TY - JOUR
T1 - Seismo-acoustic signatures of shallow free gas in the Bornholm Basin, Baltic Sea
AU - Tóth, Zsuzsanna
AU - Spieß, Volkhard
AU - Jensen, Jørn Bo
N1 - Publisher Copyright:
© 2014 Elsevier Ltd.
PY - 2014/10/1
Y1 - 2014/10/1
N2 - Research on gas-charged sediments is generally based on identification and mapping with hydroacoustic methods, and seismic sections are typically verbally described. The terminology, however, does often not properly account for different instrumentation, as the seismic response of gas-charged sediments is frequency-dependent, and seismic appearance may vary with the instrumentation used. We therefore combine and compare the expressions of shallow gas in high frequency Parasound data and lower frequency multichannel seismic data for the Bornholm Basin, Baltic Sea, to generalize the descriptional approach and to indicate distinct imaging differences. Gas bubbles strongly scatter the acoustic energy of a high frequency signal, shallow gas appears therefore in Parasound data as a cloud of point scatterers and acoustic blanking. The seismic waves undergo reflection from the gassy sediment, but with sufficient transmission, and the top of the gassy sediment appears as a reversed polarity reflector. In seismic data, free gas can modify the seafloor reflection in different ways depending on the proximity of the gas front to the seafloor. High reflectivity at this interface causes reverberation of the water bottom reflector. Gas signatures also reveal relative measures about the amount and concentration of gas bubbles, distribution of bubble sizes, and the depth distribution of gas.
AB - Research on gas-charged sediments is generally based on identification and mapping with hydroacoustic methods, and seismic sections are typically verbally described. The terminology, however, does often not properly account for different instrumentation, as the seismic response of gas-charged sediments is frequency-dependent, and seismic appearance may vary with the instrumentation used. We therefore combine and compare the expressions of shallow gas in high frequency Parasound data and lower frequency multichannel seismic data for the Bornholm Basin, Baltic Sea, to generalize the descriptional approach and to indicate distinct imaging differences. Gas bubbles strongly scatter the acoustic energy of a high frequency signal, shallow gas appears therefore in Parasound data as a cloud of point scatterers and acoustic blanking. The seismic waves undergo reflection from the gassy sediment, but with sufficient transmission, and the top of the gassy sediment appears as a reversed polarity reflector. In seismic data, free gas can modify the seafloor reflection in different ways depending on the proximity of the gas front to the seafloor. High reflectivity at this interface causes reverberation of the water bottom reflector. Gas signatures also reveal relative measures about the amount and concentration of gas bubbles, distribution of bubble sizes, and the depth distribution of gas.
KW - Acoustic response
KW - Bubble resonance
KW - Interference
KW - Polarity reversal
KW - Reverberation
KW - Shallow gas
UR - http://www.scopus.com/inward/record.url?scp=84908376730&partnerID=8YFLogxK
U2 - 10.1016/j.csr.2014.08.007
DO - 10.1016/j.csr.2014.08.007
M3 - Article
VL - 88
SP - 228
EP - 239
JO - Continental Shelf Research
JF - Continental Shelf Research
SN - 0278-4343
ER -