Seismic Ground Motion from Free-Field and Underburied Explosive Sources
SYSTEMS SCIENCE AND SOFTWARE LA JOLLA CA
Pagination or Media Count:
Small-scale laboratory experiments were conducted and analyzed to study the effect of the proximity of the free surface on the seismic ground motions. Two classes of experiments were done. In one the charges were far from the free-surface and the free-field displacement-time histories were measured. In the second class the charges were near the surface and were either fully contained or formed a crater. The charges were 0.25 g of PETN in concrete cylinders, 120 cm in diameter and 33 to 60 cm thick. In all experiments displacements were measured 30.5 cm directly below the charges. The experiments produced consistent and repeatable data. A striking feature of the ground motions for the near surface experiments is a large long-period negative pulse which is present whether or not cratering occured. The results were studied by comparing to numerical simulations of the experiments using a Lagrangian finite difference program and published properties of the concrete and PETN. The calculations are in good agreement with the laboratory data, providing verification of both the constitutive models and the methods.