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Istanbul advised to brace for major quake
The probability is high that Istanbul, Turkey, will experience a major earthquake in the near future, an international team of scientists report in today's Science.
" In the next 30 years, the chance is roughly 60 percent," said Thomas Parsons, a geophysicist with the U.S. Geological Survey.
Parsons and his colleagues urge a calm response to their report. Though an earthquake could occur tomorrow, they hope their finding will serve as advance warning to Turkish citizens to minimize hazards.
Safety measures include fastening bookshelves and cabinets to walls, developing a safety plan in case of an earthquake and keeping a survival kit at the ready, said Parsons.
In arriving at a probability of 62 percent (with a 15 percent margin of error) for an episode of strong shaking in Istanbul, the researchers took into account the stress transfer from a magnitude 7.4 earthquake in Izmit, Turkey in August 1999.
Whenever an earthquake occurs at one point along a fault, it may create a higher stress level at another point.
"Beginning in 1939, there were events well to the east of Istanbul that seems to have started a progressive sequence to the west. The question is, will the sequence continue further?" said Parsons. "Unfortunately, we think the answer is yes."
The researchers say that traditional models, based mainly on the average time between events, underestimate earthquake hazards on the North Anatolian fault system, where Istanbul lies, because they do not reflect the buildup of stress as earthquakes progress down the fault.
The researchers assembled a catalog of major earthquakes occurring along the Yalova, Izmit, Prince's Islands and Marmara Sea faults — all faults in the North Anatolian system — since 1500.
"The basic idea was to convert historical descriptions into an idea of where earthquakes happened and how big they were," said Ross Stein, Parsons' colleague at the U.S. Geological Survey.
Two earthquakes occurred on the Izmit fault in 1719 and 1999, and three earthquakes ruptured the Yalova fault in 1509, 1719 and 1894, the researchers found. The central Marmara fault has been silent since 1509, and the Prince's Islands fault last broke in 1776.
"Thus, at least two of the four faults are likely late in their earthquake cycles," the researchers report in Science.
Parsons and his colleagues are currently conducting a similar earthquake risk analysis for the San Francisco Bay Area in California.
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