EFFECTS OF OPEN GAPS ON PARTICLE-VELOCITY MEASUREMENTS

Joints and bedding planes are present in nearly all geologic media. Th ese discontinuities vary in the extent to which they are open and the material with which they are filled. The presence of such discontinuit ies affect the ground motions that result from the detonation of an ex plosive source. The effects of these discontinuities are especially im portant if it is desired to predict the size of the explosive source f rom measurements of ground motion - such as particle velocity or stres s. In this paper we present results from a series of model tests condu cted to investigate the effect of open gaps on the particle velocity t hat can be transmitted across them. Electromagnetic velocity gages wer e used to record particle velocities at several locations on either si de of an open gap of known width. The study was restricted to the tran smission of particle velocities normal to the gap and to the case wher e the gap was located in a region for which the stress was high but no t greatly above the elastic limit of the material. The experimental re sults were compared qualitatively to results obtained from WONDY - a o ne dimensional Lagrangian finite difference code. Although the tests w ere conducted in laboratory models, the results can be scaled to compa re to the full scale situation.