The Creeping Imperial FaultSoutheast of the Los Angeles basin and due East from San Diego lies Calif

The Creeping Imperial FaultSoutheast of the Los Angeles basin and due East from San Diego lies California’s Imperial Valley. It is heavily irrigated, as you see from the small irrigation ditch featured in this photo. The land is quite flat and has been filled in with sediment from the Colorado River. Thanks to irrigation channels leading from the Colorado, the area has become a rich area for growing plants and vegetables. But, many unseen geological features lurk beneath the surface of the Imperial Valley. The San Andreas Fault enters the northwestern tip of this Valley, but then breaks off into a couple different segments along the coastline of the Salton Sea. South of the Salton Sea, the fault reorganizes into a system that travels into Mexico known as the Imperial Fault.In this photo of what appears to be a simple Imperial Valley irrigation ditch, you’ll notice that the concrete has cracked and there are plants growing through the concrete along these fractures.This irrigation ditch sits directly atop of the Imperial Fault. This picture was taken from the “North American” plate side of the fault, looking across at the Pacific plate, so the land to the top of this image is moving to the right relative to the viewer (the San Andreas system being a right-lateral fault).The fault hasn’t had a major earthquake since a magnitude 6.4 event in 1979, which happened before this channel was built, but it’s still there and still slowly creeping. Concrete doesn’t handle shear stress very well, so here it’s cracking due to that slow motion. The Fault hasn’t had large motions since 1979, but it still creeps along, allowing very subtle motions to take place while the stress builds up that will eventually drive a larger earthquake.This fault also offsets a nearby rail line and telephone poles, some of which were built before the 1979 quake and are offset by a meter or more. There is also, for some reason, a buried high pressure gas line at this location.-JBBImage credit: Me, image owned by the author of this post.1979 Earthquake details:http://www.data.scec.org/significant/imperial.html -- source link

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