Solid Earth Discussions www.solid-earth-discuss.net 1869-9537 2 1 2010 10.5194/sed-2-1-2010 http://www.solid-earth-discuss.net/2/1/2010/ http://www.solid-earth-discuss.net/2/1/2010/sed-2-1-2010.html http://www.solid-earth-discuss.net/2/1/2010/sed-2-1-2010.pdf 1 17 2010-02-08 Some improvements in subbasalt imaging using pre-stack depth migration I. Flecha R. Carbonell R. W. Hobbs H. Zeyen Departament de Estructura i Dinámica de la Terra CSIC-Institut de Ciències de la Terra "Jaume Almera" C/ Lluís Sole i Sabarís s/n, 08028 Barcelona, Spain Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK Departement des Sciences de la Terre, Universite de Paris-Sud, Bat. 503, 91405 Orsay Cedex, France Subbasalt imaging can be improved by carefully applying pre-stack depth migration. Pre-stack depth migration requires a detailed velocity model and an accurate traveltime calculation. Ray tracing methods are fast but, often fail in calculating traveltimes in complex models, specially, when they feature high velocity contrasts. Finitte difference solutions of the eikonal are more stable and can produce a traveltime field for the whole model avoiding shadow zones. A synthetic test was carried out to check the performance of a new pre-stack depth migration algorithm in a model that features a high velocity layer surrounded by lower velocities. The results reasonably reproduce the original model. The same scheme was used to process long-offset reflection data from the Faroe Shelf where conventional techniques (stack) were insufficient to assess the structure under a basalt layer. Pre-stack depth migration produced an improved image which recovered the main features in the stacked section and allowed to identify some subbasalt coherent events. Fliedner, M M. and White, R S.: Sub-basalt imaging the Faeroe-Shetland Basin with large-offset data, First Break, 19, 247–252, 2001. Fliedner, M M. and White, R S.: Depth imaging of basalt flows in the Faeroe-Shetland Basin, Geophys. J. Int., 152, 353–371, 2003. Forel, D., Benz, T., and Pennington, W D.: Seismic Data Processing with Seismic Un*x, Society of Exploration Geophysicists, 2005. Fruehn, J., Fliedner, M M., and White, R S.: Integrated wide-angle and near-vertical subbasalt study using large-aperture seismic data from the Faroe-Shetland region, Geophysics, 66, 1340–1348, 2001. Hole, J A. and Zelt, B C.: Three-dimensional finite-difference reflection travel times, Geophys. J. Int., 121, 427–434, 1995. Hughes, S., Barton, P J., and Harrison, D.: Exploration in the Shetland-Faeroe Basin using densely spaced arrays of ocean-bottom seismometers, Geophysics, 63, 490–501, 1998. Maresh, J. and White, R S.: Seeing through a glass, darkly: strategies for imaging through basalt, First Break, 23, 27–33, 2005. Martini, F. and Bean, C J.: Interface scattering versus body scattering in subbasalt imaging and application of prestack wave equation datuming, Geophysics, 67, 1593–1601, 2002. Noe-Nygaard, A. and Rasmussen, J.: Petrology of a 3000 metre sequence of basaltic lavas in the Faroe Islands, Lithos, 1, 286–304, 1968. Raum, T., Mjelde, R., Berge, A M., Paulsen, J T., Digranes, P., Shimamura, H., Shiobara, H., Kodaira, S., Larsen, V B., Fredsted, R., Harrison, D J., and Johnson, M.: Sub-basalt structures east of the Faroe Islands revealed from wide-angle seismic and gravity data, Petrol. Geosci., 11, 291–308, 2005. Richardson, K R., White, R S., England, R W., and Fruehn, J.: Crustal structure east of the Faroe Islands: mapping sub-basalt sediments using wide-angle seismic data, Petrol. Geosci., 5, 161–172, 1999. Smallwood, J R., Towns, M J., and White, R S.: Thew structure of the Faeroe-Shetland Trough from integrated deep seismic and potential field modelling, J. Geol. Soc., 158, 409–412, 2001. Sørensen, A B.: Cenozoic basin development and stratigraphy of the Faroes area, Petrol. Geosci., 9, 189–207, 2003. Trinks, I., Singh, S C., Chapman, C H., Barton, P J., Bosch, M., and Cherrett, A.: Adaptative traveltime tomography of densely sampled seismic data, Geophys. J. Int., 160, 925–938, 2005. White, R S., Fruehn, J., Richardson, K R., Cullen, E., Kirk, W., Smallwood, J R., and Latkiewicz, C.: Faroes Large Aperture Research Experiment (FLARE): imaging through basalt, Geological Society, 1243–1252, 1999. White, R S., Smallwood, J R., Fliedner, M M., Boslaugh, B., Maresh, J., and Fruehn, J.: Imaging and regional distribution of basalt flows in the Faroe-Shetland Basin, Geophys. Prosp., 51, 215–231, 2003. Yilmaz, O.: Seismic data processing, Society of Exploration Geophysicists, Tulsa, 1987. Zelt, C A. and Smith, R B.: Seismic traveltime inversion for 2-D crustal velocity structure, Geophys. J. Int., 108, 16–34, 1992.