2-D Velocity structure of Kerala-Konkan region using seismic traveltime Inversion

Existence of gas-hydrates in the marine sediments elevates the velocity of seismic waves, whereas even a small amount of underlying free-gas decreases the seismic velocity considerably. These changes in velocities can be used for the assessment of gas-hydrates. The traveltime inversion is an effective method to derive a 2-D velocity structure from the seismic data. We have applied the method to the Multi Channel Seismic (MCS) data for inferring gas hydrates and underlying free-gas in the Kerala-Konkan offshore region. A six layer 2-D velocity model has been generated from the reflection traveltimes using a ray tracing technique. The topmost sediment layer is ~165 m thick with velocity ranging from 1,680 m/s and 1,740 m/s. The second layer is ~110 m thick with velocity ranging between 1,890–1,950 m/s. The third layer with velocity of 2,100-2,180 m/s and thickness of ~125 m is interpreted as the gas hydrate-bearing sediment, below which the velocity drops to 1,620– 1,720 m/s. The velocity drop in the fourth layer (~180 m) may be due to the presence of free-gas. The bottommost sedimentary layer is marked with a velocity of 2600-2700 m/s.