"We're measuring the temperature across the fault zone after the earthquake," Chester said. "It's as if there's much lower friction than one would expect, and they can release a substantial amount of their total stress."Īnalysis of rock samples gathered from one borehole and scientific instruments placed within another will glean further insights into the huge quake. "However, increasingly, it's becoming clear that these plate boundary faults are weak," Chester added. "Studies over the past 30 or 40 years have shown that it's very hard to slide rock against rock due to the amount of friction involved, and studies have shown that in conventional earthquakes and smaller faults, only 10 percent or some other small fraction of the stress is releasedwhen these blocks of rock slip past each other." "It is very surprising that this can occur," Chester said. The researchers found the present amount of stress on the fault is nearly zero, revealing the earthquake released nearly all the stress there. By continuously measuring how electrically resistant the rock was as the borehole was drilled, the scientists could deduce the magnitude and even direction of the stress in the rock. The more stressed rock is, the more fractures result when drills bore into it, and the more fractured rock is, the lower its electrical resistivity (meaning the current flows more easily through it). To measure the amount of stress in the rock, the investigators analyzed how resistant rock in the borehole was to the flow of electric current. We were delayed a lot by weather and by key equipment failures, but with perseverance and highly capable drilling engineers, we were able to succeed." "Another challenge was the 'rapid response' nature of this expedition - most scientific drilling operations like this in the deep ocean take years of planning, and we only had 13 months. "The expedition was incredibly challenging - we were really pushing the depth limits and our equipment at this site," Chester said. The expedition analyzed rock as they drilled boreholes 2,790 feet(850 meters) into the seafloor about 22,600 feet (6,890 m) underwater. To explore this possibility, researcher Weiren Lin at Japan's Agency for Marine-Earth Science and Technologyand colleagues set out aboard the scientific drilling vessel Chikyu to about 60 miles (93 kilometers) from the epicenter of the quakeabout a year after the disaster.
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