What kind of boundary is the san andreas fault

A mile km long creeping section exists on the central portion of the San Andreas between the and ruptures. The San Andreas fault southeast of San Bernardino has not experienced a major earthquake in the historical record, and paleoseismic investigations of this reach of the fault suggests it last ruptured in the late 17th Century. North of Cape Mendocino, the San Andreas fault merges with the plate boundary of the Cascadia subduction zone that lies offshore of northernmost California, Oregon, and Washington.

We know from paleoseismic investigations in Washington and Oregon and tsunami records in Japan, a magnitude 9 earthquake ruptured the Cascadia subduction zone in Although many Bay Area residents remember the Loma Prieta as the "big one", it pales in comparison to these earlier fault ruptures.

Real-time Earthquakes. Photograph copyright by David Lynch. Click to enlarge. The plates are slowly moving past one another at a couple of inches a year - about the same rate that your fingernails grow. But this is not a steady motion, it is the average motion. For years the plates will be locked with no movement at all as they push against one another. Suddenly the built-up strain breaks the rock along the fault, and the plates slip a few feet all at once.

The breaking rock sends out waves in all directions, and it is the waves that we feel as earthquakes. In San Bernardino and Los Angeles Counties, many of the roads along the fault cut through great mountains of gouge, the powdery, crumbled rock that has been pulverized by the moving plates. The hallmark of the San Andreas Fault is the different rocks on either side of it.

Being about 28 million years old, rocks from great distances have been juxtaposed against rocks from very different locations and origins. The Salinian block of granite in central and northern California originated in Southern California, and some even say northern Mexico.

Pinnacles National Monument in Monterey County is only half of a volcanic complex, the other part being miles southeast in Los Angeles County and known as the Neenach Volcanics. Offset Drainage: Aerial photo of the San Andreas Fault showing drainage that is offset by movement of the fault.

There are many myths and legends about the San Andreas Fault, the biggest being that it will one day crack and California will slide into the sea. The San Andreas Fault is more accessible than any other fault in the world.

They are uncrowded and peaceful, perfect for family outings. There is abundant camping, bird watching, wild flowers and wildlife, rock collecting and natural beauty along the way.

Click on arrows and slide left and right to see labels. The San Andreas Fault is the transform plate boundary where a thin sliver of western California, as part of the Pacific Plate, slides north-northwestward past the rest of North America. In the Caribbean Sea, the U.

Virgin Islands lie along a transform plate boundary where the small Caribbean Plate moves eastward past the oceanic part of the North American Plate. Lillie, New York, W. Norton and Company, pp.

This feature includes the famous San Andreas Fault, responsible not only for destructive earthquakes, but also for the spectacular scenery of the San Francisco Bay area and other coastal regions of California. The San Andreas Fault is responsible for most of the movement in western California, causing a sliver of the state to slide past the rest of the continent.

In Mexico, a combinatiion of divergent and transform plate boundary motion is opening the Gulf of California, causing the Baja Peninsula to separate from the rest of Mexico. Letters in ovals are abbreviations for NPS sites listed above.

Marshak, , W. Cabrillo National Monument south of San Diego also lies within the broad zone of deformation between the two plates. The transform plate boundary between the Pacific and North American Plates in western California formed fairly recently. About million years ago, a large tectonic plate called the Farallon Plate started to subduct beneath the western edge of North America.

This resulted in a line of volcanoes stretching all the way from what is now Alaska to Central America. Beginning about 30 million years ago, so much of the Farallon Plate was consumed by subduction that the Pacific and North American plates were in contact, forming the San Andreas transform plate boundary in western California.

Over time, the San Andreas transform plate boundary has grown longer as the Farallon Plate split into two separate plates—the Juan de Fuca Plate on the north, and the Cocos Plate on the south. Remnants of the ancient volcanic mountain chain remain. In central and southern California, for example, the volcanoes have largely eroded away and massive areas of granite from the cooled magma chambers form portions of the Sierra Nevada Mountains, including Yosemite National Park.

Forty million years ago, a large tectonic plate, known as the Farallon Plate, was between the Pacific and North American plates. A transform plate boundary developed where the Pacific Plate was in contact with the North American Plate and the volcanism ceased in central California. Farther east, the continent began to rift apart in the Basin and Range Province.

The Sierra Nevada are the eroded remnants of the volcanic arc developed when the Farallon Plate subducted beneath the continent. The San Andreas Fault is just one of several faults that accommodate the transform motion between the Pacific and North American plates.

The plate boundary is a broad zone of deformation with a width of about 60 miles kilometers. Along much of the boundary, the bulk of the motion occurs along the San Andreas Fault.

Other parks in the region, namely Pinnacles, Channel Islands and Joshua Tree national parks, Cabrillo National Monument and Santa Monica Mountains National Recreation Area, reveal evidence of the shearing, rotation, and uplift that occurs within the broad zone of deformation between the two plates. Deformation along the transform plate boundary in California can be visualized by placing a deck of cards between your hands in a praying position.

Imagine that your left hand is the undeformed Pacific Plate, your right hand the intact North American Plate. Notice what happens as you move your left hand away and slide your right hand toward you. The cards slip along their faces, forming a broad zone of shearing between your unaffected hands. For western California, each slipping card face would be a fault surface. The broad zone of transform motion between the Pacific and North American plates formed numerous slivers of mountain ranges with narrow valleys in between.

The valleys are commonly due to erosion along individual fault lines. Lillie, Wells Creek Publishers, 92 pp. The broad zone of shearing at a transform plate boundary includes masses of rock displaced tens to hundreds of miles, shallow earthquakes, and a landscape consisting of long ridges separated by narrow valleys.

The San Andreas Fault is just one of many active earthquake faults in a broad zone of shearing along the transform plate boundary in the San Francisco Bay Area. These forces also create a sheared-up landscape that includes spectacularly beautiful coastlines and economically important harbors. Thousands of earthquakes over millions of years have built this landscape not only along the major fault line—the San Andreas Fault—but also on other faults within the broad zone of shearing between the Pacific and North American plates.

For example, rocks found today in Point Reyes National Seashore north of San Francisco were originally part of the line of granite rocks formed beneath ancient subduction zone volcanoes. The plate motion has plucked the rocks from their original position and moved them more than miles north-northwestward to their current position at Point Reyes.

Other rocks in the San Francisco Bay Area were originally part of an accretionary wedge, similar to rocks found today in the coastal ranges of the Cascadia Subduction Zone in northern California, Oregon, and Washington.