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For the first time, scientists have watched the Earth heal itself after an earthquake.
No one knows for sure how faults heal, and the observations from the Wenchuan drilling project offer more questions than answers. But the project's long-term monitoring of fractures opening and closing on a fault offers a series of fascinating puzzles for scientists to solve, said Chris Marone, a geophysicist at Penn State University who was not involved in the study. Rapid response drillingThe Wenchuan project team tracked the healing process through a series of deep boreholes drilled through the fault. The study is part of an ongoing global effort to examine faults immediately after earthquakes, in hopes of checking the results of decades of laboratory experiments and computer modeling.
"We already know there are a lot of reasons real faults may not behave the way we think they do," said Emily Brodsky, a study co-author and geophysicist at the University of California, Santa Cruz. "If we're going to gain some actual new insights or go well beyond where our imaginations went before, we need the real deal," she said.
For 18 months, the team monitored the fault's permeability, a measure of how quickly water flows through the rock. Permeability is a stand-in for damage on the fault, Brodsky said — as the fault heals, the area should become less permeable to fluids. The experiment tracked the ebb and flow of fault fluids from tidal forces, the same tugs from the sun and moon that create ocean tides. Remote triggering
But they did solve another puzzle: Six short-term jumps in the permeability, random events with no link to local aftershocks or equipment problems. The team eventually realized shaking from big but distant earthquakes broke open healed sections of the fault, Brodsky said. Some of the remote culprits include the March 2011 Japan earthquake and a magnitude-7.8 earthquake in Sumatra in April 2010.
Earthquakes on one fault are known to damage other nearby faults, and big earthquakes can trigger new temblors worldwide. But this is the first time effects of dynamic stress — the passing of seismic waves — have been seen on a fault with such detail.
Editor's Note: This article was originally published by Science Daily, here, and is licenced as Public Domain under Creative Commons. See Creative Commons - Attribution Licence.
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