DOE OSTI2011
Motion along joints and fractures in the rock has been proposed as one of the sources of near-source shear wave generation, and demonstrating the validity of this hypothesis is a focal scientific objective of the source physics experimental campaign in the Climax Stock granitic outcrop. A modeling effort has been undertaken by LLNL to complement the experimental campaign, and over the long term provide a validated computation capability for the nuclear explosion monitoring community. The approach involves performing the near-field nonlinear modeling with hydrodynamic codes (e.g., GEODYN, GEODYN-L), and the far-field seismic propagation with an elastic wave propagation code (e.g., WPP). the codes will be coupled together to provide a comprehensive source-to-sensor modeling capability. The technical approach involves pre-test predictions of each of the SPE experiments using their state of the art modeling capabilities, followed by code improvements to alleviate deficiencies identified in the pre-test predictions. This spiral development cycle wherein simulations are used to guide experimental design and the data from the experiment used to improve the models is the most effective approach to enable a transition from the descriptive phenomenological models in current use to the predictive, hybrid physics models needed for a science-based modeling capability for nuclear explosion monitoring. The objective of this report is to describe initial results of non-linear motion predictions of the first two SPE shots in the Climax Stock: a 220-lb shot at a depth of 180 ft (SPE No.1), and a 2570-lb shot at a depth of 150 ft (SPE No.2). The simulations were performed using the LLNL ensemble granite model, a model developed to match velocity and displacement attenuation from HARDHAT, PILE DRIVER, and SHOAL, as well as Russian and French nuclear test data in granitic rocks. This model represents the state of the art modeling capabilities as they existed when the SPE campaign was launched in 2010, and the simulation results presented here will establish a baseline that will be used for gauging progress as planned modeling improvements are implemented during the remainder of the SPE program. The initial simulations were performed under 2D axisymmetric conditions assuming the geologic medium to be a homogeneous half space. However, logging data obtained from the emplacement hole reveal two major faults that intersect the borehole at two different depth intervals (NSTec report, 2011) and four major joint sets. To evaluate the effect of these discrete structures on the wave forms generated they have performed 2D and 3D analysis with a Lagrangian hydrocode, GEODYN-L that shares the same material models with GEODYN but can explicitly take joints and fault into consideration. They discuss results obtained using these two different approaches in this report.