Los Angeles set for major earthquake

Los Angeles at risk of major earthquake

22 June 2006

By Jack Doyle

THE city of Los Angeles is at risk from a major earthquake in the near future, according to research published yesterday.

Scientists examining the southern part of the San Andreas fault, which runs to the east of the city, found evidence of a pressure build up, as two continental plates rub against each other.

The researchers used satellite data to measure the amount of movement between the North American and Pacific plates.

They found evidence of substantial movement of the plates, suggesting that pressure may soon be released in an earthquake.

The greater the amount of movement along a fault line, the greater chance of a giant quake.

Professor Fialko, from the Institute of Geophysics and Planetary Physics at the University of California, led the study.

He said: “The observed strain rates confirm that the southern section of the San

Andreas fault may be approaching the end of the interseismic phase of the earthquake cycle.”

A great earthquake has not been recorded in the southern section of the fault for at least 250 years.

In 1906, when the northern section of the fault erupted, around 3,000 people died in San Francisco in an earthquake measuring 7.8 on the Richter scale. In 1857, the central part of the fault erupted, creating the Fort Tejon earthquake, which measured 8.0.

The science of predicting earthquakes is notoriously difficult. Seismologists struggle to judge exactly when and where earthquakes will occur.

Fialko’s research was published by science journal Nature.

© Irish Examiner, 2006, Thomas Crosbie Media, TCH



Los Angeles set for major earthquake


THE southern end of the San Andreas fault near Los Angeles - which has been still for more than two centuries - is under immense stress and could produce a massive earthquake at any moment, a scientist said yesterday.

Professor Yuri Fialko, of the Scripps Institution of Oceanography at La Jolla, California, said given average annual movement rates in other areas of the fault, there could be enough pent-up energy in the southern end to trigger a cataclysmic jolt of up to ten metres or 32ft, far bigger than the earthquake which destroyed San Francisco in 1906. A sudden lateral movement of between seven and ten metres would be among the largest ever recorded.

According to the US Geological Survey (USGS), the 1906 earthquake, which killed between 3,000 and 6,000 people and left up to 300,000 homeless, was produced by a sudden movement of the northern end of the fault of up to 21ft or 6.4m.

Professor Fialko said there had been no recorded movement at the southern end of the fault - the 800-mile long geological meeting point of the Pacific and the North American tectonic plates - since the dawn of European settlement in the area.

"The observed strain rates confirm that the southern section of the San Andreas fault may be approaching the end of the inter-seismic [between earthquakes] phase of the earthquake cycle," he wrote in the science journal Nature.

He said the lack of movement for 250 years correlated with the predicted gaps between major earthquakes at the southern end of the fault of between 200 and 300 years.

Elsewhere on the fault, there were average slippage rates up to a couple of centimetres a year that prevented the build-up of explosive pressure deep underground.

When these became blocked and then suddenly broke free they produced tremors or earthquakes of varying intensity, depending on the movement that had taken place before and for the duration of the blockage.

Prof Fialko said there were three possible explanations for the lack of observed movement in the southern section: creepage under the surface; that it had no external manifestation; and that it simply might not move as much as the rest of a major blockage.

"Except for the first possibility, the continued quiescence increases the likelihood of a future event," he wrote.

Making calculations based on a wide range of land and satellite observations, Prof Fialko discounted the idea of creepage and warned of an impending disaster.

"Regardless of fault geometry and mechanical properties of the ambient crust, results presented in this study lend support to intermediate-term forecasts of a high probability of major earthquakes on the southern San Andreas fault system."

USGS said that the most recent major earthquakes in the north and central zones of the San Andreas fault were in 1857 and 1906.

Prof Fialko cautioned that understanding earthquakes was a complicated subject.

"Although highly accurate and detailed geodetic data provide useful constraints on the rate of build-up of stress and the probability of large events on a given fault, the relationships between loading rate, absolute stress level and the rate of seismicity are still poorly understood," he said.

Last updated: 22-Jun-06 02:21 BST

©2006 Scotsman.com



Southern San Andreas fault waiting to explode

Informant: peter6264


Los Angeles County Getting Ready for the Big One

Los Angeles Times - CA,USA Local officials are making progress in preparing to respond to a catastrophic earthquake or other disaster, but more work is needed, especially at the...



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