Abstract

Explosions near the Earth’s 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) for above/belowground emplacements. We report analyses 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 and HOB scaled by yield. We find that displacement of the initial P wave and the integral of the positive overpressure (impulse) are diagnostic of W and HOB with minimal scatter. An empirical model describing the dependence of seismic and air‐blast measurements 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. Our signal models are used to invert seismic and overpressure measurements for W 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 measurement types allows us to largely break this trade‐off and better constrain W and HOB. However, both models lack resolution of HOB for aboveground explosions.

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