Effects of Fracture Anisotropy and the Free Surface on Secondary Seismic Radiation from Small Shallow Underground Explosions
Abstract
We have developed a micromechanical damage mechanics that is capable of modeling the nucleation, growth, and interaction of fracture damage at the high loading rates found in the non-linear source region of underground nuclear explosions. This model predicts the generation of strong S wave radiation in the non-linear source region whenever spherical symmetry is broken. Examples of phenomena that break spherical symmetry include tectonic pre-stress, preferred orientation of pre-existing fractures (anisotropic rock fabric), and the lithostatic stress gradient. We have recently extended the damage model to allow an anisotropic distribution of initial damage in a three-dimensional half-space and used it to model the asymmetric fracture pattern and seismic radiation observed for a chemical explosion in a granite quarry in Barre, Vermont. To first order effect of fracture anisotropy is to make the moment tensor of the explosion look like a tensile crack aligned in the rift direction of the rock fabric. Many nuclear tests and then NPE chemical explosion have similar moment tensors.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 06, 2018
- Accession Number
- AD1068295
Entities
People
- Charles G. Sammis
Organizations
- University of Southern California