| Popis: |
Simultaneous infrasonic and seismic observations of meteor shock waves have been recorded at a collocated array in southwestern Ontario, Canada. Analysis of signals from seven events that exhibited acoustic-seismic coupling (representing 0.6% of the meteor flux detected using other systems) suggests signifi- cant filtering and amplitude enhancement indicative of a frequency-dependent acous- tic transfer function. The acoustic response at the site possesses the properties of an ∼10 Hz high-pass filter on incident shock waves, with ground motions up to an order of magnitude larger than theoretical predictions. In terms of energy, the air-to-ground energy coupling efficiency is measured at 1:3 � 0:8% above this cutoff. Overall cou- pling efficiencies, however, are much lower (between 0.0007% and 0.071%) as the dominant frequencies of the incident shock waves (typically 0.1-10 Hz) are weak or nonexistent in the seismic signals. Such strong frequency-dependent effects suggest that, without detailed knowledge of the site and its influences on the subsequent ground motion, transformation of seismic data to produce pseudopressure data for the purposes of quantitative source-energy estimation may be unreliable for seismom- eters located within thick overburden. |
