Sumatra’s quake caused Earth to tremble like a bell: study
By Anwar Iqbal
WASHINGTON: Sumatra’s tsunami-triggering earthquake that killed more than 176,000 people in December, also shook the entire earth, leaving the planet trembling for weeks, say three scientific reports released on Friday The Sumatran-Andaman earthquake also created the longest fault rupture and the longest duration of faulting ever observed, says the report by an international group of seismologists published in the journal “Science.”
The quake displaced so much water from the Bay of Bengal and the Andaman Sea that the sea level worldwide was raised 0.004 inches.
“No point on Earth remained undisturbed,” wrote Roger Bilham of the University of Colorado. Researchers said the earthquake caused the planet to oscillate like a bell, which was measurable for weeks afterward. It caused ground movement of as much as 0.4 inches everywhere on Earth’s surface.
“Normally, a small earthquake might last less than a second; a moderate sized earthquake might last a few seconds. This earthquake lasted between 500 and 600 seconds (at least 10 minutes),” said Charles Ammon, associate professor of geosciences at Penn State University.
The quake released an amount of energy equal to a 100 gigaton bomb, said Mr. Bilham. And that power lasted longer than any quake ever recorded. The quake, centered in the Indian Ocean, also created the biggest gash in the Earth’s seabed ever observed, nearly 800 miles. Scientists estimated the average slippage (ground movement up and down) along the entire length of the fault was at least 5 meters (16.5 feet) — with some places being moved nearly 20 meters (50 feet).
Scientists have also upgraded the magnitude of the quake from 9.0 to between 9.1 and 9.3, a dramatically more powerful event. As a comparison: the ground shook 100 times harder during the Dec 26 earthquake than what was felt in the 1989 Loma Prieta quake in California. That 6.9 magnitude quake caused extensive damage from Santa Cruz to San Francisco.
The stunning power of Asia’s earthquake and tsunamis last December has left even veteran scientists in awe.
“I think it was humbling for everyone that analyzed the earthquake,” said Thorne Lay, professor of earth sciences and director of the Institute of Geophysics and Planetary Physics at the University of California, Santa Cruz. “We’re sitting in our laboratories working on the signals from this earthquake, trying to understand what happened scientifically, and then watching TV at night and seeing the death toll rising for weeks,” he said. Global broadband seismometers recorded the ground in Sri Lanka, a thousand miles from the epicentre, moved up and down by more than 9 centimetres.
The quake, second strongest ever recorded and the third most deadly in human history, released energy equivalent to the amount consumed by the entire United States in six months. It occurred where two of the giant plates that form the surface of the earth grind together. At the spot the Eurasian plate was being pulled downward by the descending Indo-Australian plate. The quake released the edge of the Eurasian plate, which sprang up, lifting the ocean floor and sending the sea water off in the giant wave and raised the sea level worldwide.
