How do the plates move at the San Andreas Fault?
The Pacific Plate (on the west) slides horizontally northwestward relative to the North American Plate (on the east), causing earthquakes along the San Andreas and associated faults. The San Andreas fault is a transform plate boundary, accomodating horizontal relative motions.
How fast does the Pacific Plate move?
~3-4 inches a yearThe Pacific Plate is moving to the northwest at a speed of between 7 and 11 centimeters (cm) or ~3-4 inches a year. The North American plate is moving to the west-southwest at about 2.3 cm (~1 inch) per year driven by the spreading center that created the Atlantic Ocean, the Mid Atlantic Ridge.
What type of plate movement is the San Andreas Fault?
The San Andreas Fault and Queen Charlotte Fault are transform plate boundaries developing where the Pacific Plate moves northward past the North American Plate. The San Andreas Fault is just one of several faults that accommodate the transform motion between the Pacific and North American plates.
How far did the San Andreas Fault slip in 1906?
296 milesThe 1906 earthquake ruptured the northernmost 296 miles (477 km) of the San Andreas Fault between San Juan Bautista and Cape Mendocino. By comparison, the 1989 Loma Prieta earthquake had a rupture length of only 25 miles.
What is the fastest moving plate in the world?
The Pacific Plate is the fastest at over 10 cm/y in some areas, followed by the Australian and Nazca Plates. The North American Plate is one of the slowest, averaging around 1 cm/y in the south up to almost 4 cm/y in the north.
Where are the fastest moving plates?
These average rates of plate separations can range widely. The Arctic Ridge has the slowest rate (less than 2.5 cm/yr), and the East Pacific Rise near Easter Island, in the South Pacific about 3,400 km west of Chile, has the fastest rate (more than 15 cm/yr).
What will happen if the San Andreas Fault breaks?
Narrator: Parts of the San Andreas Fault intersect with 39 gas and oil pipelines. This could rupture high-pressure gas lines, releasing gas into the air and igniting potentially deadly explosions. Stewart: So, if you have natural-gas lines that rupture, that's how you can get fire and explosions.
When was the last time San Andreas Fault moved?
San Andreas FaultStatusActiveEarthquakes1857, 1906 (Mw ≈7.8), 1957 ( Mw 5.7), 1989 ( Mw ≈6.9), 2004TypeTransform faultMovementDextral16 more rows
What is the biggest fault line in the world?
The Ring of Fire is the largest and most active fault line in the world, stretching from New Zealand, all around the east coast of Asia, over to Canada and the USA and all the way down to the southern tip of South America and causes more than 90 percent of the world's earthquakes.
What was the worst earthquake in history?
Also known as the Great Chilean earthquake (Spanish: Gran terremoto de Chile), it was the most powerful earthquake ever recorded. The earthquake hit on May 22 in the afternoon (19:11 GMT, 15:11 local time), approximately 100 miles (160 km) off the coast of Chile, parallel to the city of Valdivia.
How many times has SF burned down?
Between 1849 and 1851, San Francisco was almost entirely destroyed by fire seven times. And each time people rebuilt, they tried more and more high-tech methods to prevent future damage.
What was the worst earthquake in California?
San Francisco earthquake of 1989, also called Loma Prieta earthquake, major earthquake that struck the San Francisco Bay Area, California, U.S., on October 17, 1989, and caused 63 deaths, nearly 3,800 injuries, and an estimated $6 billion in property damage.
How fast is the Pacific plate moving science partnership?
As the Pacific Plate continues to move at a rate of roughly seven centimeters (2.75 inches) per year—about the rate at which fingernails grow—new volcanic material is building up over the Hawaiian hot spot.
How fast are the Hawaiian Islands moving?
Presently the Hawaiian Islands and our part of the Pacific plate are moving northwest at about 100 mm (4 in.) per year, relative to the island-producing hot spot. The trajectory of motion points toward Hokkaido on the northern part of the Japanese Island chain, 6,300 km (3,900 mi) away.
Is the rate that the Pacific plate is moving increasing or decreasing?
No, the rate of movement of the Pacific Plate is based on an average of the plate's movement over time with slight variations from year to year. Currently, that rate of movement is approximately 7 millimeters per year, an extremely slow pace for a tectonic plate.
Is the Pacific plate sinking?
The new calculations showed the Pacific plate is pulling away from the North American plate a little more -- approximately 2 millimeters a year -- than the rigid-plate theory would account for, he said. Overall, the plate is moving northwest about 50 millimeters a year.
How many miles of displacement is there along the San Andreas fault?
Geologists believe that the total accumulated displacement from earthquakes and creep is at least 350 miles along the San Andreas fault since it came into being about 15-20 million years ago.
What is the displacement of a block on the opposite side of the San Andreas fault?
Geologists refer to this type fault displacement as right-lateral strike-slip.
How does offset work in earthquakes?
Total offset accumulates through time in an uneven fashion, primarily by movement on first one, and then another section of the fault. The sections that produce great earthquakes remain "locked" and quiet over a hundred or more years while strain builds up; then, in great lurches, the strain is released, producing great earthquakes. Other stretches of the fault, however, apparently accommodate movement more by constant creep than by sudden offsets that generate great earthquakes. In historical times, these creeping sections have not generated earthquakes of the magnitude seen on the "locked" sections.
