Philip E. Harben

Partitioning of Seismoacoustic Energy and Estimation of Yield and Height‐of‐Burst/Depth‐of‐Burial for Near‐Surface Explosions

Explosions near the Earths surface excite both seismic ground motions and atmospheric overpressure. The energy transferred to the ground and atmosphere from a near-surface explosion depends on yield (W) as well as the height-of-burst/ depth-of-burial(HOB/DOB)forabove/belowgroundemplacements.Wereportanalyses of seismic and overpressure motions from the Humble Redwood series of low-yield, near-surface chemical explosions with the aim of developing quantitative models of energy partitioning and a methodology to estimate W and HOB/DOB. The effects of yield, HOB, and range on amplitudes can be cast into separable functions of range andHOBscaledbyyield.WefindthatdisplacementoftheinitialPwaveandtheintegral of the positive overpressure (impulse) are diagnostic of W and HOB with minimal scat- ter. An empirical model describing the dependence of seismic and air-blast measure- ments on W, HOB/DOB, and range is determined and model parameters are found by regression. We find seismic amplitudes for explosions of a given yield emplaced at or above the surface are reduced by a factor of 3 relative to fully contained explosions below ground. Air-blast overpressure is reduced more dramatically, with impulse reduced by a factor of 100 for deeply buried explosions relative to surface blasts. Oursignalmodelsare usedtoinvertseismicandoverpressure measurementsforW and HOB and we find good agreement (W errors <30%, HOB within meters) with ground- truth values for four noncircular validation tests. Although there is a trade-off between W and HOB for a single seismic or overpressure measurement, the use of both meas- urement types allows us tolargelybreak this trade-off and better constrainW and HOB. However, both models lack resolution of HOB for aboveground explosions.

Seismic noise cancellation in a geothermal field

High background seismic noise due to process machinery in production oil or geothermal fields can present a major problem for active seismic studies such as reflection and refraction surveys and passive seismic studies such as microearthquake monitoring. The general noise suppression problem is a difficult one since process noise may be due to a large number of sources distributed over a large region. In some situations, one or a few sources may dominate the noise field locally, presenting an opportunity for noise suppression by cancellation. In this note we describe an application of adaptive noise cancellation (Widrow, et al., 1975) in which we attempt to suppress noise recorded at a primary monitoring site using reference noise recorded at a major nearby noise source.

Seismic Models for Near‐Surface Explosion Yield Estimation in Alluvium and Sedimentary RockSeismic Models for Near‐Surface Explosion Yield Estimation in Alluvium and Sedimentary Rock

Author(s): Templeton, DC; Rodgers, AJ; Ford, SR; Harben, PE; Ramirez, AL; Foxall, W; Reinke, RE | Abstract:

Acoustic source calculations for nuclear bursts

Research has been conducted on the source term for long‐range underwater propagation of signals from nuclear explosions in and above the ocean, in support of CTB monitoring objectives. A suite of source‐region simulations is reviewed to study the variation of wave properties and source‐region energy partition as a function of height or depth of burst. The multistep calculation combines LLNL’s CALE hydrodynamics code in the strong shock region with NRL’s weak shock code, NPE, at intermediate ranges. The source term calculations are intended as a starter field for long‐range linear propagation models to obtain signature estimates at normal observational ranges. Calculations are presented to examine the effect of sea ice below an air burst on acoustic coupling into the water column. The ice was modeled as a continuous elastic layer 5‐m thick at the water surface, and the source as a 1‐Kt explosion 50 m above the ice. Calculations with and without the ice layer predict a moderate, but noticeable reduction in coupled acoustic energy in signals observed at the 10 000‐m range. [Work performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W‐7405‐ENG‐48.]