caa a22 4500 463216296 CHVBK 20180405153157.0 cr unu---uuuuu 170326e20070601xx s 000 0 eng 10.1007/s00367-007-0073-3 doi (NATIONALLICENCE)springer-10.1007/s00367-007-0073-3 Phase-reversed seabed reflections in seismic data: examples related to mud volcanoes from the South Caspian Sea [Elektronische Daten] [Robert Evans, Simon Stewart, Richard Davies] The sediment-water interface is usually marked by an increase in acoustic impedance and is therefore displayed in a seismic section as a positive polarity reflection. Here, we use the term "seabed phase reversal” to describe areas of seafloor which are instead expressed as a negative polarity reflection in seismic data. We describe in detail a number of examples of seafloor phase reversals and use a simple one-dimensional geophysical model to test the hypothesis that they are the result of the presence of gas within the seafloor sediment. Our examples are all related to seismically imaged mud volcanoes located within the South Caspian Sea. Sections of phase-reversed seafloor at the summit area of these volcanoes have been mapped to reveal the existence of seafloor mud pools (salses) and recently erupted mud flows which show a strong similarity to smaller-scale features at onshore volcanoes in Azerbaijan. Synthetic geophysical modelling indicates that under the physical conditions likely to occur when the seabed sediment is gas-bearing, the seafloor will be expressed as a strong negative polarity reflection. Unlike other indicators of seafloor gas, such as pockmarks, which merely record the transient expulsion of fluids from sedimentary basins, seafloor phase reversals indicate the presence of gas in marine sediment at the time of survey acquisition. They therefore are of significance to engineering and site survey operations as well as the identification of biological communities and gas flux calculations. Springer-Verlag, 2007 Evans Robert 3DLab, School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, CF10 3YE, Cardiff, UK aut Stewart Simon BP Azerbaijan, Chertsey Road, Sunbury on Thames, TW16 7LN, Middlesex, UK aut Davies Richard CeREES (Centre for Research into Earth Energy Systems), Department of Earth Sciences, University of Durham, Science Labs, DH1 3LE, Durham, UK aut Geo-Marine Letters Springer-Verlag 27/2-4(2007-06-01), 203-212 0276-0460 27:2-4<203 2007 27 367 https://doi.org/10.1007/s00367-007-0073-3 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s00367-007-0073-3 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Evans Robert 3DLab, School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, CF10 3YE, Cardiff, UK aut NATIONALLICENCE 700 1- Stewart Simon BP Azerbaijan, Chertsey Road, Sunbury on Thames, TW16 7LN, Middlesex, UK aut NATIONALLICENCE 700 1- Davies Richard CeREES (Centre for Research into Earth Energy Systems), Department of Earth Sciences, University of Durham, Science Labs, DH1 3LE, Durham, UK aut NATIONALLICENCE 773 0- Geo-Marine Letters Springer-Verlag 27/2-4(2007-06-01), 203-212 0276-0460 27:2-4<203 2007 27 367 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer