Accession Number:

ADA243956

Title:

Spectral Studies of the Elastic Wave Radiation from Appalachian Earthquakes and Explosions-Explosion Source Spectra Modeling Using Blaster's Logs

Descriptive Note:

Technical rept.

Corporate Author:

VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG DEPT OF GEOSCIENCES

Report Date:

1991-09-01

Pagination or Media Count:

51.0

Abstract:

Objectives of this study are to model the observed spectra of seismic radiation from large industrial explosions using information obtained from blasters logs, and to compare the explosion spectra with those of small earthquakes occurring in the same source region. The data set consists of digital waveforms from four mining explosions 200,000 lbs of explosives each and two earthquakes M 3.5,4.0 in eastern kentucky. Data were recorded on a short-period regional network at distances ranging from 180 to 400 km and have good signal-to-noise ratios at frequencies from 0.5 to 10 Hz. The explosion amplitude spectra were found to differ markedly from those of earthquakes, by exhibiting strong time-independent amplitude modulations. This spectra modulation is shown to be directly attributable to the explosive charge geometry and detonation sequence employed, and is independent of source-station path and recording site. Modeling the explosion source spectra shows that the major contributor to the modulated character of the spectra are amplitude minima at frequencies related to the total duration of the explosion sequence. Another important effect is spectral reinforcement at low frequencies e.g., 5 Hz due to the comparatively long delay 0.2 sec between the firing of individual rows of explosives. These features dominate both Pg and Lg amplitude spectra at frequencies less than 7 Hz. Accurate modeling of the observed spectra at frequencies greater than a few Hertz requires the azimuth of the recording site be taken into account. Spectra at higher frequencies become sensitive to random variations in the firing times of any of the various sub-explosions.

Subject Categories:

  • Seismology
  • Seismic Detection and Detectors

Distribution Statement:

APPROVED FOR PUBLIC RELEASE