How many feet was the road across the head of Tomales Bay?
During the 1906 earthquake in the San Francisco region, roads, fences, and rows of trees and bushes that crossed the fault were offset several yards, and the road across the head of Tomales Bay was offset almost 21 feet, the maximum offset recorded.
What fault is the movement of blocks along?
Movement of blocks along the San Andreas fault.
Does the creeping section of the fault cause earthquakes?
In historical times, these creeping sections have not generated earthquakes of the magnitude seen on the "locked" sections.
What is the San Andreas fault?
The San Andreas Fault marks the junction between the North American and Pacific Plates. The fault is 1300 km long, extends to at least 25 km in depth, and has a north west-south east trend. It is classified as a right lateral (dextral) strike-slip fault.
Why is the Pacific Plate moving west?
The Pacific Plate is being moved north west due to sea floor spreading from the East Pacific Rise (divergent margin) in the Gulf of California. The North American Plate is being pushed west and north west due to sea floor spreading from the Mid Atlantic Ridge (divergent margin).
Which plate is moving north west?
Although both plates are moving in a north westerly direction, the Pacific Plate is moving faster than the North American Plate, so the relative movement of the North American Plate is to the south east. The Pacific Plate is being moved north west due to sea floor spreading from the East Pacific Rise (divergent margin) in the Gulf of California.
What happens when the frictional forces are overcome?
When the frictional forces are overcome, the plates slip suddenly and shallow focus earthquakes are generated. Landscape and manmade features (eg rivers, fences and roads) are displaced across the fault as movement occurs. San Francisco has historically suffered significant earthquakes, notably in 1906 and 1989.
Where does the San Andreas fault run?
The San Andreas fault in CA runs from northern CA down to Mexico. Approximately how fast do the plates move at this fault location?
When one part of a fault ruptures, what happens?
When one part of a fault ruptures (displaces) energy is released from that location and transferred to another part of the fault line.
What is the biggest threat of megathrust earthquakes?
One of the largest threats of megathrust earthquakes where subduction occurs is tsunami waves being produced.
What is the first and most destructive ground shaking seismic wave?
P waves are the first and most destructive groundshaking seismic waves.
What happens to groundwater during an earthquake?
During an earthquake, groundwater can be forced (pumped) to the Earth's surface by ground shaking, causing the soils to become water-saturated and unstable. What is this process called?
Where do earthquakes occur?
Earthquakes occur at all three different types of plate margins.
Where did the 2011 tsunami hit?
The 2011 Japan tsunami wave traveled across the Pacific ocean and reached the west coast of the United States.
Overview
The San Andreas Fault is a continental transform fault that extends roughly 1,200 kilometers (750 mi) through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal). The fault divides into three segments, each with different characteristics and a different degree of earthquake risk. The slip rate along th…
Fault zones
The northern segment of the fault runs from Hollister, through the Santa Cruz Mountains, epicenter of the 1989 Loma Prieta earthquake, then up the San Francisco Peninsula, where it was first identified by Professor Lawson in 1895, then offshore at Daly City near Mussel Rock. This is the approximate location of the epicenter of the 1906 San Francisco earthquake. The fault returns onshore at Bolinas …
Plate boundaries
The Pacific Plate, to the west of the fault, is moving in a northwest direction while the North American Plate to the east is moving toward the southwest, but relatively southeast under the influence of plate tectonics. The rate of slippage averages about 33 to 37 millimeters (1.3 to 1.5 in) a year across California.
The southwestward motion of the North American Plate towards the Pacific is creating compress…
Formation
The San Andreas began to form in the mid Cenozoic about 30 Mya (million years ago). At this time, a spreading center between the Pacific Plate and the Farallon Plate (which is now mostly subducted, with remnants including the Juan de Fuca Plate, Rivera Plate, Cocos Plate, and the Nazca Plate) was beginning to reach the subduction zone off the western coast of North America. As the relative mo…
Study
The fault was first identified in Northern California by UC Berkeley geology professor Andrew Lawson in 1895 and named by him after the Laguna de San Andreas, a small lake which lies in a linear valley formed by the fault just south of San Francisco. Eleven years later, Lawson discovered that the San Andreas Fault stretched southward into southern California after reviewing the effects o…
Earthquakes
The San Andreas Fault has had some notable earthquakes in historic times:
• 1857 Fort Tejon earthquake: About 350 kilometers (220 mi) were ruptured in central and southern California. Though it is known as the Fort Tejon earthquake, the epicenter is thought to have been located far to the north, just south of Parkfield. Two deaths were reported. Its moment magnitude was 7.9.
See also
• California earthquake forecast
• Central Valley (California) – Flat valley that dominates central California
• Coast Range Geomorphic Province
• Garlock Fault – Fault running along the margins of the Mojave Desert of Southern California,United States
Further reading
• Collier, Michael (December 1, 1999). A Land in Motion. UC Press. ISBN 978-0-520-21897-0.
• Stoffer, Philip W. (2005). The San Andreas Fault In The San Francisco Bay Area, California: A Geology Fieldtrip Guidebook To Selected Stops On Public Lands. USGS. General Interest Publication 16.