Phase-reversed seabed reflections in seismic data: examples related to mud volcanoes from the South Caspian Sea |
| |
Authors: | Robert J Evans Simon A Stewart Richard J Davies |
| |
Institution: | (1) 3DLab, School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE, UK;(2) BP Azerbaijan, Chertsey Road, Sunbury on Thames, Middlesex, TW16 7LN, UK;(3) CeREES (Centre for Research into Earth Energy Systems), Department of Earth Sciences, University of Durham, Science Labs, Durham, DH1 3LE, UK |
| |
Abstract: | 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. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|