Severe Ground Motions

该项目的目标是提高工程师和科学家应对危及生命的最严重地面运动的准确性和有效性；这些被定义为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物和结构也会受到破坏。目前确定结构安全的手段是有限的，因为无法预测当它达到这些破坏性水平时地面震动会是什么样子。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的组合进行排名，并确定最严重的加速度进行深入研究，以了解这些记录与较良性的记录不同的原因和方式。对于靠近大断层的某些结构，方向性诱发脉冲可能就是这样一种现象。这些结果将导致工程和地球科学联合工具的项目开发，以评估剧烈运动的危害。这些工具将包括一个新的概率地震危害分析程序，该程序利用现代实践工程师对其特定结构的某些线性和非线性动力特性的知识，然后产生一个特定的威胁测量，更准确地预测当这些罕见的，严重的地面运动袭击时对结构的要求。一个主要的项目产品是动态破裂建模能力，可以模拟大地震近场的地面运动。由此，我们可以更好地了解控制震源各方面行为的因素，主要是上升时间，这对控制剧烈地面运动的水平和特征很重要。我们的模型是经过测试的，相对于它们产生记录样本的能力，这些记录样本准确地捕获了先前发现的对结构产生严重影响的特性。因此，该项目需要工程和地球科学家之间不同寻常的相互作用。

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.