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.