The organic chemistry was borrowed from the oil industry, which has invested millions in measuring how rocks are heated based simply on the properties of organic matter in those rocks — though the cooking usually takes millions of years, not seconds and minutes, like earthquakes.
In Alaska, the biomarkers were diamondoids, carbon and hydrogen heated until they take on the same basic structure as diamonds. By modeling the heat needed to create diamondoids, Savage and her colleagues estimate the earthquake they found was about a magnitude 7 or magnitude 8, with a temperature rise of between 1,540 and 2,140 degrees Fahrenheit (840 to 1,170 degrees Celsius) and between 3 to 30 feet (1 to 9 meters) of movement. The findings were published Jan. 6 in the journal Geology. [Shine On: Photos of Dazzling Mineral Specimens]
"We're very excited; it's one of the first times we've been able to do this with a new method," Savage said.
Savage noted that this earthquake thermometer only works on faults in sedimentary rocks that carry organic material, and that not all earthquakes will generate a lot of heat. In California, along an ancient strand of the San Andreas Fault called the Punchbowl Fault, the team found a temperature rise of only 1,150 F (625 C), despite geologic evidence of past earthquakes.
The group has several new projects in the works. They're investigating rocks from Japan's JFAST drilling site, at the source of the 2011 Tohoku earthquake, and working on the San Andreas Fault deep drilling project, to see if the slow-moving part of the San Andreas Fault ever had large earthquakes. They are also running laboratory tests to customize those petroleum-industry chemical equations and to better understand the link between temperature on faults and organic matter. And someday, Savage would like to create a "heat map" of a fault.
"We're hoping that being able to walk up to an outcrop and fingerprint this kind of slip, which may help tell us how earthquakes get started, and maybe how they stop," Savage said.
"A fault plane is hundreds of kilometers long and tens of kilometers wide, and maybe the strength of that fault is determined by very small patches holding most of the resistance to sliding," Savage said. "Understanding how stress is distributed on faults is a very important question toward understanding when a fault is getting close to actually having an earthquake."
Original article at LiveScience's OurAmazingPlanet.
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