Seismic attenuation in Faroe Islands basalts |
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| Authors: | F Shaw MH Worthington RS White MS Andersen UK Petersen the Seifaba Group |
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| Institution: | Department of Earth Sciences, Oxford University, Parks Road, Oxford, OX1 3PR, UK;, Bullard Laboratories, University of Cambridge, Madingley Road, Cambridge, CB3 0EZ, UK;, Geological Survey of Denmark and Greenland (GEUS), Oster Voldgade 10, DK-1350, Copenhagen, Denmark;, and University of the Faroe Islands, Noatun 3, FO-100, Torshavn, The Faroe Islands |
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| Abstract: | We analysed vertical seismic profiling (VSP) data from two boreholes at Glyvursnes and Vestmanna on the island of Streymoy, Faroe Islands, to determine the magnitude and causes of seismic attenuation in sequences of basalt flows. The work is part of SeiFaBa, a major project integrating data from vertical and offset VSP, surface seismic surveys, core samples and wireline log data from the two boreholes. Values of effective seismic quality factor (Q) obtained at Glyvursnes and Vestmanna are sufficiently low to significantly degrade the quality of a surface reflection seismic image. This observation is consistent with results from other VSP experiments in the North Atlantic region. We demonstrate that the most likely cause of the low values of effective Q at Glyvursnes and Vestmanna is a combination of 1D scattering and intrinsic attenuation due to seismic wave‐induced fluid flow within pores and micro‐cracks. Tests involving 3D elastic wave numerical modelling with a hypothetical basalt model based on field observations, indicate that little scattering attenuation is caused by lateral variations in basalt structure. |
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