Researchers measured the frictional heat from the fault slip during an earthquake, and determined it was surprisingly low during the Tohoku-Oki earthquake in Japan that triggered a tsunami and took over 18,000 lives in 2011.
"The Tohoku fault is more slippery than anyone expected," said Emily Brodsky, a geophysicist at the University of California, Santa Cruz, and coauthor of three papers on the Tohoku-Oki, said in a University of California, Santa Cruz news release.
Friction causes heat, which is why one's hands warm up when they are rubbed together; the researchers found they could determine the amount of friction emitted by measuring the temperature of a fault after an earthquake.
"It's been difficult to get this measurement because the signal is weak and it dissipates over time, so we needed a big earthquake and a rapid response," Brodsky, a professor of Earth and planetary sciences at UCSC, said.
In 2012 researchers drilled into the Tohoku fault and installed a temperature observatory.
The team believes the unusual amount of slip could have been a huge contributor of the 50 meters of displacement that happened during the deadly earthquake. The slickness could be attributed to clay material.
"The large slip at shallow depths contributed to the tsunami that caused so much damage in Japan. Usually, these earthquakes don't rupture all the way to the surface," first author Patrick Fulton, said.
The earthquake took place between two tectonic plates (a "subduction zone"). The team found the area where the quake originated was much deeper than other parts of the fault. The fault was ruptured all the way to the sea floor.
Stress released during the earthquake is believed to build in the deep areas of the fault between the two "locked" plates. Scientists had not expected the shallow areas of the fault to take on as much stress. The fact that the frictional stress was so low during the earthquake suggests it was low when the earthquake started or was all released at the same time.
"It's probably a combination of both--the fault was pretty slippery to begin with, and whatever stress was on the fault at that shallow depth was all released during the earthquake," Fulton said.
Information on the earthquake attributed to LiveScience.
