Seismologist Lucy Jones stands on top of the San Andreas fault, which has pushed up the left side of the hill northward and higher than the side to the right from past earthquakes. (Photo by Allen J. Schaben / Annotation by Raoul Ranoa / Los Angeles Times)
Seismologist Lucy Jones stands on top of the San Andreas fault, which has pushed up the left side of the hill northward and higher than the side to the right from past earthquakes. (Photo by Allen J. Schaben / Annotation by Raoul Ranoa / Los Angeles Times)

As Interstate 10 snakes through the mountains and toward the golf courses, housing tracts and resorts of the Coachella Valley, it crosses the dusty slopes of the San Gorgonio Pass.

The pass is best known for the spinning wind turbines that line it. But for geologists, the narrow desert canyon is something of a canary in the coal mine for what they expect will be a major earthquake coming from the San Andreas fault.

The pass sits at a key geological point, separating the low desert from the Inland Empire, and, beyond that, the Los Angeles Basin.

Through it runs an essential aqueduct that feeds Southern California water from the Colorado River as well as vital transportation links. It’s also the path for crucial power transmission lines.

California earthquake experts believe what happens at the San Gorgonio Pass during a major rupture of the San Andreas fault could have wide-ranging implications for the region and beyond.

They worry a huge quake could sever lifelines at the pass for weeks or months, cutting Southern California off from major highway and rail routes as well as sources of power, oil and gas. Southern California’s cities are surrounded by mountains, making access through narrow passes like the San Gorgonio essential.

Experts have also expressed grave concerns about the Cajon Pass, where Interstate 15 and key electric and fuel lines run. Other problem spots are the Tejon Pass, through which Interstate 5 passes, and the Palmdale area, through which the California Aqueduct crosses.

One of the most dire scenarios geologists have studied is a quake that begins at the Salton Sea. Such a quake would be particularly dangerous because the fault’s shape points shaking energy toward Los Angeles.

Southern California has not seen an earthquake like this since humans started recording history here. But the geological evidence of such quakes is all around us.

Signs of megaquakes

In Desert Hot Springs, hints of the mighty San Andreas fault lie all over: The rise of mountains that created the Coachella Valley. The oases and palm trees — made possible only because earthquakes pulverized rocks that allowed springs to burst to the surface.

A geologist’s trained eye can even spot exactly where the fault is located. In one exposed cliff, USGS research geologist Kate Scharer showed how one side of a hill has moved northward and skyward compared with the right side — and the gouge in the hillside between them was the fault.

Farther away, Scharer described how an old lower canyon was severed from the upper canyon and its ancient source of water.

Click here to continue reading…

SOURCE:  
The Los Angeles Times

Advertisements