In 1953, geologist Thomas Dibblee concluded that hundreds of miles of lateral movement could occur along the fault.Īn NSF funded project called the San Andreas Fault Observatory at Depth (SAFOD) near Parkfield, California, involved drilling through the fault from 2004 to 2007. Following the 1906 San Francisco earthquake, Lawson also concluded that the fault extended all the way into Southern California. However, according to some of his reports from 18, he actually named it after the surrounding San Andreas Valley. A common misconception is that Lawson named the fault after this lake. The lake was created from an extensional step over in the fault, which created a natural depression where water could settle. This line ran through San Andreas Lake, a sag pond. He concluded that the fault must have been the origin of the earthquake. When the location of these offsets were plotted on a map, he noted that they made a near perfect line on top of the fault he previously discovered. He began by surveying and mapping offsets (such as fences or roads that had been sliced in half) along surface ruptures. In the wake of the 1906 San Francisco earthquake, Lawson was tasked with deciphering the origin of the earthquake. The fault was first identified in 1895 by Professor Andrew Lawson of UC Berkeley. Sediment deposited by the Colorado River is preventing the trough from being filled in with sea water from the gulf. In this region (known as the Salton Trough), the plate boundary has been rifting and pulling apart, creating a new mid-ocean ridge that is an extension of the Gulf of California. Here, the plate motion is being reorganized from right-lateral to divergent. In the south, the fault terminates near Bombay Beach, California in the Salton Sea. It has been hypothesized that a major earthquake along the subduction zone could rupture the San Andreas Fault and vice versa. In the north, the fault terminates offshore near Eureka, California at the Mendocino Triple Junction, where three tectonic plates meet. The average slip rate along the entire fault ranges from 20 to 35 mm (0.79 to 1.38 in) per year. Traditionally, for scientific purposes, the fault has been classified into three main segments (northern, central, and southern), each with different characteristics and a different degree of earthquake risk. It forms the tectonic boundary between the Pacific Plate and the North American Plate. The San Andreas Fault is a continental right-lateral strike-slip transform fault that extends roughly 1,200 kilometers (750 mi) through the Californias. Plaque showing location of San Andreas Fault in San Mateo County San Francisco, San Bernardino, San Juan BautistaĬalaveras, Hayward, Elsinore, Imperial, Laguna Salada, San Jacintoġ857, 1906 ( M w ≈7.8), 1957 ( M w 5.7), 1989 ( M w ≈6.9), 2004 Arrows show relative motion of the North American Plate (southeastward) and the Pacific Plate (northwestward)ģ5☀7′N 119☃9′W / 35.117°N 119.650°W / 35.117 -119.650

Transform boundary examples