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Toward a Stochastic Interpretation of Shear Motion Generation of Underground Explosions in Jointed Rock

April 11, 2018 @ 11:00 am - 12:00 pm

We have performed 3D simulations of underground explosions conductedrecently in granitic outcrop as part of the Source Physics Experiment (SPE)campaign. The main goal of these simulations is to understand the nature of theshear motions recorded in the near field under condition of uncertainties in a)the geological characterization of the joints, such as density, orientation andpersistency and b) the geomechanical material properties, such as, to name afew, friction angle, bulk sonic speed, poroelasticity etc. The approach isprobabilistic; joints are depicted using a Boolean stochastic representation ofinclusions conditional to observations and their probability density functionsinferred from borehole data. Then, using a novel continuum approach, joints andfaults are painted into the continuum host material, granite. To insure thefidelity of the painted joints we have conducted a sensitivity study continuumvs. discrete representation of joints. Simulating wave propagation inheterogeneous discontinuous rock mass is a highly non-linear problem anduncertainty propagation via intrusive methods is practically forbidden.Therefore, using a series of nested Monte Carlo simulations, we have exploredand propagated both the geological and the geomechanical uncertaintyparameters. We have probabilistically shown that significant shear motions canbe generated by sliding on the joints caused by spherical wave propagation.Polarity of the shear motion may change during unloading when the stress statemay favor joint sliding on a different joint set. Although this study focuseson understanding shear wave generation in the near field, the overall goal ofour investigation is to understand the far field seismic signatures associatedwith shear waves generated in the immediate vicinity of an undergroundexplosion. Therefore, we have abstracted the near field behavior into a probabilisticsource-zone model which is used in the far field wave propagation.


About the Speaker: Souheil M Ezzedine

Souheil is an applied mathematician and statistician within WCI and GS at Lawrence Livermore National Laboratory. He is a computational physicist withinAEED/PLS. Souheil is versatile in deterministic and stochastic numerical methods.He is an alumnus of École Nationale Supérieure des Mines de Paris, UC Berkeleyand UC Davis and has 10 years of consulting experience. While at LLNL, Souheilhas been a technical staff on multi-disciplinary projects: Yucca Mountainnuclear storage, underground coal gasification, geological carbonsequestration, infrastructure vulnerabilities, probabilistic detection ofburied structures, asteroids deflection and their impact on earth, LLNLnear-field liaison for SPE and LYNM containment source venture deputy. Souheil supportsa variety of DOE, DOD and DHS funded projects.



Host: Tim Kneafsey



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