Seismic attenuation of Atlantic margin basalts: observations and modeling

Maresh, J. and White, R. S. and Hobbs, R. W. and Smallwood, J. R. (2006) Seismic attenuation of Atlantic margin basalts: observations and modeling. Geophysics, 71 (6). B211-B221; doi:10.1190/1.2335875. DOI

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Paleogene basalts are present over much of the northeastern Atlantic European margin. In regions containing significant thicknesses of layered basalt flows, conducting seismic imaging within and beneath the volcanic section has proven difficult, largely because the basalts severely attenuate and scatter seismic energy. We use data from a vertical seismic profile (VSP) from well 164/07-1 that penetrated 1.2 km of basalt in the northern Rockall Trough west of Britain to measure the seismic attenuation caused by the in-situ basalts. The effective quality factor Qeff of the basalt layer is found from the VSP to be 15-35, which is considerably lower (more attenuative) than the intrinsic attenuation measured on basalt samples in the laboratory. We then run synthetic seismogram models to investigate the likely cause of the attenuation. Full waveform ID modeling of stacked sequences of lava flows based on rock properties from the same well indicates that much of the seismic attenuation observed from the VSP can be accounted for by the scattering effects of multiple thin layers with high impedance contrasts. Phase-screen seismic modeling of the rugose basalt surface at the top-of-basalt sediment interface, with the magnitude and wavelength ofthe relief constrained by a 3D seismic survey around the well, suggests that surface scattering from this interface plays a much smaller role than internal scattering in attenuating the seismic signal as it passes through the basalt sequence.

Item Type: Article
Uncontrolled Keywords: 2006 AREP IA46
Subjects: 99 - Other
02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Geophysics
Volume: 71
Page Range: B211-B221; doi:10.1190/1.2335875
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:03
Last Modified: 23 Jul 2013 10:07

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