Omnipulse test results
Donald C. Lawton, Malcolm B. Bertram
A nine-component walkaway noise spread (32 geophones at 2 m intervals) was recorded with the Omnipulse TM source and 3-component geophones, to a maximum source receiver offset of 510 m. Matched source and receiver component data had the highest coherent energy level, with refractions, multiple refractions and surface waves being the major events recorded. Far-field P and S headwaves were found to have velocities of 3200 m/s and 1350 m/s respectively. Dispersive Rayleigh and Love waves were recorded, with group velocities less than 300 m/s and dominant frequencies of about 8 Hz. Love waves, generated with the SH source were particularly high in amplitude.
Post-acquisition array forming from the raw data showed a decrease in the relative amplitude and bandwidth of the surface wave energy. However, stacking resulted in severe phase distortion of these events.
Refraction analysis showed short-wavelength P-wave and S-wave statics of 5 ms and 15 ms over 4 m respectively, and a 5 degree standard deviation in apparent directivity.