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, or at some angle to the surface of the earth.  The slip direction can also be at any angle.

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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 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...
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Date published: March 27, 2014

Prior Great Earthquakes Unveiled at the Western Edge of the 1964 Alaska Rupture

Ever since the great magnitude 9.2 earthquake shook Alaska 50 years ago today, scientists have suspected that the quake's rupture halted at the southwestern tip of Kodiak Island due to a natural barrier.

Attribution: Natural Hazards
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.

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May 25, 2017

PubTalk 5/2017 — Underwater secrets of the Hayward fault zone

Title: Underwater Secrets of the Hayward Fault Zone: Integrated 3D imaging to understand earthquake hazards 

  • Underwater imaging provides a unique opportunity to study urban fault hazards.
  • How do we link surface structures to depths where earthquakes occur?
  • How does "acoustic trenching" help us understand earthquake history?
February 24, 2014

PubTalk 2/2014 — 1964 Great Alaska Earthquake and Tsunami 50th Anniv.

By George Plafker, USGS Geologist Emeritus

 

  • March 27th, 1964, one of the most violent earthquakes of all time rocked southern Alaska.
  • More than 50,000 square miles of the state was tilted to new elevation, and the resulting property damage disrupted the state's economy.
  • Within 24 hours, a team of USGS geologists
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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

Image shows a road split due to earthquake damage
November 30, 2000

1964 Alaskan Earthquake Damage

Damage from the 1964 Alaskan Earthquake. Credit: USGS

Image: Aerial Photo of the Surface Rupture
October 1, 1999

Aerial Photo of the Surface Rupture

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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).

Image: Surface Rupture in Northwest Saudi Arabia

Surface Rupture in Northwest Saudi Arabia

Wendy McCausland of the USGS Volcano Disaster Assistance Program and Hani Zahran of the Saudi Geological Survey view the southern end of the surface fault rupture caused by a M5.4 earthquake in the Saudi Arabian desert on May 19, 2009. The ground displacements in the soft sediments of the foreground are greater than in basement rocks of the background because sediments

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