The Sand Andreas Fault lies at the boundary of two different tectonic plates. While it is California's sleeping giant, it actually accounts for the strongest earthquakes in the state.
The San Andreas Fault
When the San Andreas Fault is viewed from space, it appears like a narrow and long valley that marks the meeting of the Pacific plate and the North American plate. This break between the two different plates is known as a fault.
However, when examined from a close distance, there are actually several faults and fractures that mark the exact zone where the two different plates slide against each other. At times, this boundary contains several other smaller faults that could break when an earthquake happens.
It was in 1895 that the San Andreas fault was discovered by Professor Andrew Lawson, who was from the University of California. Professor Lawson discovered it in the San Andreas Valley and decided to name it after the location.
The fault stretches roughly 800 miles across California. It lies at the tectonic boundary between the North American and Pacific plates.
Segments of the San Andreas Fault
The San Andreas Fault has three primary segments, namely, the southern, central, and northern parts. Each specific segment has its own characteristics and earthquake risk degree.
The Northern Segment runs from Hollister all the way to the San Francisco Peninsula. It passes through the Santa Cruz Mountains. It continues offshore, close to Fort Ross, and returns to shore to form a linear valley that the Gualala River flows through. It then goes offshore again at Point Arena and terminates at the Mendocino Triple Junction, close to Eureka.
The Central Segment has a northwestern trajectory, running from Parkfield to Hollister. This Central Segment experiences an odd phenomenon called aseismic creep, wherein the fault keeps on slipping without triggering any noticeable seismic activity, despite the frequent occurrence of earthquakes.
The last portion, the Southern Segment, starts close to California's Bombay Beach and stretches towards the south. It streaks through the Cajon Pass as it gears to the northwest. This Southern Segment is capable of triggering intense disruptions that could trigger quakes with a magnitude of 8.1. This could result in tragic losses in crucial areas, such as Riverside, San Bernardino, and Los Angeles.
How Did the Fault Form?
The birth of the San Andreas Fault goes back roughly 30 million years ago in California. This was when the North America plate and the Pacific plate had their first encounter.
Prior to this, a different oceanic plate known as the Farallon plate was disappearing underneath the subduction zone of North America. With the new configuration, the two plates ended up sliding past each other rather than crashing into one another. This boundary is known as a strike-slip fault.
The Southern Segment of the fault specifically started shaping roughly five million years after the fault was formed. At first, the system consisted of the fault zone of Clemens Well-Fenner-San Francisquito, which existed roughly 13 to 22 million years ago. As time passed, the system evolved.
The fault's evolution, especially in its Southern Segment, has been affected by factors like between-plate motion vector differences and the "Big Bend."
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