Earthquake on the Hussar low-frequency experiment

Kevin W. Hall, Gary F. Margrave

On the last day of acquisition on the Hussar low-frequency line, a magnitude 6.3 earthquake occurred offshore of Vancouver Island, British Columbia, Canada. The low-frequency seismic line included 10 Hz 3-C geophones at 10 meter station spacing, VectorSeis 3-C accelerometers at 10 meter spacing, 4.5 Hz geophones at 20 meter spacing, a partial line of high-sensitivity 10 Hz geophones at 10 Hz spacing and Nanometrics compact seismometers at 200 meter spacing. Earthquake arrivals were recorded during acquisition of source line 6, which was a Failing vibe running two 1-100 Hz low-dwell sweeps per vibe point. The earthquake was successfully recorded by all sensors that were part of the low-frequency experiment, at a distance of about 1050 kilometers from the epicenter. The earthquake arrivals have an apparent velocity of about 4500 m/s across the 4.5 km seismic line. Inverse filtering of the 10 Hz and 4.5 Hz geophone data to correct for geophone response at low frequencies is shown to be succesfull, based on visual inspection, at enhancing data with frequencies of less than one Hertz.