Record-Breaking Ocean Drilling Reveals Why Japan's 2011 Tsunami Was So Deadly
"mrpg" writes:
Record-breaking ocean drilling reveals why Japan's 2011 tsunami was so deadly:
Researchers have uncovered a hidden feature beneath the Pacific Ocean that helps explain why Japan's devastating 2011 earthquake and tsunami became so destructive. The discovery also offers new clues that could improve forecasts of future megaquakes and tsunamis.
A new study found that a thin layer of soft, clay-rich sediment beneath the Japan Trench played a critical role in the disaster. Located just below the seafloor, this unusually weak layer allowed the fault to rupture all the way to the trench during the 2011 "megathrust" earthquake. As a result, the seafloor shifted by an extraordinary 130 to 200 feet, helping generate the massive tsunami.
"That's equivalent to the entire area between Los Angeles and San Francisco moving 130 to 200 feet in just six minutes," said Christine Regalla, an associate professor in Northern Arizona University's School of Earth and Sustainability and a co-author of the study. "We've never seen anything like that in the time we've been observing earthquakes. Based on what we understood, we didn't think that could happen."
The research, led by Regalla and more than a dozen scientists from around the world, was published in Science .
Most large earthquakes begin much deeper below Earth's surface. Regalla explained that when tectonic plates shift, the rupture that produces an earthquake usually occurs far underground. For example, the rupture that caused the 6.8 magnitude Nisqually earthquake in the Pacific Northwest in 2001 started about 32 miles beneath the seafloor.
The 2011 Japan earthquake was very different. The rupture reached only about 15 miles below the seafloor, allowing the fault to break much closer to the ocean bottom. The resulting magnitude 9.1 earthquake triggered one of the deadliest natural disasters in modern Japanese history, killing nearly 20,000 people and causing more than $200 billion in damage.
To understand why this happened, researchers traveled to the western Pacific aboard the research vessel Chikyu . They drilled about 26,000 feet into the ocean floor, recovered sediment samples, and analyzed the material. Guinness World Records recognized the expedition as the deepest scientific ocean drilling project ever completed.
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