Why are there so many earthquakes and faults in the Western United States?

This region of the United States has been tectonically active since the supercontinent Pangea broke up roughly 200 million years ago, and in large part because it is close to the western boundary of the North American plate.  Since the formation of the San Andreas Fault system 25-30 million years ago, the juxtaposition of the Pacific and North American plates has formed many faults in California that accommodate lateral motion between the plates.  North and east of California, the Basin and Range province between the Wasatch Mountains in Utah and the Sierra Nevada Mountains in eastern California is actively spreading and stretching westward.

In New Mexico and west Texas, similar spreading has opened a north-south rift that starts in central Colorado and extends into northern Mexico. The geologic conditions and plate tectonic setting in much of the Western U.S. has resulted in the region being underlain by relatively thin crust and having high heat flow, both of which can favor relatively high deformation rates and active faulting.

In contrast, in the Central and Eastern U.S. (CEUS) the crust is thicker, colder, older, and more stable. Furthermore, the CEUS is thousands of miles from active plate boundaries, so the rates of deformation are low in this region. Nevertheless, the CEUS has had some rather large earthquakes in historical times, including a series of major earthquakes near New Madrid, Missouri in 1811-1812, a large earthquake near Charleston, S.C. in 1886, and the Cape Ann earthquake northeast of Boston in 1755.

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Where are the fault lines in the Eastern United States (east of the Rocky Mountains)?

Faults are different from fault lines. A fault is a three-dimensional surface within the planet Earth. At the fault, rocks have broken. The rocks on one side of the fault have moved past the rocks on the other side. In contrast, a fault line is a line that stretches along the ground. The fault line is where the fault cuts the Earth's surface...

Why are there so many faults in the Quaternary Faults Database with the same name?

Many faults are mapped as individual segments across an area. These fault segments are given a different value for name, number, code, or dip direction and so in the database each segment occurs as its own unique entity. For example, the San Andreas Fault has several fault segments, from letters a to h, and fault segment 1h has segments with age...

Why are there no faults in the Great Valley of central California?

The Great Valley is a basin, initially forming some ~100 million years ago as a low area between the subducting ocean plate on the west (diving down under the North American plate) and the volcanoes to the east (now the Sierra Nevada mountains). Since its formation, the Great Valley has continued to be low in elevation. Starting about 15 million...

What is a "Quaternary" fault?

A Quaternary fault is one that has been recognized at the surface and which has moved in the past 1,600,000 years, a portion of the Quaternary epoch.

Where can I find a fault map of the US? Is one available in GIS format?

An online map of US Quaternary Faults is available via the Quaternary Fault and Fold Database . There is an interactive map application to view the faults online and a seperate database search function. KML (Google Earth-type) files and GIS shape files are also available for download from the site. The interactive map provides detailed reports for...

I am looking to buy land near the location of a large historical earthquake.  I am wondering where the fault line runs.  What is the seismic activity in the area today?  How did the quake change the contours and elevations of the area?

You will have to do some research on this yourself, either in journals or books or at another web site. A good first book reference in general for this sort of information is Stover and Coffman, (1993) Seismicity of the United States, 1568-1989 (Revised), U.S. Geological Survey professional Paper 1527. (This reference ought to be at a large...

How do I find fault or hazard maps for California?

An online map of faults that includes California can be found in the Faults section of the Earthquake Hazards Program website. Choose the Interactive Fault Map, or download KML files and GIS shapefiles from the links on the page. USGS seismic hazard maps, data and tools for California and other parts of the United States can be found in the...

What is a fault and what are the different types?

A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep . Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated...

What is the relationship between faults and earthquakes?  What happens to a fault when an earthquake occurs?

Earthquakes occur on faults - strike-slip earthquakes occur on strike-slip faults, normal earthquakes occur on normal faults , and thrust earthquakes occur on thrust or reverse faults. When an earthquake occurs on one of these faults, the rock on one side of the fault slips with respect to the other. The fault surface can be vertical, horizontal,...
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Date published: April 24, 2018

East vs West Coast Earthquakes

Why was an earthquake in Virginia felt at more than twice the distance than a similar-sized earthquake in California? The answer is one that many people may not realize. Earthquakes east of the Rocky Mountains can cause noticeable ground shaking at much farther distances than comparably-sized earthquakes in the West.

Date published: June 26, 2014

New Audiences, New Products for the National Seismic Hazard Maps

New Audiences, New Products for the National Seismic Hazard Maps

Date published: February 24, 2014

The 1964 Great Alaska Earthquake and Tsunami


On March 27th, 1964, the second largest instrumentally recorded earthquake worldwide rocked southern Alaska for 4 to 5 minutes. In addition to the earthquake, the event triggered a major tsunami that caused casualties and damage from the Kodiak Islands to northern California.

Date published: March 9, 2006

A Virtual Tour of the Hayward Fault

The U.S. Geological Survey has a new website that offers a virtual tour of the Hayward fault.

Filter Total Items: 7
Image: Denali Fault: Gillette Pass
November 12, 2002

Denali Fault: Gillette Pass

View northward of mountain near Gillette Pass showing sackung features. Here the mountaintop moved downward like a keystone, producing an uphill-facing scarp. The main Denali fault trace is on the far side of the mountain and a small splay fault is out of view below the photo.

Image: Denali Fault
November 4, 2002

Denali Fault

At pass west of Delta River. Here there was roughly 5 m of offset. Note the push up in the background. There is permafrost at the bottom of the cracks.

Image shows an aerial view of the San Andreas Fault
November 30, 2000

San-Andreas Fault

Aerial photo of the San Andreas Fault in the Carrizo Plain. By Ikluft - Own work, GFDL, https://commons.wikimedia.org/w/index.php?curid=3106006

Map of known active geologic faults in the San Francisco Bay region

Map of known active geologic faults in the San Francisco Bay region

Map of known active geologic faults in the San Francisco Bay region, California, including the Hayward Fault.  The 72 percent probability of a magnitude (M) 6.7 or greater earthquake in the region includes well-known major plate-boundary faults, lesser-known faults, and unknown faults.  The percentage shown within each colored circle is the probability that a M 6.7 or

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Interactive Quarternary Fault Database

Interactive Quarternary Fault Database

This database contains information on faults and associated folds in the United States that demonstrate geological evidence of coseismic surface deformation in large earthquakes during the Quaternary (the past 1.6 million years).

 location of and evidence for recent movement on active fault traces within the Hayward Fault Zone, California

Traces of the Hayward Fault, California

The purpose of this map is to show the location of and evidence for recent movement on active fault traces within the Hayward Fault Zone, California.  The mapped traces represent the integration of the following three different types of data: (1) geomorphic expression, (2) creep (aseismic fault slip),and (3) trench exposures. 

Attribution: Natural Hazards