Estimating the thermal structure of oceans using seismic and fluid-dynamic modeling

Scope and Method of Study: Rise and withdrawal of shale diapirs in an offshore basin located along the Indian east coast creates mounds and mini-basins at the seafloor. Faults associated with these mounds channel warm fluid from the deeper subsurface into ocean water. We present a method to estimate the fluid temperature and flux using seismic inversion and fluid dynamic modeling.;Findings and Conclusions: Inversion of seafloor reflection times from two mutually perpendicular, multichannel seismic (MCS) profiles acquired over a bathymetric mound show that acoustic velocity (VP) of the ocean water increases by ∼10m/s at the mound compared to the background. The velocity structure of the ocean water is transformed to the corresponding temperature structure using Del Grosso's relationship and validated with a CTD profile near the mound. Next, using computational fluid dynamics a numerical experiment simulating the release of a warm water plume into an overlying stationary water column is set up. The temperature gradient of the stationary water column is from the VP gradient in the inverted model away from the mound. The temperature of the plume is set 2.5°C higher than the background seafloor temperature and corresponds to the elevated VP at the mound. Multiple combination of plume velocity and inlet width indicate that the temperature structure estimated by seismic modeling can be replicated by a continual fluid seepage with the initial plume velocity of 5 mm/s across the entire width of the mound (∼1 km) for ∼6 years.