Implications of Explosion Generated Spall Models: Regional Seismic Signals
Abstract
The contribution of the spall source to the short period regional explosion seismogram is studied using new parametric models for the spallation seismic source derived from (2-D) axisymmetric nonlinear finite difference simulations for underground nuclear explosions. It is concluded that in high- velocity crustal structures spall may be a significant source of short period Lg and may significantly affect the Pg excitation. Regional phase excitation from a vertical point force and a horizontal tension crack are examined. A new general derivation for the equivalence between the two representations at low frequencies (horizontal wavelength>> spall depth) is given. Numerical calculations show that the vertical point force at the free surface above the spall is a good approximation in the short period bandwidth but degrades at high frequencies (horizontal wavelength < half the spall length). A smoothing operator is presented to account for the distributed finite nature of the spall. This operator represents a distributed spall disk with zero motion at the tip, and has an upward concave spall surface. Keywords: Seismic waveforms, Finite difference, Regional waveforms.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1990
- Accession Number
- ADA227273
Entities
People
- K. L. Mclaughlin
- S. M. Day
- T. G. Barker