Keeping an Eye on Faults in the Valley
The Rubbermaid container sits against a wall on the patio of a Northridge home. It could be an ice cooler.
Only its orange, gray and black electrical wires give it away. They flow up to a rooftop global positioning antenna, revealing an unusual system of quake measurement recently installed throughout the San Fernando Valley.
The container is packed with a 3-foot by 3-foot seismograph, one of 84 that have been placed a kilometer apart in a line from Topanga Canyon to the Mojave Desert.
The seismographs--more than half of them placed in residences--are intended to help scientists identify neighborhoods that will shake most violently during an earthquake. Waves from earthquakes as far as Japan help scientists find hidden faults and measure the depths of underground pockets of sediments. The deeper the pocket, the longer the area above will feel an earthquake.
Scientists from the U.S. Geological Survey and universities such as UCLA, Caltech and USC believe the information they gather will translate into better building standards and earthquake preparation.
The other seismographs are located in national parks and corporate-owned land along a 65-mile line that crosses the Valley.
Scientists plan to add 900 seismographs to the line this fall, planting them on golf courses, schoolyards, shopping centers and football fields as well as other homes to achieve more precise measurements. They will use explosions to trigger waves.
The homeowners who have agreed to take part in the experiment say they have gotten used to having their property serve as laboratories for the $60,000 experiment.
“It just sits there,” said Rick Bierend, a retired police officer who has a seismograph in his Northridge home. “It doesn’t do anything, it doesn’t make any noise. You don’t stumble on it.”
Bierend, whose house sits only a few miles from the site where the Northridge Meadows apartment complex collapsed during the 1994 Northridge earthquake, does not mind the minimal strain on his electric bills. “It’s really just a few cents. It’d be less than a clock radio.”
The experiment, officially known as the Los Angeles Region Seismic Experiment II (LARSE II), is headed by UCLA research scientist Monica Kohler.
LARSE I was begun in 1993 when scientists placed a similar line of seismographs from Seal Beach to the Mojave Desert. Scientists found that beds of sediment in the San Gabriel Valley and Los Angeles basins were deeper than initially believed, but were able to produce only indistinct images of faults.
Kohler and her team of field assistants installed the new seismographs four months ago. They are now collecting recordings from the equipment to create what they compare to a sonogram of hidden faults and deep existing faults.
“Just like we can image the organs inside the body, we can image the faults,” said Gary Fuis, a geophysicist at the U.S. Geological Survey’s Menlo Park field office.
The scientists are hoping that engineers building houses in neighborhoods discovered to be more vulnerable will build houses that can sustain severe shaking. If the experiment results in the discovery of a fault, residents who live in homes above that fault can be warned, Kohler said.
With the Thomas Guide in tow, Kohler’s field assistants began knocking on doors last summer to ask homeowners if they would be willing to serve as hosts of the seismographs.
“At times they were very open. Other times people closed doors and said they weren’t interested,” said field assistant Bryan Kerr, standing in the backyard of the Bierend residence.
Kerr said 40 homeowners in the neighborhood turned him down before Bierend agreed to participate.
Judith Reinsma of Saugus, a school office manager who has had her home since 1982, said she remembers working in her yard one day when a truck with two men drove up cautiously into her driveway.
“They were looking for a place to put these seismology things,” Reinsma said. “They were turned down by four other neighbors, and I thought it was a neat idea.” She signed some permission slips and got a seismograph placed next to her barn.
Mary Artino, 62, of Newhall, had one earthquake memory that made it important for her to say yes: After the 1994 quake, she found that portions of the Antelope Valley and Golden State freeways had collapsed only a few miles from her house.
Every three weeks, the field assistants collect data from Artino’s seismograph, located 20 feet from her house on her horse ranch, and offer her a printout showing the seismic activity beneath her land.
“I ask how things look and they say, ‘Oh, not that much activity,’ and that sounds good to me,” she said.
The data is stored by Incorporated Research Institutions for Seismology Data Management Center, a Seattle company. In a few years, scientists from around the world will be able to access the data online.
Although the plan to add 900 more seismographs to the 65-mile line this fall will improve the quality of data, scientists believe they still need more to properly study the interior of the San Fernando Valley, Fuis said.
He said he is trying to enlist the help of oil companies, which also use the devices.
Once the 900 extra seismographs are added, scientists will begin recording waves triggered by explosions. They will drill eight-inch wide holes, 60 to 80 feet deep, every half-mile. They plan to set off explosions at the bottom of each hole over the span of a few nights.
Although the explosions will take place far from private residences, people in the general area might be able to feel a bit of a shake, Fuis said, adding that the explosions cannot trigger any real earthquakes. Town meetings may be held to explain the process to residents, he said.
The residents who already have seismographs on their land still seem eager to take part in any experiment that might expand their knowledge of earthquakes.
“If they want to leave [the seismograph] here longer, that’s fine too,” Artino said.
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Backyard Quake Watch
As part of a seismology experiment, 84 seismographs--most of them in backyards--have been placed in a line stretching from Topanga Canyon to the Mojave Desert. By recording earthquake waves from the seismographs, scientists can map faults deep beneath the Earth’s surface and measure depths of sediments in the San Fernando Valley basin.
How It Works
1. Seismic sensor buried 2-4 feet deep picks up ground motion and sends electrical signal to data recording system.
2. Data recording system processes and stores ground vibration information on its internal disk, which is later dumped onto an external disk.
3. Global positioning system helps correct time on data recording system’s internal clock. GPS receive picks up accurate time from satellites every hour and sends it to data recorder clock.
4. Scientist picks up disk and downloads onto a computer for analysis.
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1. Seismic sensor
2. Data recorder
External data storage disk
Global positioning system receiver
Rubber tub
3. Satellite
Source: UCLA research scientist Monica Kohler
Researched by JULIE SHEER / Los Angeles Times
