Gas-hydrates have received global attention as a feasible major unconventional hydrocarbon energy resources. Hence, delineation is very imperative for evaluating the resource potential. Gas-hydrates are found out in shallow sediments of outer continental margins and permafrost regions, and have been recognized mainly by seismic experiment based on an anomalous reflector, known as the bottom simulating reflector or BSR. This is a physical boundary between gas hydrate-bearing sediments above and free-gas saturated sediments below, and mimics the shape of seafloor, has opposite polarity with respect to sea floor and crosscuts underlying dipping sedimentary strata. Since gas-hydrates have been recovered without a BSR and even have not been