Copyright Information: All images are in the public domain and available for free. If you use this image, credit NOAA/NGDC, National Geophysical Data Center. |
This fault scarp near Hebgen Lake, Montana, after the magnitude 7.1 earthquake of August 18, 1959, shows a dip-slip movement of 5.5 to 6.0 m. Since the earth above the fracture moved down in respect to the earth below the fracture, the fault is known as a normal fault. Such faults result from extension or stretching of the rock layers. Maximum vertical displacement was 6.4 m observed near Red Canyon Creek. Considerable cracking and shifting of roadways, and the destruction of much timber, caused damage exceeding $11 million. In Yellowstone National Park new geysers started erupting, and large steaming cracks, resulting from massive slumping, were observed after the quake. Image Credit: National Geophysical Data Center Through the study of faults and their effects, much can be learned about the size and recurrence intervals of earthquakes. Faults also teach us about crustal movements that have produced mountains and changed continents. Initially a section of Earth's crust may merely bend under pressure to a new position. Or slow movement known as seismic creep may continue unhindered along a fault plane. However stresses often continue to build until they exceed the strength of the rock in that section of crust. The rock then breaks, and an earthquake occurs, sometimes releasing massive amounts of energy. The ensuing earth displacement is known as a fault. This slide set describes the mechanism and types of faulting. It illustrates a variety of fault expressions in natural and manmade features. |
|
