"Talk about bad luck!" says Caltech geologist Brian Wernicke, squinting through a telescopic eyepiece at an aerial photo of Landers, California, a small town in the middle of the Mojave desert. "Wham! Right through this house. Wham! Right through that house. The funny thing is, there aren't that many houses out here."
In more ways than one, the earthquake that rumbled through this desolate region on June 28 was an ominous force. In a few fearsome seconds, it rerouted roads, realigned parking lots and reconfigured the landscape in countless capricious ways, miraculously taking only one life. Rather than rupture a single fault line, it swiped a 70-km (45-mile) diagonal slash through several, at one point heaving up a raw ridge of rock roughly the size and shape of a stegosaurus' spine.
For weeks afterward -- even this past week -- the region has been rocked by thousands of nerve-racking aftershocks, and the quake ignited mysterious swarms of smaller earthquakes in volcanic zones hundreds of kilometers away. But most alarming of all, this quake, the largest to hit Southern California in 40 years, appears to have substantially altered subterranean stress fields. In the process, it may have awakened a fitfully sleeping dragon -- the mighty San Andreas, the nation's biggest and most dangerous fault.
With a mixture of excitement and dread, scientists with the U.S. Geological Survey in Pasadena are rushing to augment an already extensive seismic network with portable instrumentation. "Before the San Andreas goes," reflects geologist Ken Hudnut somberly, "maybe we'll catch a precursor." A hot wind swoops across the desert as Hudnut retrieves a plastic box from under an oleander bush and pops the lid to reveal the small satellite receiver it shields from blowing sand. Nearby, a tripod-mounted antenna straddles a survey pipe like a spindly sentinel. Coded signals beamed down by orbiting ! satellites, Hudnut explains, serve to pinpoint the location of the pipe. The slightest shift in the pipe's position, and Hudnut will know the earth around it is on the move.
The southernmost section of the San Andreas has made scientists jumpy for some time now. Between 1948 and 1986, the region adjacent to the fault experienced only one earthquake of magnitude 5.8 or higher.* Since then there have been seven, including the Landers quake, which weighed in at an impressive 7.5. Moreover, this surge in seismicity appears to be occurring on a worrisome schedule. Excavations of old lake-bed sediments by Caltech paleoseismologist Kerry Sieh in the mid-1980s indicate that large earthquakes have roared through this section of the San Andreas at not quite 300-year intervals. The last such quake took place circa 1680. "It's just a gut feeling," ventures Sieh, who is 41 years old, "but I think I'll witness a great earthquake on the southern San Andreas in my lifetime."