San Jose Mercury News
June 12, 1993Scientists to use explosives
in search for faultsOrange County Register
SANTA ANA — Scientists plan to set off up to 60 underground explosions in Southern California that are expected to reveal hidden faults like the one that generated the deadly 1971 San Fernando earthquake.
The explosions will emit waves of energy, some that will bounce off faults and be measured by devices along a blasting zone that extends from the Mohave Desert to the Seal Beach Naval Weapons Station.
The blasts also will provide a clearer picture of the region's geology, enabling scholars to better predict where intense shaking might occur when quakes erupt on faults such as the Newport-Inglewood, part of which snakes through Orange County.
Some of the explosions will occur near the faults but are not expected to trigger earthquakes, scholars said. Similar blasting programs already have revealed faults in the Bay Area and northern Alaska.
"There's no reason for alarm; the blasting we'll do in October will be in isolated spots and won't be felt by most people," said Gary Fuis, a researcher with the U.S. Geologial Survey, which is collaborating with Southern California universities.
The isolated spots include an area off Kitts Highway at Seal Beach Naval Weapons Station, where 1,000 to 2,000 pounds of ammonium nitrate will be exploded in a 180-foot-deep hole in late October.
"The blast will not affect any of our weapons or oil pipelines," said Richard Williamson, a base spokesman.
However, some residents near the northwest edge of the 5,000-acre base might hear a thud when the blast goes off, scholars said.
The date and time of the blast have not been set. But it's expected to occur after 10 p.m. to reduce the chance that seismographs will record the vibration of passing trucks.
The explosion will take place along a 120-mile route that begins near Harper Lake in the Mojave Desert, extends through the San Gabriel Mountains, Azusa and Whittier and ends in Seal Beach.
The amount of explosives used in the blasts will range from 250 pounds to 4,000 pounds. All charges will be set at least 50 feet below the surface.
Fuis said the largest blasts in the $600,000 project will occur in the Mojave Desert and will produce roughly the amount of energy released by a magnitude 2.5 quake.
The explosions will generate primary, or "p," waves, the fastest-moving type of seismic energy, scientists said.
Scientists are able to infer the depth and location of faults largely by how fast these waves bounce off rock formations.
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