes. This provides the information engineers need in order to design earthquake-resistant structures, and policymakers need in order to develop effective response strategies. Current practice in ground motion prediction is based primarily on experience, that is, on records of ground motion in past earthquakes. It fails to take advantage of all that we know about the factors that control earthquake shaking. Basin amplification is a key source of discrepancies in ground motion prediction for large urban centers. Basins trap and amplify earthquake waves and thereby increase the vulnerability of cities to earthquakes. Basin effects are often neglected, or at best are crudely approximated, in existing attenuation relations. This means that ground motion simulations are urgently needed to understand urban earthquake hazards for cities built on basins, such as LA, Seattle, Tokyo, and Osaka. Such simulations are being carried out, but if they are to be useful, they must be shown to be correct. Our research pioneers a new way to test, and to improve, such calculations.The proposed research is international, and an important broader impact of this research will be to widen and deepen the collaborative ties between earthquake scientists in the US and Japan. The proposal will fund the Ph.D. research of Marine Denolle, a female graduate student in seismology. Developing this method would have the broader impact of validating ground motion simulations and rendering them acceptable for use for earthquake engineers. This should have a particularly important impact in the design and retrofitting of long-period structures (bridges and high-rises).This work is co-funded by the Geophysics Program and the Office of International Science and Engineering.