Tuesday, July 31, 2012

[Geology2] Methane Seeping From Fault Off Del Mar



Methane seeping from fault off Del Mar

Written by Gary Robbins
San Diego Union-Tribune
7 a.m., July 26, 2012

The Scripps Institution of Oceanography says that it has discovered "convincing evidence" that methane is seeping from a sub-sea earthquake fault about 20 miles west of Del Mar, the first leak of its kind found off San Diego County.

Graduate students working from the research vessel Melville made the discovery 3,400 feet below the ocean's surface, above the San Diego Trough, a fault zone that extends for about 93 miles in a line that runs from North County into Mexican waters. Seismologists say the fault is capable of producing quakes ranging in magnitude from 6.0 to 7.7.

Methane is odorless, and therefore does not appear to be related to the unusual smell that many people have detected along the North County coastline in recent days. The colorless gas also is highly flammable. But the seep off Del Mar does not appear to pose a public safety hazard.

Methane - a fuel that's also a greenhouse gas -- is commonly found underground and it is not unusual for the gas to seep out of faults. Such leaks are of great interest to scientists because they can contribute to ecosystems that support unusual marine life.

In announcing its discovery, Scripps said in a statement that, "Organisms collected from the site include thread-like tubeworms called siboglinids and several clams. Siboglinids lack a mouth and digestive system and gain nutrition via a symbiotic relationship with bacteria living inside them, while many clams at seeps get some of their food from sulfide-loving bacteria living on their gills.

"While food is scarce in much of the cold, dark ocean depths, it is abundant at seeps due to the bacteria that proliferate around the methane source. Microbes there are eaten by worms, snails, crabs and clams, leading to a rich and productive community that helps sustain the surrounding deep-sea ecosystem."

Scripps plans to return to seepage area in December to conduct further research.

Source: http://www.utsandiego.com/news/2012/jul/26/methane-leaking-fault-del-mar/

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