Underground Blasts to Help Map Fault Lines

Twenty-five small tremors shook outlying Los Angeles areas early Wednesday, including near this remote town in the Angeles National Forest, but don’t blame Mother Nature.

The mini-quakes were artificially induced in the name of science, and if you live in selected parts of the San Fernando Valley and the Westside, they will be coming this weekend to a neighborhood near you.

The research project that began Wednesday morning after two years of planning is called the Los Angeles Region Seismic Experiment, or LARSE. It aims to set off a total of 93 underground explosions and use the resulting shock waves to produce a detailed map of earthquake faults from the Pacific Palisades northward into the Mojave Desert.

The blasts generated by the project, sponsored by the U.S. Geological Survey and the Southern California Earthquake Center, are to continue Thursday and Friday mornings in sparsely populated areas of the desert and Topanga State Park.

In those remote areas, project organizers said, only a handful of people are likely to feel or hear the explosions.

But when the project moves into earthquake-anxious Los Angeles Sunday morning, a few nerves might be rattled. Blasts are scheduled along a line stretching from an area half a mile from the beach in the Palisades into the Santa Monica Mountains and through the Valley.

The sites include the grounds of Riviera Country Club, the Veterans Administration Hospital in West Los Angeles, Granada Hills High School and Cal State Northridge.

While the remote-region blasts are produced by as much as 4,000 pounds of ammonium nitrate explosives apiece, the blasts scheduled for populated areas will be far milder in hopes of allaying concerns.

“We’ll be using only about 10 to 25 pounds of explosives for areas with dense population,” said Mark Benthien, spokesman for the Geological Survey, standing in a former Marshalls discount store in Reseda that the project is using for its headquarters. “You would have to be living very nearby to hear them at all.”

He said the blasts, which are all a minimum of 60 feet underground, cannot set off real earthquakes. This type of testing has been done for 30 years, project officials said.

The majority of blast sites are on government-owned property. The Los Angeles City Council gave its permission in July for testing on its property--including Van Nuys-Sherman Oaks Park and Reseda Park--with the provision that security guards be posted at the sites once the explosives are in place.

The holes for the city sites were drilled during the past several weeks, Benthien said. The explosives will not be placed in them until Saturday, less than 24 hours before the blasts are to take place.

Some blast sites are on private land. Most property owners approached by project officials gave their permission, Benthien said, even though they are not being paid.

“They realized the scientific testing to be gained by the project is important,” Benthien said.

But some developers, including the giant Newhall Land & Farming Co., refused to allow blasts on their property.

“Following the 1994 earthquake, we let [the Geological Survey] on the land for a couple of years, off and on, to do a lot of trenching and follow-up work,” said Marlee Lauffer, a Newhall Land spokeswoman. “We got to the point where it was interruptive to our ranching and farming operations.”

On each day of testing, the blasts take place for several minutes beginning at 1:30 a.m., 3 a.m. and 4 a.m. The early morning times were chosen to minimize the chance that vibrations from industrial, construction or traffic activity would pollute the data picked up by the more than 1,400 seismic monitors set out for the project.

The blasts end with the city tests on Sunday, and then scientists at seismic centers in the United States and Europe will begin to process the data.

“It will take about a year for them to go through everything and map the faults,” Benthien said.

Total cost for the project, he said, was about $600,000, mostly supplied through government grants. Many of the 110 people who prepared the blast sites and set out the monitors were volunteers.

They are dispatched in teams of two to each site to set off blasts on a precise schedule. Shortly after midnight on Wednesday, retired Geological Survey electronic technician Ron Kaderabek, 69, and recent geology college graduate Luke Reusser, 23, drove down a dirt road in a rented Mercury Mountaineer to get to a site near the small desert town of Lake Hughes in the Angeles National Forest. Unpacking their electronic equipment, they were a study in contrasts.

Kaderabek, wearing a baseball cap from the Oddfellows lodge of which he is president in San Jose, is an old hand at blast tests.

“I’ve done so many, I don’t think I could count them all,” he said going about his work.

It was a first, however, for the long-haired Reusser, who had a couple of earrings in one ear.

“This is exciting,” he said with a wide grin.

When Kaderabek set up a portable unit called the “USGS Blaster,” Reusser turned to him and said, “You are the master blaster!” and both laughed.

Under a star-filled sky, they let out a spool of electric wire to the bore hole about 50 yards away. They unlocked its metal cap, hooked up the wires, replaced the cap and put a couple of bags of dirt overtop to help deaden the blast sound.

Returning to their vehicle, they hooked an electronic clock that had been set earlier in project headquarters into the “Blaster.” At 1:36 a.m., Kaderabek hit the switches to arm the charge, and it automatically went off at exactly 1:37 a.m.

The sound was similar to that of a sonic boom and the ground briefly shook. Then came the hiss of steam rising out of the bore hole from deep in the ground.

“Pretty good one,” said Kaderabek, nodding.

Reusser was looking out into the darkness toward the blast.

“All this preparation comes down to one little second,” he said, “and it worked.”