Severe Ground Motions

该项目的目标是提高工程师和科学家处理危及生命的、最严重的地面运动的准确性和有效性；这些运动的定义是那些可以引起高度非线性动力响应的运动，因此即使是那些经过现代抗震设计的建筑和结构也会受到破坏。目前确定结构安全的方法受到限制，因为无法预测当地面震动达到这些破坏性水平时会是什么样子。基于一种有效的新的(依赖于结构的)地面运动严重程度的标量测量，将对真实和真实合成加速度记录的套件进行排名，并确定最严重的以进行深入研究，以了解这些记录为什么以及如何与较良性的记录不同。方向性诱发的脉冲可能是靠近大断层地点的某些结构的一种这样的现象。这些结果将导致联合工程和地球科学工具的项目发展，以评估强烈运动的危险。这些工具将包括一种新的概率地震危险性分析程序，该程序利用现代执业工程师对其特定结构的某些线性和非线性动态特性的知识，然后产生特定的威胁测量，以便更准确地预测结构受到这些罕见的、严重的地面运动攻击时的需求。一个主要项目产品是动态破裂建模功能，它允许在大地震的非常近的区域模拟地面运动。由此，我们更好地了解了控制震源各方面行为的因素，主要是上升时间，这些因素对控制强烈地震动的程度和性质是很重要的。我们的模型是相对于它们产生记录样本的能力进行测试的，这些记录样本准确地捕获了早先发现的在结构中产生严重影响的属性。因此，该项目需要工程学和地球科学家之间非同寻常的互动。

The objectives of this project are to improve the accuracy and effectiveness of the way both engineers and scientists address the life-threatening, most severe ground motions; these are defined as those motions that can induce highly nonlinear dynamic response and hence damage even those building and structures that have undergone modern aseismic design. Current means of structural safety determination are limited by an inability to anticipate what the ground shaking will look like when it reaches these damaging levels. Based on an effective new (structure-dependent) scalar measure of ground motion severity, suites of real and samples of realistic synthetic accelerograms will be ranked and the most severe identified for study in depth to learn why and how these records differ from the more benign. Directivity-induced pulses can be one such phenomenon for certain structures at sites close to large faults.These results will lead to project development of joint engineering and earth science tools for the assessment of the hazard of severe motions. These tools will include a new probabilistic seismic hazard analysis procedure that takes advantage of the modern practicing engineer's knowledge of certain linear and nonlinear dynamic properties of his specific structure to then produce a particular measure of the threat that far more accurately predicts the demands on the structure when it is assaulted by these rare, severe ground motions.A major project product is a dynamic rupture modeling capability that allows simulations of ground motion in the very near field of large earthquakes. From this, we gain a better understanding of the factors that control behavior of aspects of the earthquake source, principally the rise time, that are important in controlling the level and character of severe ground motion. Our models are tested relative to their ability to produce samples of records that accurately capture the properties found earlier to produce severe effects in structures. Thus the project requires an unusual degree of interaction between engineering and earth scientists.