Shear wave resonances in sediments on the deep sea floor [poster]

Abstract

Shear wave resonances at frequencies between about 0.1 and 10Hz are a ubiquitous feature of ambient noise and controlled source seismic data acquired on sedimented sea floors. They are a major factor in the ambient noise field and mask many useful seismic arrivals. For controlled source experiments shear wave resonances are a major source of incoherent, signal generated noise and coda. The peaks of the ambient noise spectra associated with the resonances, however, can be used to infer the sediment rigidity and thickness. The theory of Godin and Chapman (1999) has been used to infer shear velocity and sediment thickness from the resonance peaks in horizontal component power spectra for two sites in the Pacific. At ODP Site 843B (OSN-1), about 225km southwest of Oahu, the sediment thickness is known from drilling and we can infer from the resonances that the uppermost shear velocity is 76m/s. At the Hawaii-2 Observatory (H2O) Site, in 5000m water depth half-way between Hawaii and California we predict a sediment thickness of about 50m by assuming the same uppermost shear velocity as at OSN-1.