Identifying and Modeling Complex Site Response Behavior

当地震波从深处传播到地表时，地球的近地表特性会改变地震波，从而影响社会。这个过程通常被称为场地反应，是导致特定位置地震危险的重要因素。正如在过去的地震中所观察到的那样，自由表面附近的慢速材料会影响短距离内的破坏模式。场地响应是近地表物质的物理性质和这些性质的空间分布的函数。不幸的是，在线性和非线性范围内的土壤行为的盲预测实验一直表明，预测的放大很少匹配观察到的放大。我们假设，现有的网站响应模型的性能不佳的是，标准的假设不足以代表网站响应行为的复杂性，在许多情况下。大多数场地响应模型依赖于横向均匀介质（SH 1D）中垂直传播S波的假设。在这项研究中，我们着手评估多个网站的弱和强的运动已被测量和三维（3D）土壤信息存在的现场响应。所选择的站点提供从简单到复杂的站点响应行为的序列。场地响应模型将包括通过3D空间可变和非线性介质的3D波传播。这项研究将测试是否有一个更复杂的网站响应模型可以解释的行为，观察到在这些网站。此外，我们将概述一种方法来识别和建模复杂的网站响应时需要。这项研究将集中在四个KiK网络网站。场地满足两个标准：（1）场地记录了2003年M8.3 Tokachi-Oki地震的大加速度（最大加速度从0.40到0.51 g），以及（2）场地套件包括那些对弱地面运动的SH 1D响应具有最佳、中等和最差拟合特征的场地（即，从简单到复杂的站点响应行为）。利用该数据集，我们将测试空间和本构模型预测复杂场地响应行为的准确性。简约原则要求数值模型的复杂程度取决于数据的要求。因此，我们将量化在不同复杂程度下可以实现的准确性，以便从业者可以就特定项目所需的空间数据范围和本构模型的复杂性做出明智的决定。我们将考虑从线弹性到超弹塑性的一系列本构模型。这项研究的学术价值在于挑战了S波通过横向恒定介质的一维垂直传播的标准假设，并为更复杂和更准确的现场响应模型奠定了基础。可用的计算能力不断增加，并接近模拟从源到站点的波传播的能力;然而，目前最常见的方法是独立地模拟非线性效应和3D效应。这项研究是将建模的这两个重要方面结合起来的第一步。这项工作的更广泛的影响包括指导内外的项目团队，特别侧重于本科工程人口在塔夫茨，并通过在线地质灾害数据库联盟@塔夫茨广泛传播现场数据的四个网站响应网站的不同复杂性。

The near-surface properties of the earth modify seismic waves as they propagate from depth to the surface where they are felt and effect society. This process is often called site response, and is an important factor that contributes to the seismic hazard at a specific location. As observed in past earthquakes, the slower materials near the free surface influence damage patterns over short distances. Site response is a function of both the physical properties of near surface materials and the spatial distribution of those properties. Unfortunately, blind prediction experiments both in the linear and nonlinear range for soil behavior have consistently shown that predicted amplifications rarely match the observed amplifications. We hypothesize that the poor performance of existing site response models is that the standard assumptions do not adequately represent the complexity of site response behavior in many cases. The majority of site response models rely on the assumption of vertically propagating S-waves through laterally homogeneous media (SH1D). In this research, we set out to evaluate site response at multiple sites where both weak and strong motions have been measured and three-dimensional (3D) soil information exists. The selected sites provide a sequence from simple to complex site response behavior. Site response models will include 3D wave propagation through a 3D spatially variable and nonlinear medium. This reserach will test whether or not a more complex site response model can explain the behavior that is observed at some of these sites. Further, we will outline a method to identify and model complex site response when needed.This research will focus on four KiK-net sites. The sites fulfill two criteria: (1) the sites recorded large accelerations from the 2003 M8.3 Tokachi-Oki earthquake (with maximum accelerations from 0.40 to 0.51 g), and (2) the suite of sites include those that are characteristic of the best, intermediate, and worst fit to the SH1D response for weak ground motions (i.e., simple to complex site response behavior). With this dataset we will test the accuracy of both spatial and constitutive models for predicting complex site response behavior. The principle of parsimony demands that numerical models be only as complex as the data require. Thus, we will quantify the accuracy that can be achieved at various levels of complexity so that practitioners can make informed decisions about the extent of spatial data and complexity of the constitutive model needed for a particular project. We will consider a sequence of constitutive models from linear-elastic to hyperelastic-plastic. The intellectual merit of the research is to challenge the standard assumptions of one-dimensional vertical propagation of S-waves through a laterally constant medium and lay the groundwork for more complex and more accurate site response models. The available computational power is continually increasing and is approaching the ability to model wave propagation from source to site; however, the most common approaches currently model nonlinear effects and 3D effects independently. This research is a first step toward combining these two important aspects of modeling. The broader impacts of this work include mentoring within and beyond the project team with specific focus on the undergraduate engineering population at Tufts, and the broad dissemination of in situ data for four site response sites of varying complexity with through the online Geohazards Database Consortium @ Tufts.