19^th International CODATA Conference
Category: Gas Hydrates

Seismic velocity structure at a gas-hydrate reflector, offshore western India, from full waveform inversion

Kalachand Sain (saink@ngri.res.in), N.K. Thakur ⁽nkthakur46@yahoo.com⁾ and S.I. Reddi
National Geophysical Research Institute, India

A bottom simulating reflector (BSR) is visible at 400 m below the seafloor lying at 1900 m on a seismic section in the western continental margin of India. To derive the fine-scale velocity structure across the BSR, we perform full-waveform inversion of multi-channel seismic data at a CDP gather. The result shows a 25 m zone of hydrated layer in which P-wave velocity suddenly increases from a value of 1.88 to 2.25 km/s and then drops to a value of 1.84 km/s. The low-velocity zone below the BSR is very thin (~10 m). The possible mechanism for the formation of BSR is mainly due to presence of gas-hydrates above the BSR. AVO attributes, analysed across the BSR, also do not show any evidence of gas below the BSR. Results of Monte-carlo traveltime inversion, waveform inversion and attribute analysis will be presented. A probable mechanism for the origin of BSR will also be proposed.