The San Andreas Fault from Above

The name of the San Andreas Fault precedes itself like, well, an immense and unavoidable rift in the earth’s surface. Running some 1,300 kilometres through the US state of California and reaching a depth of 15 to 20 kilometres, the San Andreas forms the tectonic boundary between the Pacific and North American Plates. Yet because of its vast size, it’s difficult to grasp this giant geological feature; except, that is, when you look at it from above.


Image: USGS

The reason the San Andreas Fault is so famous – or perhaps infamous – is because of the major earthquakes for which it has been responsible. Names like the great 1906 San Francisco Earthquake, which left 3,000 dead, or 1989’s Loma Prieta earthquake, which killed 63, leave some trembling at the thought of the next big one. Worrying, a study suggests that the fault is set for just such a super quake of magnitude 7.0 or over, with the risk rising faster than was previously believed.


Image: NASA

View along the fault where it cuts along the base of the Temblor Mountains.

The San Andreas fault’s momentous historic earthquakes have together caused hundreds of kilometres of breaks in the earth’s surface. One of the longest and most active faults in North America, the San Andreas was nevertheless only identified in 1895 by Berkeley geology professor Andrew Lawson. After the fateful 1906 San Francisco earthquake, it was Lawson too who realised that the fault extended into Southern California through locations like the magnificent Carrizo Plain.

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Breathtaking views: Carrizo Plain southeast along the San Andreas Fault.

This beautiful aerial shot shows the San Andreas Fault advancing southeast through the Carrizo Plain. In the foreground, the block on the west side of the fault, right, has been raised up due to plate movement, damming the drainage of water running down from the hills to the east, left.

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Autumnal hues: Northwest along the fault line.

This equally majestic photograph, rich in the colours of Fall and shot from greater distance, shows a northwest view of the San Andreas in the Carrizo Plain. Notice how the upraised block of land on the right eventually gives way to the upraised block on the left in the distance.

Deep erosion in the valley: San Andreas Fault, Carrizo Plain.

This pastel-coloured shot is a southwest view that depicts a deeply eroded valley along the San Andreas. The downstream segment of the channel on the far west side of the fault has been displaced a kilometre or more from the upstream segment, which is out of view to the left.

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Image: Ikluft

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An incredible image showing an aerial view of the San Andreas Fault as it cuts through the Carrizo Plain, photographed from an altitude of 8500 feet.

A historical perspective: View south along the scarp.

In this aerial view of San Luis Obispo County from 1965, the Carrizo Plain lies to the right of the Elkhorn Scarp and Elkhorn Plain to left. A scarp is defined as land displaced by movement along a fault, and the Elkhorn Scarp defines the trace of the San Andreas Fault along much of its length through these plains.

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Thrown off course: Stream offset by the San Andreas Fault.

Another aerial shot from the vaults of 1965, this photo shows that running water is no match for a 20 million year-old fault: a stream has been offset by a quarter of a mile by the fault as it travels through Carrizo Plain. Practically all the images collected here show the San Andreas on its journey through the Carrizo Plain, a long, treeless expanse in which much of the fault line is plainly visible.

Yet Carrizo Plain is just one section of the Southern segment of the San Andreas, which bends south and east past the San Gabriel and San Bernardino mountains as far as the Salton Sea lake in the Colorado Desert. The Central segment stretches northwest between the towns of Parkfield and Hollister. The Northern segment, meanwhile, runs through the Santa Cruz Mountains, on up the San Francisco Peninsula, heading offshore at Mussel Rock, before returning onshore once more at Fort Ross – only to go offshore again for some distance before it terminates. Phew.


Image: NASA

San Andreas from space: The fault line at Palmdale, CA.

This image from space gives an even greater sense of the scale of the San Andreas, visible as the prominent line passing straight through the centre of the picture. The Pacific plate on the left is slowly moving away while the North American Plate is moving towards us in what is known a right lateral strike-slip fault, the movement of which is horizontal.

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Another space perspective: The San Andreas

The clearly marked feature running down the middle of this impressive view is the San Andreas once again. This segment of the fault lies west of the city of Palmdale, about 100 kilometres northwest of Los Angeles. Two large mountain ranges are in shot, the San Gabriel Mountains on the left and the Tehachapi Mountains in the upper right. Another fault, the Garlock, lies at the base of the Tehachapis.

Mission: Shuttle radar topography

Like the other images from space included here, this image was created using data from NASA’s Shuttle Radar Topograpy Mission (SRTM), which is being used by geologists to study fault dynamics and physical features in the land that result from shifting plate tectonics. Quail Lake Reservoir sits in the depression created by past movement along the fault.

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Psychedelic spectacle: The fault along the southwestern edge of the Mojave.

This last topographic image colourfully displays the fault line 75 kilometres north of downtown LA. The whole segment of the fault line shown here last ruptured during the Fort Tejon earthquake of 1857. One of the largest recorded earthquakes in the US, it left an amazing 350 km surface rupture scar along the San Andreas. Were the Fort Tejon shock to occur today, the results could be catastrophic.

The beauty of these images belie the tremendously powerful and destructive force the San Andreas could unleash if it but slipped.

Sources: 1, 2, 3, 4, 5

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