Tag Archives: San Andreas Fault

Ancient quakes may point to sinking risk for part of California coast

The city of Long Beach is seen at dusk, California, U.S., September 8, 201

By Tom James

SEATTLE (Reuters) – The Big One may be overdue to hit California but scientists near Los Angeles have found a new risk for the area during a major earthquake: abrupt sinking of land, potentially below sea level.

The last known major quake on the San Andreas fault occurred in 1857, but three quakes over the last 2,000 years on nearby faults made ground just outside Los Angeles city limits sink as much as three feet, according to a study published Monday in the journal Scientific Reports.

Seismologists estimate the 800 mile-long San Andreas, which runs most of the length of the state, should see a large quake roughly every 150 years.

Scientists from California State University Fullerton and the United States Geological Survey found evidence the older quakes caused part of the coastline south of Long Beach to drop by one-and-a-half to three feet.

Today that could result in the area ending up at or below sea level, said Cal State Fullerton professor Matt Kirby, who worked with the paper’s lead author, graduate student Robert Leeper.

“It’s something that would happen relatively instantaneously,” Kirby said. “Probably today if it happened, you would see seawater rushing in.”

The study was limited to a roughly two-square-mile area inside the Seal Beach National Wildlife Refuge, near the Newport-Inglewood and Rose Canyon faults. Kirby acknowledged that the exact frequency of events on the faults is unclear, as is the risk that another quake will occur in the near future.

The smallest of the historic earthquakes was likely more intense than the strongest on record in the area, the magnitude 6.3 Long Beach earthquake of 1933, which killed 120 people and caused the inflation-adjusted equivalent of nearly a billion dollars in damage.

Today, the survey site is sandwiched by the cities of Huntington Beach and Long Beach, home to over 600,000 people, while nearby Los Angeles County has a population of 10 million.

Seismologist John Vidale, head of the University of Washington-based Pacific Northwest Seismic Network, said after reviewing the study he was skeptical such powerful quakes could occur very frequently in the area.

Kirby noted that the team could only collect soil core samples within the relatively undisturbed refuge, and that taking deeper samples would shed light on the seismic record even further back, potentially giving scientists more examples of similar quakes to work from.

(The story was refiled to correct the second paragraph to clarify timing of last known major quake on the San Andreas fault)

(Reporting by Tom James; Editing by Patrick Enright and James Dalgleish)

Minor Quake Strikes Oakland Area

Some residents of the Easy Bay area didn’t need their alarm clocks to start the week as a magnitude 4.0 earthquake struck the area early Monday morning.

The U.S. Geological Survey (USGS) reported the quake struck at 6:49 a.m., three miles away from Oakland, California.  The quake was felt throughout the Oakland/San Francisco area.

Oakland police Lt. Chris Bolton reported on the department’s official Twitter feed that they had no reports of injuries or damage from the quake.

The quake struck along the Hayward fault, a major fault that remains a concern for geologists in the area.  The scientists believe that the fault could produce a potentially catastrophic quake that could kill tens of thousands.  The Hayward fault is part of the San Andreas fault system.

The fault runs for more than 60 miles through the region from Fremont to Hayward.  The fault runs under hospitals, freeways and reservoirs.  It even runs from end zone to end zone at the football stadium for the University of California Berkeley.

The quake was followed by six aftershocks.

California Prepares for the Next Big Earthquake

Scientists are admitting the likelihood of a massive earthquake along the San Andreas Fault is higher than previous predictions.

The Third Uniform California Earthquake Rupture Forecast, released in March, states that newly discovered fault zones could see a quake jumping between them.  The cascading quake could reach an earthquake of 8.0 or greater.

The odds of a mega-quake increased from 4.7 percent to 7 percent.

The report also said that the odds of a medium level quake has decreased along the lines of the increase of a massive quake.

The southern section of the San Andreas Fault has not seen a massive earthquake in almost 300 years.  The last major quake along the fault took place in 1989 near Santa Cruz, California during Game 3 of the 1989 World Series.   63 people died in that earthquake.  The state’s last major quake overall was the 1994 Northridge quake along a previously undiscovered fault line that left 57 dead and 5,000 injured.

