Seismic analysis and distribution of a bottom-simulating reflector (BSR) in the Chilean margin offshore of Valdivia (40° S) |
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| Authors: | Cristián Rodrigo Emilio Vera Antonio González-Fernández |
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| Institution: | 1. Institut für Geowissenschaften, Universität Friedrich-Schiller Jena, Burgweg 11, 07749 Jena, Germany;2. Institut für Geophysik, Universität Hamburg, Bundesstraße 55, 20146 Hamburg, Germany;3. FB Geowissenschaften, Universität Bremen, Postfach 330 440, D-28334 Bremen, Germany;4. FUGRO OSAE GmbH, 28359 Bremen, Germany;5. School of Environment, University of Auckland, Private Bag 92091, Auckland 1142, New Zealand |
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| Abstract: | Multi-channel seismic (MCS) reflection data recorded offshore from Valdivia (40° S), in the Chilean margin, were processed to obtain a seismic image to establish structural characteristics and relate them to the presence of the bottom-simulating reflector (BSR). Seismic structure velocity of the BSR was determined using 1-D forward modeling. Recorded seismograms for two representative common mid-point (CMP) gathers were compared with synthetics, using different physical parameters to fit the waveforms. Our results confirm the presence of gas hydrates above the BSR. The BSR spatial continuity appears to be either interrupted or irregular due to the presence of faults. Tectonic movements can change the gas hydrate stability zone and consequently the BSR disappears or becomes weaker. Structural and topographic factors, differences in concentration, vertical distribution characteristics and internal structure of gas hydrates can influence BSR amplitude behavior. Variability in the concentration, volume, and extra supply of free gas coming from faults could be the main factors in the change of BSR amplitudes. The inclusion of the attenuation factor in the modeling supports the existence of free gas below the BSR. It is possible that the free gas below the BSR is distributed in bubbles or “bags”. |
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