Modeling of Block Motions due to a Buried Explosion. Excitation of Acoustic Waves by Seismic Sources

Abstract : A study conclusions include: (1) Qualitative effects of block motions in axisymmetric geometry on the outgoing radiation field are usefully described by an analytical model if the boundary condition across them slipping interface is linear. Comparison between analytical and numerical results shows that our numerical treatment of imperfectly bonded joints in a rock mass is correct and accurate; (2) Quantitative agreement between numerical simulations and field observations is achieved for a rate independent dry friction boundary condition, with a kinetic friction coefficient of 0.77; and (3) In axisymmetric geometry, an equivalent seismic source which accounts for block motion contains both dipole and octuopole terms. Evaluation of these contributions to the elastodynamic radiation field, for both linear and nonlinear boundary conditions shows that this equivalent source is a very poor radiator at long periods, and cannot lead to surface wave reversals. Also reported is an investigation of acoustic coupling of seismic waves. We have validated the results of previous simulations of this phenomenon which used the San Fernando earthquake, reviewed the literature to determine the range of source parameters to be expected for earthquakes of magnitude of approx. 4.0, and are proceeding with the modeling of near source ground motion associated with a well-recorded (M sub L = 4.1) aftershock of the Oroiville sequence.