Abstract
Multichannel seismic reflection data recorded between Itata (36°S) and Coyhaique offshores (43°S) were processed to obtain seismic images. Analysis of the seismic profiles revealed that weak and discontinuous bottom simulating reflectors were associated to basal accretion processes, while strong and continuous bottom simulating reflectors were associated to frontal accretion processes. This can be explained considering that during basal accretion processes, extensional tectonic movements due to uplifting can favour fluid escapes giving origin to weaker and most discontinuous bottom simulating reflectors. During frontal accretion processes (folding and thrusting), high fluid circulation and stable tectonic conditions however can be responsible of stronger and most continuous bottom simulating reflectors. Along the Arauco-Valdivia offshores, steep accretionary prisms, normal faults, slope basins, and thicker underplated sediment bed were associated to basal accretion, while along the Itata, Chiloe and Coyhaique offshores, small accretionary prisms, folding, and thinner underplated sediment bed were associated to frontal accretion.
Highlights
In marine seismic records, the Bottom Simulating Reflector (BSR) is a good indicator of gas hydrate presence
Analysis of the seismic profiles revealed that weak and discontinuous bottom simulating reflectors were associated to basal accretion processes, while strong and continuous bottom simulating reflectors were associated to frontal accretion processes
Along the Arauco-Valdivia offshores, steep accretionary prisms, normal faults, slope basins, and thicker underplated sediment bed were associated to basal accretion, while along the Itata, Chiloe and Coyhaique offshores, small accretionary prisms, folding, and thinner underplated sediment bed were associated to frontal accretion
Summary
The Bottom Simulating Reflector (BSR) is a good indicator of gas hydrate presence. The BSR has allowed defining the distribution of gas hydrate [1,2,3,4] along several continental margins. The BSR is associated with the acoustic interface between overlying sediment containing gas hydrate, which increases compressional seismic velocity, and underlying sediment containing free gas, which decreases compressional seismic velocity [2, 5]. The BSR has been identified in seismic sections in accretionary complexes along both convergent and passive margin settings [1]. Along the Chilean continental margin, the BSR is well reported by several geophysical cruises. The BSR is recognized along the accretionary prism [6,7,8,9,10,11]
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