Tele-infrasonic studies of hard-rock mining explosions

Area of Science:

• Geophysics
• Atmospheric Science
• Acoustics

Background:

• Infrasound monitoring relies on accurate atmospheric profiles for modeling.
• Explosions at Minnesota iron mines provide a controlled source for studying infrasound propagation.
• The Lac-du-Bonnet infrasound station (IS-10) is strategically located for these observations.

Purpose of the Study:

• To evaluate the accuracy of atmospheric models for infrasound propagation.
• To analyze the impact of explosion characteristics and atmospheric conditions on infrasound observations.
• To compare different atmospheric datasets for infrasound travel time prediction.

Main Methods:

• Analysis of infrasonic data from 2003 explosions at Minnesota iron mines.
• Comparison of observed infrasound arrivals with predictions from atmospheric models.
• Utilizing Mass Spectrometer Incoherent Scatter/Horizontal Wind Model (MSIS/HWM) and Naval Research Laboratory Ground to Space (NRL-G2S) datasets.
• Employing parabolic equation (PE) modeling and the Sutherland/Bass model.

Main Results:

• Observed infrasound arrivals had frequencies of 0.5–5 Hz, with a dominant frequency of 2 Hz and short durations.
• Explosion size did not correlate with infrasound observability.
• The NRL-G2S dataset yielded more accurate travel time predictions than MSIS/HWM.
• PE modeling with NRL-G2S suggested energy loss at higher frequencies (around 4 Hz).
• The Sutherland/Bass model applied to NRL-G2S predicted amplitudes were too small to be observed.

Conclusions:

• Atmospheric conditions and noise levels significantly impact infrasound detection.
• The NRL-G2S dataset shows promise for improving infrasound travel time predictions.
• Further refinement of atmospheric models and propagation models is needed for accurate amplitude prediction.