A San Andreas fault mystery

LOS ANGELES – The San Andreas fault begins its dangerous dance through California at the Salton Sea, at a spot that seismologists long have feared could be the epicenter of a massive earthquake.

But in recent months, this desolate location where the North American and Pacific plates rub together has become the focus of intense interest for a type of movement that is less the Big One than the Slow One.

A muddy spring mysteriously has begun to move at a faster pace through dry earth – first 60 feet over a few months, and then 60 feet in a single day, according to Imperial County officials.

There’s no evidence suggesting this is an immediate precursor to a large earthquake, said U.S. Geological Survey geophysicist Ken Hudnut, who visited the moving spring in July. In fact, the area has been seismically quiet in recent months, with relatively few earthquakes.

Hudnut and other experts stress the movement is not seismic activity. But it’s occurring partly as a result of historic earthquake activity that caused cracks, allowing gases produced deep underground to reach the earth’s surface.

The biggest worry is that the slow-moving scientific mystery could become destructive in other ways.

In its path are Union Pacific freight railroad tracks that connect the Imperial Valley to Yuma, Ariz.; a petroleum pipeline owned by Kinder Morgan, one of North America’s largest energy companies; a stretch of fiber optic telecommunications lines owned by Verizon; and a portion of Highway 111, a major roadway connecting Interstate 10 in the Coachella Valley to the Californiamexico border.

“It’s a slow-moving disaster,” said Alfredo Estrada, Imperial County’s fire chief and emergency services coordinator.

Imperial County declared an emergency this summer, enabling officials to expedite efforts to prevent damage and perhaps even to stop the movement of the spring from getting closer to the railroad tracks.

So far, they haven’t worked.

Officials have been trying to drain water from the moving spring. Union Pacific built a 100-foot long wall of large boulders and steel more than 75 feet deep in the earth in an effort to protect the railroad.