Near-field Rayleigh waves from surface explosions

The low-frequency components of the near-field ground motions produced by surface explosions are investigated and evidence is presented which suggests that much of this motion can be accounted for by the Rayleigh waves induced by the airblast loading acting on the surface exterior to the region of strong nonlinear response (i.e., the crater). Scaling laws are derived for this component of the motion which indicate that the amplitude of the Rayleigh wave source function is expected to be directly proportional to yield and independent of site geology at low frequencies and to scale as yield to the one-third power and increase with the near-surface shear wave velocity at high frequencies. Finally, an unusual arrival recorded interior to a hexagonal array of surface explosions is analyzed and shown to be consistent with Rayieigh waves converging on the center from an exterior, axisymmetric, surface-ring load which may correlate physically with the multi-burst spall closure for this event