California’s Insurance Commissioner Dave Jones says that he worries about the next “big one.”

“If you ask me what keeps me awake at night, it’s the strong likelihood of a large earthquake,” he said.

Amazingly, despite the fact the state is hit with 1,000 earthquakes a year (most of very small magnitude), only 11 percent of homeowners and renters in the state have earthquake insurance.  Only a comparable number of businesses have insurance.

“It has been 21 years since the last major earthquake in the state and many rationalise that they can do without,” Robert Hartwig of the Insurance Information Institute said.  “Unfortunately, too many seem willing to play Russian roulette with what is likely to be their most valuable asset, their home.”

Earthquake Could Cut Off L.A.’s Water Supply

Los Angeles is one earthquake away from losing a major part of their water supply.

The city of Los Angeles gets almost 90 percent of its water from three major aqueducts.  These aqueducts run from the Colorado River, Owens Valley and the Sacramento-San Joaquin River Delta.

The aqueducts cross the well-known San Andreas Fault a total of 32 times.

This means any major quake along that fault line could end the water supply into the nation’s second largest city.

Mayor Eric Garcetti is calling on city officials to create better plans to protect the city’s water supply.

“[Water is] one of L.A.’s greatest earthquake vulnerabilities,” Garcetti told the L.A. Times. “If it were to take six months to get our water system back … residents and businesses would be forced to relocate for so long that they might never come back.”

Officials are looking to San Francisco’s Public Utilities Commission for a possible solution.  The SFPUC recently installed a specially designed pipe over a fault line that has “accordion-like joints” that would allow the pipe to flex and move in any direction should the fault line move.

“We’re the first city that’s really bet its life on outside water,” U.S. Geological Survey seismologist Lucy Jones told the Times. “We have to cross the faults. There’s no way to not go over the fault.”

“There should be a serious dialogue among the agencies that are responsible for the three sources of water to Southern California,” said Thomas O’Rourke, a Cornell University engineering professor. “Sometimes it’s very difficult to go beyond those institutional barriers…. Somebody just has to take it up.”

Experts: Bigger Quake On Lesser Known Fault Big Problem

Californians have been keeping an eye on the San Andreas Fault for years fearing a “big one” would strike and cause massive damage.

Now, scientists say that a quake of 7.5 or bigger on a lesser known fault might be even more catastrophic than a quake along the San Andreas Fault line.

The Puente Hills thrust fault, which was the fault which brought Friday night’s 5.1 magnitude quake, runs from northern Orange County through downtown Los Angeles and all the way into Hollywood.  The San Andreas Fault runs along the outskirts of Southern California’s metro areas.

Thus, scientists say, a massive quake along the Puente Hills fault would cause significantly more damage and likely brings hundreds or thousands of deaths.  One estimate from the U.S. Geological Survey estimated as many as 1,800 deaths and $250 billion in damage.

The same fault in 1987 had a 5.9 quake that killed eight people and caused $350 million in damage.

One USGS staffer said that a 7.5 quake centered in Los Angeles would be so intense that it would throw heavy objects like a grand piano into the air.

Ocean Waves Help Predict Major Earthquakes

Scientists at Stanford University and MIT have found a new way to predict earthquakes and possible damage in areas where seismologists have struggled with oceans causing small seismic waves.

The scientists have developed a way to use ocean waves as a model for earthquakes and its impact on different types of soil.

The study says that Los Angeles is very vulnerable to a large quake from the San Andreas Fault.

The study shows that because the city sits on what’s called a ”sedimentary basin” shock waves from quakes could be magnified as much as three times their usual level.  A sedimentary basin is softer, sandier dirt surrounded by a ring of rock.  The waves would bounce off the rock and increase in magnitude.

One member of the scientific team said it was similar to a large bathtub full of water.  If you shake the tub, the tub does not shake much but the water within violently shakes along with anything on top of it.

The study says the new system will allow scientists to test the impact of an earthquake on buildings in areas that have not experienced an earthquake for many years.