Explosion Source Model Development in Support of Seismic Monitoring Technologies: Apparent Explosion Moment and Prospects for Moment-Based Yield Estimation
Abstract
This paper reports on research activities for the third and final year of a project to develop new explosion source models that include the effects of source medium damage, a form of which is deep-seated, shock-induced tensile failure identified in our previous studies. In general, damage will contribute volumetric, compensated linear vector dipole (CLVD), and double-couple (DC) sources of seismic radiation. Our past work has studied the effects of a CLVD source on Rayleigh wave radiation and its impact on the performance of mb-Ms discrimination. Part I of this paper shifts attention to the volumetric contribution that source medium damage makes. In the model, there are two possible volumetric sources: (1) the traditional source associated with direct effects of explosions creating a cavity with volume V and (2) the damage source due to non-linear free-surface interactions and shock-wave rebound causing abrupt changes of elastic moduli and dilating the source medium with volume U due to bulking and shear dilatancy. The CLVD represents a non-volumetric, deviatoric source component of damage. K is a source parameter measuring the steady-state strength MCLVD of the CLVD with respect to MI, the isotropic moment. Moment tensor inversion results for NTS explosions show that K steadily decreases with yield, approaching values near 1.0 for highest yield shots. A K value of 1.0 implies MCLVD = 0 and, by inference, small U. Our hypothesis is that the force of spall slapdown is great enough at high yields to crush the tuff matrix, reducing U while V remains intact. Slapdown at low yields is not great enough to do so, leaving both V and U unaffected. We tested the hypothesis by comparing measurements of MI with estimates of "classical" moment based on scaling relationships of V and velocity models for Pahute Mesa, including the effects of coupling above the water table.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2010
- Accession Number
- ADA569493
Entities
People
- Howard J. Patton
Organizations
- Los Alamos National Laboratory