Analysis and modeling of the near-source seismic wavefield from small and large chemical explosions.

摘要

A series of controlled seismic experiments was performed in a limestone quarry in southern Germany to study the seismic effects of cylindrically shaped charges fired in both a half space (HS) and a quarter space (QS) geometry. Charge columns contained from 20-32 kg of explosives and were initiated from the bottom. The explosives formed cylinders 4 m (20 kg) and 5 m (32 kg) high and 90 mm in diameter at depths from 3-8 m. Prior to each of the larger explosions, small charges of 0.12 kg were fired at 4 m and 8 m depths in the same borehole. Seismograms were obtained from 23 three-component surface stations and up to 10 three-component borehole stations (6 m depth). For each experiment, stations were located on three linear profiles of 72 m length at different azimuths from the source and one semicircular profile at a constant range of 30 m. Wave propagation analysis indicates strong inhomogeneity across the test area as evidenced by a low velocity zone near the quarry face due to preconditioning by prior blasting, preferred propagation directions, and increased spallation of the surface influenced by a thin weathered layer in the limestone. Seismic signals from the smaller explosions were utilized as empirical models for the complex wave propagation. Linear superposition of the seismograms from the 0.12 kg charges interpolated between 4 and 8 m depth produced seismograms for use in deconvolving cylindrical charge signals.