Produced by
M. Mustoe Ph.D. Geographer Eastern Oregon University
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The Four BASIC Types Of Faults
(This does not include growth faults)


The Normal Fault

The normal fault is not necessarily normal in the sense that it is common....because.... it is not the most common of faults. However what is normal about them is that their movement tends to follow the gravitational pull on the fault blocks involved. The fault plane on the normal fault is generally very steep. In a normal fault the two involved blocks are (by gravity) pulling away from one another causing one of the fault blocks to slip upward and the other downward with respect to the fault plane (it is hard to determine whether both or just one block has moved.). The exposed upward block forms a cliff-like feature known as a fault scarp. A scarp may range from a few to hundreds of meters in height and their length may continue for 300 or more kilometers (around 200 miles).


The Reverse Fault

The reverse fault is a normal fault except the general movement of the fault blocks is toward
each other, not away from each other as in the normal fault. This forms a thrust fault type expression on the surface with material overlaying other material.

 

 USGS Photo

The night of 17 August marks the aniversary of a little talked about yet profoundly significant earthquake known as the Hebgen Lake, or Montana-Yellowstone Eartquake. The event took place in 1959 in a remote...but well visited region around West Yellowstone, Montana. On that night nearly 18,000 campers and park personnel, felt a shock that had originated ten miles below the suface in the vicinity of the Madison River Canyon. As a result of that intensity 7.1 earthquake, 43 million cubic yards of rock slid as a block into the Madison Canyon daming up the Madison River, below Hebgen Dam. The lake basin behind Hebgen dam tilted with the south side rising and the north side dropping. This caused a seische...a lake tsunami...that crested the dam four times and kept the lake in motion for nearly 11 hours. At Yellowstone Park, hot springs and geysers, that had never been known to erupt before erupted. The shock wave was felt in an area of 500,000 sqaure miles. It caused wells to fluxuate in Texas and and as far away as Hawaii and Puerto Rico. Nine people lost their lives and 19 were listed as missing in this event. The image above shows a fault scarp where the block was thrown down at one end of the valley. Displacement here was about 20 feet and ran hundreds of feet long.
New fault scarps along Hebgen Lake, Montana. About 20 feet displacement. This area covered the main road. U.S.F.S. Photo

The Initial Stages Of Landforms

The phrase "initial stage" means the beginning stages of a landform. Click here for a look at a graben and horst system.


Two More Fault Types

Transcurrent Fault (Strike-Slip Fault)

Probably the most well known and well studied fault is the transcurrent (strike-slip) fault known as the San Andreas fault of California. This fault marks the margin line between the Pacific and North American Plates. Movement on a strike strip fault is generally horizontal. On the surface, scarps form as hills crossing the fault zone are torn apart by movement over time. Actually anything crossing this fault zone is either slowly torn apart, or offset. Rivers crossing the fault line are called offset streams and are classic signatures of fault activity along the San Andreas. These faults can be very long, the San Andreas is nearly 600 miles long.


Thrust Fault

In the 1994 Northridge, California event, a deep thrust fault located about 18 km under the city of Los Angeles produced an eartquake that registered a magnitude of 6.7. When thrust faults are exposed on the surface overburnden material lies over the main block. They are normally associated with areas of folded surfaces and or mountaineous regions. The dip angles of thrust faults are normally not as steep as a normal fault. Chief Mountain, in Montana (one of the places we look at using the USGS quads in the principles of geography class) is an example of a thrust mountain.


e-mail the teacher click the seismogram

Just For Fun: The "grapevine hill" which disects the San Andreas Fault on Interstate 5 in Southern California is mentioned in what popular song? Better yet...who did the original version......here's a hint:
"My daddy said, son your're gonna drive me to drinkin' if you don't stop driving that .................."


Of Interest To My Geography Students

Internet Links To Earthquake Data and Information

New Information on the 01/02/28 Event
Idaho Geologic Survey

Oklahoma Geological Survey
Seismo-Surfing the Internet

North Idaho Seismic Network

University of Utah Intermountain West Earthquakes

Lewis and Clark Zone

Various Northwest Sites Boise State

NE of Olympia (Nisqually Earthquake) , 01/02/28 18:54:31 UTC 47.17N 122.73W Depth: 49.0 km 6.8M

Pacific Northwest Earthquakes USGS

1949 Seattle, 04 13 19:55:42 UTC, 6.9, MM VIII

1965, Puget Sound 04/29/1965 04 29 15:28:43.7 UTC, 6.5, VIII
(Felt all the way to B.C. and Montana, Dr M was in grade 5 during this one and still remembers it shaking the room)

University of Washington Geophysics

Pacific Northwest Earthquake Information (PN Seismograph Network)

Earthquakes for Kids and Grownups! USGS

Earthquake Hazards Program

The Southern California Earthquake Center

Earthquake information from the USGS

Recent Earthquake Data on the Net

Alaska earthquake Center

The Great Alaska Earthquake of 1964 (Attn. Kodiak Quiverings Assignment students)

UC Berkley Seismographic Station Home Page

About the Northridge Earthquake

Geologic Hazards Team

Earthquake Eyewitness Accounts (CNN)

Chronological Earthquake Index

Air Talk: Earthquakes and Structral Design

Northridge Earthquake Animations

Emergency Service Action

Northridge Slideshow Page

The Global Earthquake Response Center

UCD Active Tectonics

Responses to Radio Stations During the Loma Prieta Event

Collapse of Freeway in the Loma Prieta Event

Loma Prieta Earthquake

San Andreas Fault

Earthquake Warning System

Make Your Own Seismogram

Mono Lake Activity