HR: 0800h
AN: S11B-0164    [Abstracts]
TI: Time-Dependent Source Moment Tensors of Chemical Explosions With Various Source Configurations
AU: * Yang, X
EM: xyang@lanl.gov
AF: Los Alamos National Laboratory, EES-11, MS D408, Los Alamos, NM 87544 United States
AU: Bonner, J L
EM: bonner@westongeophysical.com
AF: Weston Geophysical Corporation, 4000 S. Medford, Suite 10W, Lufkin, TX 75901 United States
AB: We have developed time-dependent source moment tensors for nine chemical explosions detonated in a dedicated source-characterization field experiment. These explosions have different sizes, geometries, depths of burial and containment conditions. Two of the explosions also failed an adjacent vertical free face and resulted in horizontal material cast. These moment tensors provide insight into the source characteristics of these explosions, particularly the mechanisms of shear-wave generation from explosive sources. We employed a frequency-domain linear-inversion technique to obtain the moment tensors for these explosions. A detailed velocity model derived from refraction and surface-wave data was used. We also used surface-wave data to infer the medium attenuation required for the inversion. Near-source (< 700 m) broadband data were used in the inversion. The source moment tensors of all explosions are dominated by the isotropic component regardless of different source configurations. The time histories of the partially contained and uncontained explosions are more oscillatory than those of the contained explosions, possibly indicating the involvement of the explosion-free-surface interaction. The explosions that involved material cast have more complicated moment-tensor time histories. In addition, their moment tensors show an enhanced low-frequency (1-6 Hz) signal in the off-diagonal components, probably resulted from the material cast. Although the amplitude of the off-diagonal components is only a small fraction of the amplitude of the isotropic component, synthetic-seismogram calculation shows that it can generate shear waves of much larger amplitudes. This illustrates that although the deviatoric component of the moment tensor for an explosive source may be small compared with the isotropic component, it can be an important shear-wave generator.
DE: 7215 Earthquake source observations (1240)
DE: 7219 Seismic monitoring and test-ban treaty verification
SC: Seismology [S]
MN: Fall Meeting 2005