Underground Blasts for Earthquake Study Planned

Despite some nervousness, Los Angeles officials on Wednesday preliminarily approved a U.S. Geological Survey plan to set off explosives underground in seven city parks in West Los Angeles and the San Fernando Valley to better map earthquake faults.

Scientists say the detonation of explosives at the city-owned sites and 90 other locations around Southern California in October will allow them to gather data that could reduce injuries and property damage in future temblors.

All the sites were chosen to focus on fault systems involved in the 1994 Northridge earthquake, said Tom Burdette, an operations chief for the federal agency. The earthquake caused 72 deaths and $30 billion in damage.

“We need to know more about the fault structure that failed there in that earthquake,” Burdette told the Los Angeles City Council’s Arts, Health and Humanities Committee during an hourlong hearing.

The committee recommended that the City Council approve the permits but set stringent conditions on the underground explosions planned for parks in Pacific Palisades, Reseda, Van Nuys, Chatsworth and Aliso Canyon.

The largest explosions might cause movement equivalent to a magnitude 2 quake, which would be undetectable to most people, Burdette said.

Councilman Mike Feuer, the panel’s chairman, said he had concerns that the detonations might endanger park users, disturb residents or cause sinkholes or other damage.

“I know it is a sensible thing to do from a scientific perspective,” Feuer told Burdette. “The question is from a quality of life perspective is there some degradation we can avoid.”

The committee recommended that the full council, which is to act on the matter within a week or so, require an environmental impact report and a public education campaign before the tests.

Normally, explosives are put in the holes a week in advance, but under the plan approved by the committee Wednesday, the explosives would not be in place until 24 hours before the test and security will be stationed at each site to keep the public away.

The Recreation and Parks Commission also supports the tests in concept but punted the issue to the City Council.

Committee members said the biggest concern is that the underground explosions not trigger a major earthquake.

Burdette said an earthquake has never been generated in 30 years of seismic testing in earthquake zones.

“I can’t say ‘no it can’t happen,’ ” Burdette said. “[But] based upon our experience and the logic of how it is that an earthquake is generated, versus what we are doing, it is impossible, but it’s something you have to accept on faith.”

The explosions are part of the Los Angeles Regional Seismic Experiment, which is being conducted by the U.S. Geological Survey and the Southern California Earthquake Center.

In the first phase in 1994, underground explosions were set off in the San Gabriel Valley and Mojave Desert. Geologists described the results as “sometimes exciting” but said some images were too indistinct.

In the new tests, scientists will drill holes 65 to 100 feet deep, at the bottom of which they will put 50 to 1,000 pounds of ammonium nitrate explosives. During five days of sequenced tests, explosions will be monitored by 1,000 seismographs along the line.

The biggest charge, 1,000 pounds, is proposed for federal property near Hansen Dam. Tests will use 500 pounds each at Chatsworth Park and the Sepulveda Basin in Van Nuys. Smaller charges will be used at Palisades Park, Jessup Park, Chatsworth Reservoir, Van Nuys-Sherman Oaks Park, Reseda Park and Aliso Canyon Park.

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Seismic Mapping Project

The U.S. Geological Survey has received preliminary approval to drill deep holes in seven city parks and set off underground explosions as part of a study of earthquakes. People living near the parks are unlikely to feel any movement, but the blasts would be the equivalent of a magnitude 2 earthquake.