The Main Himalayan Thrust has historically been responsible for a magnitude 8 to 9 earthquake every several hundred years. Credit: Warren Caldwell
(Phys.org)—Research by Stanford scientists focuses on geologic features and activity in the Himalayas and Pacific Northwest that could mean those areas are primed for major earthquakes.
Stanford geophysicists are well represented at the meeting of the American Geophysical Union this week in San Francisco. Included among the many presentations will be several studies that relate to predicting – and preparing for – major earthquakes in the Himalaya Mountains and the Pacific Northwest.
The AGU Fall Meeting is the largest worldwide conference in the geophysical sciences, attracting more than 20,000 Earth and space scientists, educators, students, and other leaders. This 45th annual fall meeting is taking place through Dec. 7 at the Moscone Convention Center in San Francisco.
The Himalayan range was formed, and remains currently active, due to the collision of the Indian and Asian continental plates. Scientists have known for some time that India is subducting under Asia, and have recently begun studying the complexity of this volatile collision zone in greater detail, particularly the fault that separates the two plates, the Main Himalayan Thrust (MHT).
Previous observations had indicated a relatively uniform fault plane that dipped a few degrees to the north. To produce a clearer picture of the fault, Warren Caldwell, a geophysics doctoral student at Stanford, has analyzed seismic data from 20 seismometers deployed for two years across the Himalayas by colleagues at the National Geophysical Research Institute of India.
The data imaged a thrust dipping a gentle two to four degrees northward, as has been previously inferred, but also revealed a segment of the thrust that dips more steeply (15 degrees downward) for 20 kilometers. Such a ramp has been postulated to be a nucleation point for massive earthquakes in the Himalaya.
Although Caldwell emphasized that his research focuses on imaging the fault, not on predicting earthquakes, he noted that the MHT has historically been responsible for a magnitude 8 to 9 earthquake every several hundred years.
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Added (05-December-2012, 4:08 AM)
Large Himalaya earthquakes may occur sooner than expected
While the rupture zones of recent major earthquakes are immune to similar-sized earthquakes for hundreds of years, they could be vulnerable to even bigger destructive temblors sooner than scientists suspect, according to analysis by University of Colorado seismologist Roger Bilham.
Bilham and his research colleagues explained that the magnitude 9.3 Indian Ocean earthquake of December 2004 showed scientists that a giant earthquake can rupture through a region with a recent history of quakes with magnitudes as large as 7.9 on the Richter Scale.
"Following what we learned in 2004, we believe that regions of the Himalaya that have recently experienced magnitude 7.8 earthquakes - like the Kangra district, a hundred years ago - may not be immune to a future larger earthquake," he said.
Bilham's research of Himalayan earthquakes in the last 1,000 years is part of findings presented in an invited talk, "Unprecedented massive earthquakes in the Himalaya driven by elastic strain stored within the Tibetan Plateau?" Dec. 7 at the American Geophysical Union's fall meeting in San Francisco.
Bilham recently returned from Kashmir, where he conducted a series of measurements along with Pakistani scientists to assess subsurface fault slip and damage in that region's October earthquake.
"The Kashmir event released almost 100 times less energy than the Sumatra-Andaman quake in 2004," he said. "The Kashmir rupture was about 16 times smaller in length and five times smaller in width, yet it flattened whole cities in its path."
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