The conditions required for the formation of natural gas hydrates occur frequently on the Earth’s continental margins (apart from a smart fraction associated with the Artic Permafrost): - Is there any specific reason associated with these kind of occurrence?
Depth (isolation and pressure), volcanic activities (quick temperature changes and released materials), and seismic activities (releasing liquid from different layers) are all common on the Earth's continental margins. These phenomena and the caused changes can result in the accumulation of gas hydrates in a long period.
Natural gas hydrates are crystalline structures that combine natural gases and water under appropriate temperature and pressure conditions. Natural gases and water are found throughout the Solar System, even in interplanetary space. It is geologically reasonable to conjecture that these natural components were incorporated into the proto-Earth and that hydrates formed as soon as the appropriate temperature and pressure conditions evolved. On Earth today, a planet long dominated by plate tectonics, hydrates of methane and other gases, hydrocarbons, carbon dioxide, and hydrogen sulfide, are found across polar zones and in many marine sediments. It is almost certain that hydrates have existed at least as long as have plate tectonics, with these tectonics creating geologic circumstances similar to those at present although distributed differently over the Earth’s surface.
Petroleum exploration to ever-greater water depths as well as greater depths into the subsurface is continuing to reveal that continental margins, both active and passive, are surprisingly complex, dynamic, and often surprisingly structurally weak. Numerous processes interrelate on scales from the minute to the regional and in intricate manners. The complexity of features observed along margins, by tools that observe the small to the large, from bottom photographs and cores to industrial multichannel seismic reflection records, respectively, implies a diverse geology and stress regimes. These interrelationships are illustrated along a dip section that trends from northwest to southeast and starts at the continental shelf break, crosses the upper continental slope and a mid-slope basin and proceeds down the western flank of the pronounced Mississippi Canyon along the northern Gulf of Mexico continental margin. The boundaries of the mid-slope basin are defined by two diapiric salt structures. This specific description is made to facilitate understanding of the geologic complexities, including a role for hydrates that appear to be common along many continental margins.
Numerous near-seafloor faulted blocks are observed on boomer, chirp sonar, and G.I.gun profiles along the slope-descending seismic data. These data also show the sediments near the sea floor to be characterized by weak, yet interpretable, reflectors. The weak reflectivity may indicate cementation by gas hydrates. In places, the weak reflectors are underlain by chaotic, sharply stronger reflectivity typical of free gas.
The boomer and chirp profiles over the mid-slope basin exhibit vertically oriented structures within the near-seafloor sediments, which may mark pathways of small-scale fluid expulsion, the fluid possibly being produced by dissociation of gas hydrates. The pathways may coincide with sites of weakness produced by gravity-induced tension. Also, mound-shaped features occur on the sea floor within the mid-slope basin. One of these has been documented to be a mud diapir containing gas hydrates.
Heat-flow measurements over the mid-slope basin indicate that the sea floor there is within the hydrate stability zone and that the zone is some 500m thick. Heat flow at the base of the hydrate-bearing diapir is 10-fold greater than that at its summit. Combining the high heat flow with seismic evidence that the base of the diapir comprises a fault scarp leads to an interpretation that warm fluids are flowing from an “open” fault there.
The tectonic matrix is complex and dynamic. Overall area motions are gravity-driven subsidence with evidence of rising tectonics: local thermal gradients, buoyant salt, mud diapirism, and fluid expulsion. The shallow and regional geology thus provide detailed input for ever-more-quantifiable margin-spanning models.
Two principal ideas are put forth; 1) that hydrates appear to be features whose existence and permanence are really ancient and 2) that a general description of contemporary (uppermost Holocene) hydrate occurrence within the geologic complexity of the northern Gulf of Mexico can be made from analyzing recently-collected data. Previous high-stand events presumably created similar geologic situations: the present may be a key to the past.
https://csegrecorder.com/articles/view/natural-gas-hydrates-earth-constituents-impacting-sediment-strength