Wednesday, April 28, 2010

[californiadisasters] New map shows active quake faults in O.C.

New map shows active quake faults in O.C.

April 28th, 2010, 7:42 am by Pat Brennan, O.C. Register science, environment editor

The state's first new map of earthquake faults in 16 years shows active faults in Orange County — among them the Newport-Inglewood fault, one of the most dangerous according to the state's geologist.

"That's a very dangerous fault," said John Parrish, head of the California Geological Survey. "In 1933 that was the fault that moved and destroyed Long Beach and killed 120 people. It knocked down all the schools in the Long Beach area."

The map also shows the relationship between another dangerous fault, the Elsinore fault that runs along the Santa Ana Mountains close to Orange County, and the Laguna Salada fault, involved in the recent 7.2 quake in northern Mexico and the thousands of aftershocks that followed.

"We really believe that there's a lot of activity going on on the Laguna Salada fault, creating stresses on the Elsinore fault," Parrish said. "And we're getting those stresses relieved by a number of earthquakes on the Elsinore fault."

The color-coded map outlines faults from black to red. The closer to red, the more recently the fault has been active.

Most of the Newport-Inglewood fault, for example, which runs along the Orange County coast, is highlighted in orange, meaning it has moved sometime in the past 11,000 years — not long in terms of geologic time.

The Elsinore fault also is marked in orange. But parts of it and Newport Inglewood are marked in red, meaning they were active within the past 200 years.

The fault maps are used by policymakers, planners, geologists, the mineral industry and even the insurance industry, Parrish said.

A big innovation since the last map in 1994: this will be the first fully digital version.

Check back for more details on the mapping of faults in Orange County.


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