Tectonic FeaturesILAN ALYSSA RYAN

Tectonic Features•Cuesta•Hogback•Fault Scarp •Shutter Ridge•Sag Pond•Offset Stream Channel•Horst•Graben

Fault Scarp•At the beginning of earthquakes, fault slip starts miles below the earth's surface and then extends outward and upward. Most earthquakes (small to moderate earthquakes, in particular) stop before the fault slip reaches the ground surface, but during large earthquakes the fault slip usually creates a break (or fault scarp) at the ground surface.

Fault Scarp: What to look for•Fault scarps appear as a step in the ground, and can be a few inches to several tens of feet high, but they are extremely difficult to recognize unless they are at least a few feet high.

•With time, the scarp face becomes worn down by erosion and covered by vegetation, making the scarp much less obvious.

Fault Scarp Satellite Images

Fault Scarp Pictures

Fault Scarp Topographic Map

Sources for Fault Scarp:

•http://earthquake.usgs.gov/regional/imw/imw_rito_seco/

•http://www.nbmg.unr.edu/dox/nl/nl14a.htm

Shutter Ridge

•“A shutter ridge is a ridge… along a fault line, blocking or diverting drainage. Typically, a shutter ridge creates a valley corresponding to the alignment of the fault that produces it.” (Wikipedia)

Shutter Ridge Topographic Map

Shutter Ridge Satellite Images

Shutter Ridge Pictures

Sag Pond Topographic Map

Sag Pond

•“A sag pond is a small body of water occupying an enclosed depression or sag formed where active or recent fault movement has impounded drainage. (Sci- Tech Dictionary)

Sag Pond Satellite Image

Sag Pond Picture

Hogback•Homoclinal ridge (shown on next slide)•Composed of steeply tilted strata of

protruding rock•Resembles high, knobby spine between

the shoulders of a hog•Defining characteristic: steep dip slope

greater than 30°•Near symmetric slope on each ridge face.

A cuesta is a homoclinal ridge with a more gentle dip slope.

Hogback Diagram

Process of Formation•Two strata are different types of

sedimentary rock with differing weathering rates

•Softer rock erodes quicker than overlying hard rock

•Softer rock retreats to a point where hard and soft rock strata are adjacent

•Creates cliffs that steepen as the softer rock continues to erode.

http://academic.emporia.edu/aberjame/field/rocky_mt/hogback1.jpg

http://www.cliffshade.com/colorado/dakota_hogback/dak04.jpg

http://www.cliffshade.com/colorado/dakota_hogback/dak04.jpg

Cuesta

•Ridge formed by gently tilted sedimentary rock strata (layers)

•Homoclinal structure•Steep slopes•Rock layers exposed on edges

Cuesta on contour map:

“Cuesta del Burro, Texas”

Cuesta contour map

Offset Stream Channel:Stream offsets are the counterpart to shutter ridges, a sign of lateral movement on strike-slip faults like the San Andreas fault.

Earlier earthquakes clearly helped produce the stream offset, on the San Andreas Fault in Carrizo Plain National Monument.

Offset Stream Channel

HorstA horst is found together with a graben. The graben are the down-dropped blocks and the horst are the unthrown blocks that lie next to the graben.

Flash animation: http://earthquake.usgs.gov/learn/animations/animation.php?flash_title=Horst+and+Graben+Flash+Animation&flash_file=horstandgraben&flash_width=380&flash_height=210

Graben

A graben is a down-dropped block of the earth’s crust resulting from extension, or pulling, of the crust.

Death Valley, California

Death Valley, California

Sources•http://www.thulescientific.com/

MustangRidgeSagPond.jpg•http://edcsns17.cr.usgs.gov/

EarthExplorer/?dataset_name=MAPS_LARGE

•http://www.trails.com/topo.aspx?lat=46.78139&lon=-69.05556&s=50&name=Sag+Pond

•http://blueschist.org/PhotosShutterRidge.aspx