Spectral characteristics of earthquakes recorded on the gulf of México seafloor and modeling of soft marine sediments

The overall goal of this work was to develop a costeffective method of characterizing offshore geotechnical sites in deep water. The generic approach was to place an ocean bottom seismograph on the seafloor and record ambient noise and distant earthquakes over periods of a month or more. Horizontal-to-vertical (H/V) spectral ratios were then calculated and used to characterize the local sediment response in terms of the distribution of motions with their respective resonant frequencies. One-dimensional wave propagation modeling using the stiffness matrix method was used to estimate sediment properties (mainly layering, shear stiffness, density and material damping) by matching the resonant frequency and amplification factors of the shallow sediment layers. The resulting sediment properties fall well within the expected range, indicating the potential of the proposed exploration approach for characterizing deep water sites.