Characterization of the upper oceanic crust using high-resolution seismic amplitude modeling

We examine the links between structural and lithological changes in the upper oceanic crust and seismic amplitude changes by applying modeling techniques in order to extend the conventional uses and limits of seismic data. Using highresolution velocity and density borehole profiles from Ocean Drilling Program Hole 504B, we evaluate modeling methods and study the mechanisms of seismic attenuation in this layered porous environment. Good agreement of full-waveform synthetic seismograms with field seismic data is observed in travel time as well as in waveform shape and amplitude variations. Large seismic energy losses in the upper oceanic crust are observed where the formation consists of cyclic sequences of high-and low-porosity units, which demonstrates that energy loss in the upper oceanic crust is dominated by the effects of scattering alone. A fault zone and the boundary between seismic layers 2 and 3 are observed by amplitude changes on both synthetic and observed reflection records. The seismic amplitude, therefore, may indeed be used to map porosity and other lithologic variations.

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