Mapping the San Andreas
Geologist Angel Olguin jams a seismic sensor in a shallow trough scraped in the desert floor near the Salton Sea. This and thousands of other sensors will record seismic waves from detonated explosives to "map" the San Andreas fault and other features of the Earth's crust below. (Don Bartletti / Los Angeles Times)
Reporting from the Salton Sea -- Three days after the earthquake and tsunami devastated northeastern Japan, Gary Fuis walked across the San Andreas fault under a moonlit sky. The desert was quiet. A breeze fanned through the creosote. To the west, he could see the Salton Sea, and to the east, the headlamps of the night crew taking up their positions.


In a little more than an hour, they would start detonating their explosives, generating seismic waves that would be recorded by seismometers buried throughout these sandy hills and positioned on the floor of the Salton Sea.


A geophysicist with the United States Geological Survey, Fuis is overseeing an ambitious project to create an underground image of one of the most seismically active and geologically complex regions of the country, a triangle of land extending from Palm Springs to the Mexico border.


This work, he believes, will change current assumptions about the earthquakes that originate here, especially the Big One expected on the San Andreas fault. For nearly three weeks his teams have worked night and day to cover hundreds of miles and position thousands of instruments.

Fuis, 67, sat on the top of a ridge and took out his dinner, a ham and jalapeno sandwich. From here, he would be able to stay in touch with the crew by two-way radio and cellphone in case any problems or confusion arose during the night.


A voice broke over the radio.


"Train south."


A freight speeding along the shore of the lake would interfere with the readings from the detonations, and they'd have to wait until it passed.


Fuis looked south toward Bombay Beach, a community of small homes and double-wide trailers on the edge of the Salton Sea, where the San Andreas fault begins its jagged 800-mile course toward the Mendocino coast.


Three years ago, seismologists imagined the effect of a magnitude 7.8 earthquake with an epicenter less than a mile from where he sat. Their scenario had the full force of the temblor reaching the L.A. Basin in less than two minutes. The shaking would extend as far north as Ventura.


The released energy would be approximately 30 times less than the Japanese earthquake. Still, landslides, fires, collapsed buildings and roadways, severed communication lines, cracked runways, derailed trains, broken aqueducts and dams were projected, along with nearly 2,000 deaths, 50,000 injuries and $200 billion in damage.


The model was based on the last rupture of the San Andreas in this region, dated more than 300 years ago by recent geological studies. Because this stretch of the fault — from Bombay Beach to the Cajon Pass — has not moved since then, it is considered especially vulnerable to a major earthquake.


Fuis describes the fault with dispassionate conviction. It is "near failure," he says, though he believes the seismologists' predictions may not be accurate. Whether the destruction will be worse or not, he's not certain. He just knows that some conclusions have been drawn without enough information.


"Neither the shape of the San Andreas fault nor the sedimentary basins that the cities have been built upon are well enough understood to provide accurate calculations of the shaking," he said.


The chatter on his radio picked up.


He checked the time — 21:59:07 — less than a minute before the first blast.