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Strike

Strike and Dip


UseEdit

Strike and dip are used to describe the orientation of a rock bed, fault, fracture, cuestas, igneous dikes, and sills.

DefinitionEdit

Strike is defined as the direction of the line formed by the intersection of a fault, bed or other planar feature and a horizontal plane. Dip is the angle at which a planar feature is inclined to the horizontal plane; it is measured in a vertical plane perpendicular to the strike of the feature.

New brunton

A Brunton Compass

A bed will be used in this description. For a recently created flat bed it would have a dip of 0° and a directionless strike. When it is tilted it gains a direction. The bed is usually not homogeneous since it usually folds when tilting, fractured, or compressed. A strike of 000° means the bed is dipping east; 090° for south; 180° for west; and 270° for north. A drip of 0° means its flat and 90° for a vertical bed.

Trend is the direction of the line formed by the intersection of the planar feature with the ground surface; trend is the same as strike only if the ground surface is parallel to the horizontal plane. Plunge is the vertical angle between the horizontal plane and the axis or line of maximum elongation of a feature.


How ToEdit

The first thing that needs to be done is to calibrate your compass to the magnetic declination. Magnetic declination is the difference between geographic north and magnetic north, with respect to your position. To determine what degree you need to set your compass to consult the picture below.

Isogonic

Isogonic Chart

Focalmechs

Focal Mechanism Diagram



To find the strike, stand so that the dip of the bed slopes to the right (this is known as the Right Hand Rule). Orient the long arm of the Brunton in the direction you are facing, and place the side of the Brunton against the rock. Level it so that the bubble in the flat level is in the center of its circle, then read the number that the north end of the needle is pointing at. That number is your strike.

To find the dip, orient your Brunton perpendicular to the strike. The easiest way to do this is to let water fall on the surface of the rock and it tends to roll down the steepest angle. Place the Brunton against the rock, on the side this time, with the long arm pointed down the dip of the bed.

It may be complicated sometimes if a rock surface is rough. To deal with this you put a flat object, like a clipboard, on the rock to determine its strike and dip. Due note that if the surface is weathered too much then it may not be the true dip of that part of the bed; so you would need to search other places along the bed to find a reasonable outcrop.

Record the data of a bed with a stroke of 15 and dip of 45 as 015/45.

This can be very useful when figuring out if the area is influenced by a thrust fault, normal fault, or strike slip fault through the use of a focal mechanism diagram.


ReferencesEdit

http://facweb.bhc.edu/academics/science/harwoodr/geol101/study/structur.htm

http://homepage.usask.ca/~mjr347/prog/geoe118/geoe118.045.html

http://www4.uwm.edu/course/geosci697/sections/sections.html

http://www.nrsweb.com/shop/product.asp?pfid=7442

http://en.wikipedia.org/wiki/Strike_and_dip

http://www.nlb-creations.com/sites/summary1/basics/brunton.html

http://www.britannica.com/EBchecked/topic/569093/strike

http://en.wikipedia.org/wiki/Focal_mechanism

http://all-geo.org/highlyallochthonous/2009/12/5-focal-mechanisms/

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