I assume you are asking this in relation to extracting energy by mining gas hydrates on the ocean floor. Unlike deep water drilling for oil such as the exploration and extraction being done by Brazil in the South Atlantic, gas hydrates are usually not found under thousands of meters of cap rock. Brazil’s offshore oil fields lie under an enormous salt deposit that ensures the stability of the ocean floor. Gas hydrates often lie within a few meters of the ocean floor surface. Furthermore they tend to be close to where the continental plates ride over the ocean crust. These would be inherently unstable areas for any type of mining so the technology that needs to be developed has to take into consideration the geological formations in the vicinity of the gas hydrate deposits. Currently scientists and engineers express concern about the potential to cause underwater landslides. Landslides are not earthquakes but they can have as significant an impact on the water that lies above the zone in which they occur. That is why they can cause tsunamis.
Hydraulic fracturing and small earthquakes in proximity to the injection sites are correlated. Undersea hydraulic fracturing of oil shale deposits could cause earthquakes on the ocean floor. The likelihood of large displacement from such earthquakes is extremely small.
]]>