Effect of Gaseous Products of Underground Chemical Explosions on Seismic Coupling

Abstract The effect of the amount of gaseous by‐products from small chemical explosions on seismic source signatures is examined. The explosions analyzed in this article were conducted using different types of explosives (ammonium nitrate–fuel oil and Composition B) as a part of the New England Damage Experiment (NEDE) in Barre, Vermont. These explosives have different densities, burn rates, and energy contents per unit mass, and upon detonation they produce different amounts and compositions of gaseous by‐products. The amount of gas products released during the detonation depends on the chemical composition of the explosives as well as on the presence of other compounds in and around the cavity that can vaporize or chemically decompose during the explosion (e.g., water). Analysis of the NEDE data suggests that the characteristics of the P spectra from these explosions depend on the amount of noncondensable gases released in the cavity during explosive detonation. The low‐frequency amplitudes of the explosion spectra show strong correlation with the amount of gas produced by the explosions, which can be explained by higher steady‐state pressure in the cavity resulting in a larger cavity and subsequently higher static value of the reduced displacement potential. Alternatively, the increase in low‐frequency amplitudes can be due to a longer duration of the source function caused by the late time damage from gas‐driven fracturing. The amplitudes in the high‐frequency band around the corner frequencies (overshoot amplitudes) show a relationship with the trinitrotoluene (TNT)‐equivalent yield and with the heat of the detonation. Thus, based on our dataset, the increase in the low‐frequency amplitudes with the corresponding decrease in overshoot parameter can be explained by the increase of the amount of cavity gas released during the detonation. Online Material: MP4 movies of NEDE1 and NEDE2 explosions.