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 displacements over geologic time.  During an earthquake, the rock on one side of the fault suddenly slips with respect to the other.  The fault surface can be horizontal or vertical or some arbitrary angle in between.

Earth scientists use the angle of the fault with respect to the surface (known as the dip) and the direction of slip along the fault to classify faults.  Faults which move along the direction of the dip plane are dip-slip faults and described as either normal or reverse (thrust), depending on their motion.  Faults which move horizontally are known as strike-slip faults and are classified as either right-lateral or left-lateral.  Faults which show both dip-slip and strike-slip motion are known as oblique-slip faults.

The following definitions are adapted from The Earth by Press and Siever.

normal fault - a dip-slip fault in which the block above the fault has moved downward relative to the block below.  This type of faulting occurs in response to extension and is often observed in the Western United States Basin and Range Province and along oceanic ridge systems.

Normal Fault Animation

thrust fault - a dip-slip fault in which the upper block, above the fault plane, moves up and over the lower block.  This type of faulting is common in areas of compression, such as regions where one plate is being subducted under another as in Japan.  When the dip angle is shallow, a reverse fault is often described as a thrust fault.

Thrust Fault Animation

Blind Thrust Fault Animation

strike-slip fault - a fault on which the two blocks slide past one another.  The San Andreas Fault is an example of a right lateral fault.

Strike-slip Fault Animation

A left-lateral strike-slip fault is one on which the displacement of the far block is to the left when viewed from either side.

A right-lateral strike-slip fault is one on which the displacement of the far block is to the right when viewed from either side.

Related Content

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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 three-dimensional fault intersects...

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...

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...

What is a "Quaternary" fault?

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

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

An online map of U.S. Quaternary Faults (faults that have been active in the last 1.6 million years) 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...

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 research this yourself in journals, books, or online. A good general reference book is USGS Professional Paper 1527 (published 1993): Seismicity of the United States, 1568-1989 (Revised) . Earthquakes that occurred prior to 1990 should be described in the Professional Paper along with other historical earthquakes in the vicinity...

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 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: 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.

Date published: December 4, 2003

Cat Scan'-Like Seismic Study of Earthquake Zone Helps Set Stage for Fault Drilling Project

In a first of its kind study U.S. Geological Survey (USGS) and Duke University seismologists have used tiny "microearthquakes" along a section of California’s notorious San Andreas Fault to create unique images of the contorted geology scientists will face as they continue drilling deeper into the fault zone to construct a major earthquake "observatory.

Date published: November 7, 2002

Alaska Interior Reveals Scars and Ruptures from 7.9 Denali Fault Quake

Sunday’s magnitude 7.9 earthquake in central Alaska created a scar across the landscape for more than 145 miles, according to surveys conducted the past two days by geologists from the U.S. Geological Survey and the Alaska Division of Geological and Geophysical Survey.

Filter Total Items: 6
Rufus Catchings points out a surface fault
February 12, 2018

Rufus Catchings points out a surface fault

Rufus Catchings points out a surface fault in southern California (2011). Splay of San Andreas Fault.

Fault offset along the Queen Charlotte Fault
November 24, 2016

Queen Charlotte Fault

Seabed expression of the Queen Charlotte Fault in southeastern Alaska.

Exposed faults
September 10, 2011

Exposed faults

Two faults (located on either side of project geologist Chris Fridrich) cutting Pleistocene fluvial gravels on the northern edge of the Poncha mountain block. These and other young faults exposed in area help reveal the latest kinematic (movement) and paleostress histories of the mountain block.

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

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).

block diagram illustrating strike-slip fault

Block diagram of a Strike-Slip fault.

Block diagram of a Strike-Slip fault.