Severe Ground Motions

Stanford University, Stanford CA

Investigators

Abstract

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.