This is the best analysis you're likely to find in the coming weeks, until the pipes can be inspected. Right now, "test gas" which is also Liquid Natural Gas (LNG) is leaking from the open pipes, and it will be 2-3 weeks before they can be inspected. Currently, there is so much gas dissolved in the water surrounding the eruptions at the surface, that boats cannot navigate the waters because the water literally does not weigh enough for boats to safely navigate. They don't float well in such water. Additionally, any spark would set the eruptions ablaze--creating sustained, mile-wide infernos of bubbling, boiling, flaming seas.
While eco-terrorist groups like Earth First might seem a likely culprit, they do not have the resources to pull off this kind of operation. The pipes are about 3 cm thick, surrounded by concrete and submerged under 80 meters of seawater. This was an extremely advanced assault.