A First-Order Thermo-Seismic Framework for Atypical Bottom-Simulating Reflector Responses in the Northern South China Sea

Atypical bottom-simulating reflector (BSR)-like responses in structurally complex gas-hydrate provinces are difficult to interpret using morphology alone. This review develops a literature-constrained, physics-guided framework that organizes such responses in the northern South China Sea along three descriptive axes—continuity, geometry/deformation, and multiplicity—retaining six commonly reported end-member expressions as non-mutually exclusive working types. Published observations from the Shenhu area and the Qiongdongnan Basin are examined using a first-order thermo-seismic workflow comprising hydrate phase-equilibrium modeling, acoustic-impedance analysis, and convolutional synthetic seismic modeling. Over the reported GMGS3 drilling-water-depth range and measured geothermal gradients, the model predicts BSR depths of approximately 146–308 mbsf, overlapping the reported 230–400 mbsf interval. At W19, the observed BSR falls within this envelope; at SH-W07-2016, inverse calculations match the shallower interface with a measured-range gradient, while the deeper one requires cooler conditions. An illustrative impedance calculation yields a hydrate-to-gas reflection coefficient of approximately −0.25, consistent with the negative polarity of typical BSRs. The framework supports the interpretation of ambiguous BSR-like responses by testing their physical admissibility, identifying competing geological explanations that a single morphology cannot exclude, and indicating what further seismic or drilling evidence would be needed to discriminate among them; it does not validate morphology–mechanism assignments.