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article imageNew study shows massive earthquake in Bay area 'imminent'

By Greta McClain     Oct 14, 2014 in Science
San Francisco - A new study of the San Andreas Fault system has scientists worried that a potentially devastating and deadly earthquake in parts of the Pacific Northwest is imminent.
The study, which was released on Monday, was conducted by scientists from the U.S. Geological Survey (USGS) and San Francisco State University. In the study, scientists looked at data gathered over the past 35 years, searching for evidence of fault creep. Fault creep is a term used to describe slow, constant slippage along fault lines which release pressure but do not result in an earthquake.
According to the study, 60 percent of the fault system has shown evidence that energy has been released through fault creep, ranging from 0.1 to 25.1 mm (.004 to 1 inch) per year. However, roughly one-third of the 1,250 miles of the San Andreas fault system, showed no signs of fault creep and were essentially locked.
The amount of fault creep can reduce the potential magnitude of an earthquake. Likewise, a lack of fault creep results in increased stress along the fault line, which can result in more powerful earthquakes. James Lienkaemper, a research geophysicist at the USGS and co-author of the study, said:
"The extent of fault creep, and therefore locking, controls the size and timing of large earthquakes on the Northern San Andreas Fault system. The extent of creep on some fault sections is not yet well determined, making our first priority to study the urban sections of the San Andreas, which is directly beneath millions of Bay Area residents."
The data gathered also allowed scientists to calculate the recurrence rates of earthquakes along the fault system and predict the probable timing and size of future earthquakes. According to a CBS Sacramento report, three segments along the fault system and one other fault in the region have enough built up pressure to unleash one or more earthquakes as large as 6.8 magnitude or higher. These faults include the Hayward Fault, the Rodgers Creek Fault, the Green Valley Fault and the Calaveras Fault. The findings are of particular concern to scientists since all four faults lie directly underneath cities.
Map showing the major faults in the Bay Area  with Hayward in medium and light blue
Map showing the major faults in the Bay Area, with Hayward in medium and light blue
Leonard G.
Lienkaemper explained that the Hayward Fault, which runs under such highly populated cities as Berkeley, Oakland, Hayward, and San Jose, is in the heart of areas that contain large numbers of buildings and infrastructure. He continued by saying:
"But it's not just one fault, it's the whole shopping basket. If you are in the middle of the Bay Area, you are near a whole lot of faults, and I'm concerned about all of them."
The Rodgers Creek Fault runs under the city of Nappa. In August of this year a 6.0 magnitude earthquake struck Nappa during the early morning hours, reportedly injuring 200 people and doing an estimated $600 million in damage to privately, commercial buildings and public infrastructure.
David P. Schwartz, a geologist with the U.S. Geological Survey, said the study's findings is consistent with his belief that pressure built up along the faults could potentially cause multiple large earthquakes, saying "there’s sufficient stress built on these locked patches to allow large quakes to occur now."
Although scientists don't know exactly when a massive earthquake will strike, the area is long overdue. According to Lienkaemper, the fault moves about every 250 years, however the locked area hasn't moved in the last 400 years. He went on to tell Science 20:
"The San Andreas Fault and its two other large branches, the Hayward and Northern Calaveras, have been quiet for decades. This study offers a good reminder to prepare today for the next major earthquake."
More about Earthquake, San Andreas Fault system, Pacific northwest, fault creep, San Francisco
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