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The San Andreas Fault


By Udhay Aman Chopra


Simply put, a fault is a fracture or a gap in the crust of the Earth, these are also visible on the surface of the earth due to the displacement of rocks.

Rocks are very rigid and usually brittle in nature, and due to energy build-up in the crust of the Earth, stress builds up in the rocks and when it exceeds a breaking point, the energy dissipates as the rocks give way.

In the mantle and the crust of the Earth the deformation (due to the stress release) is gradual (since mantle can flow stress release doesn’t affect it so much) whereas in the brittle upper crust it is a fracture (an instantaneous stress release), which causes movement along a fault and is felt by us in the form of an earthquake.

A 40,000 km long highly active horseshoe shaped stretch of volcanoes, active and dormant, has come to be known as the RING OF FIRE!

The Ring of Fire stretches from New Zealand in the South Pacific, stretching up to the Russian Peninsula of Kamchatka crossing over the Bering Strait and then heading down south on the Western seaboard of the Americas to the southern part of Chile. The more than 452 volcanoes on this seismic zone account for around 75% of the world’s active volcanoes. The Ring of Fire or – from my point of view – “Volcano Highway” is the most active and exciting place on earth for the study of earth’s energy release and seismic activity.

The Ring of Fire affects human life on a continuous basis and has been the reason for many of the world’s natural calamities, like the earthquake and tsunami in the Indian Ocean in 2004, in which entire towns were wiped out and close to 300,000 people were killed.

A small but very interesting part of this Ring of Fire is the San Andreas Fault, which stretches from the Pacific Ocean to the inland in California, USA. Amazingly, the Silicon Valley, where the world’s largest IT giants have their headquarters, sits right on the San Andreas Fault. The 1857 Fort Tejon Earthquake (Magnitude ~7.8) which took 3,000 lives and caused fires which raged on for four (4) days and nights are all the famous works of San Andreas Fault.

A stunning aerial picture of the San Andreas fault-line

In 1895 Professor Andrew Lawson first identified the Northern Zone of the Fault and named it after the surrounding San Andreas Valley. Following the 1906 Earthquake in San Francisco he tracked the fault all the way to Southern California.

The fault is divided into three Fault Zones. The Northern, Central and Southern. The fault runs from Hollister, CA to Salton Sea, CA and is offshore and onshore at many points. Many more fault lines which intersect this fault are known as Sister Fault.

The Pacific Plate is to the West of the fault and is moving in a Northwest direction whereas the North American plate to the East of the fault is moving in a Southwest direction.

The fault began to form around the mid-Cenozoic era around 30 million years ago.

The San Andreas Fault Observatory at Depth (SAFOD) opened in 2004. The goal of SAFOD is to drill a hole 3km into the Earth’s crust and The Fault. An array of sensors will be installed to record seismic activities which has helped the geologists to decipher and share with us the secrets hidden below the Earth’s Surface.

Rohil Bahl