Seismoacoustic Study of the Shallow Gas Transport and ... - E-LIB

Chapter 2
reflections. These transparent seismic reflections represent mud flows deposited during
eruptive episodes. Therefore, three mud chambers represent three periods of intense
eruptive activity.
Figure 10 Structural and evolutionary of the MSU mud volcano. Red patches indicate the gas/gas hydrate
reservoirs. Dark green arrows show the gas/fluid migration pathways. Light green arrows show the gas may
derive from the shallow subsurface. Dotted lines indicate the downward bending of sediment layers in the
feeder channel, which can be traced towards the undisturbed sedimentary strata. Two mud chambers and a
small chamber are included. Faults are indicated the vertical black lines.
Feeder channels of mud volcanoes are interpreted in six locations as the main
pathways for gas and fluid upward migration. Main characteristics are a flat top, wide
mud chambers and wide feeder channels, which indicate low mud viscosity, transport of
large gas and mud volume and long lasting activity, similar to the evidence provided by
Somoza et al. (2012). Downward bending of reflections at the base of mud chambers
reveals a significant collapse due to a volume loss and depressurization associated with
mud eruptions. On the flanks of the feeder channel, bright spots and blurred margins
indicate the lateral transport of gas into the surrounding high permeable (sandy) sediment
layers. This may originate from free gas transported with the mud, but also from gas
hydrate decomposition in case that the mud eruption provides fast vertical heat transport.
Isotopic analysis showed that the gas is of mixed biogenic and thermogenic origin
(Ivanov et al., 1996; Limonov et al., 1997). The biogenic gas may derive from the
shallow subsurface, which is rich in the terrigenous organic matter from the Danube and
Dniepr rivers (Limonov et al., 1997). Particularly the thermogenic gas migrates upward
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