Bottom seismometer observation of airgun signals at Lopez Island

First arrival compressional wave signals from an airgun source, as detected by a variety of seismometers in a shallow bay, are remarkably uniform. However, minor variations in wavelet appearance imply some combination of the instrument response and coupling to the bottom. Signal spectra show typically a spectral peak at 12 Hz and an envelope very similar to that expected from an airgun source. Those instruments with a decoupled geophone package have spectra most like the theoretical spectrum but spectra for the other instruments are not significantly different. Little variation exists in spectra between tripod-mounted and inverted-pendulum OBS configurations for the low amplitude P-waves observed here. The signal source is the principal influence on the resulting spectra rather than OBS configuration or bottom coupling.