faults

fractures

A rock under enough stress will fracture. There may or may not be movement along the fracture.

dipslip faults

There are two types of dip-slip faults. In a normal fault, the hanging wall drops down relative to the footwall. In a reverse fault, the footwall drops down relative to the hanging wall. This diagram illustrates the two types of dip-slip faults: normal faults and reverse faults. Imagine miners extracting a re- source along a fault. The hanging wall is where miners would have hung their lanterns. The footwall is where they would have walked. A thrust fault is a type of reverse fault in which the fault plane angle is nearly horizontal. Rocks can slip many miles along thrust faults (Figure 1.4). At Chief Mountain in Montana, the upper rocks at the Lewis Overthrust are more than 1 billion years older than the lower rocks. How could this happen? Normal faults can be huge. They are responsible for uplifting mountain ranges in regions experiencing tensional stress.

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joints

If there is no movement on either side of a fracture, the fracture is called a joint. The rocks below show horizontal and vertical jointing. These joints formed when the confining stress was removed from the rocks as shown in (Figure

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faults

If the blocks of rock on one or both sides of a fracture move, the fracture is called a fault (Figure 1.2). Stresses along faults cause rocks to break and move suddenly. The energy released is an earthquake. How do you know theres a fault in this rock? Try to line up the same type of rock on either side of the lines that cut across them. One side moved relative to the other side, so you know the lines are a fault. Slip is the distance rocks move along a fault. Slip can be up or down the fault plane. Slip is relative, because there is usually no way to know whether both sides moved or only one. Faults lie at an angle to the horizontal surface of the Earth. That angle is called the faults dip. The dip defines which of two basic types a fault is. If the faults dip is inclined relative to the horizontal, the fault is a dip-slip fault (Figure 1.3).

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strikeslip faults

A strike-slip fault is a dip-slip fault in which the dip of the fault plane is vertical. Strike-slip faults result from shear stresses. Imagine placing one foot on either side of a strike-slip fault. One block moves toward you. If that block moves toward your right foot, the fault is a right-lateral strike-slip fault; if that block moves toward your left foot, the fault is a left-lateral strike-slip fault (Figure 1.5). Californias San Andreas Fault is the worlds most famous strike-slip fault. It is a right-lateral strike slip fault (See opening image). People sometimes say that California will fall into the ocean someday, which is not true. Strike-slip faults. Click image to the left or use the URL below. URL:

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instructional diagrams

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questions

if a miner is standing on a fault, the _ wall is where his safety helmet would be and the _ wall is where his steel toed boots would be.

a) tail; head

b) head; tail

c) foot; hanging

-->  d) hanging; foot

if there is no movement on either side of a fracture, the fracture is called this.

-->  a) a joint

b) a fault

c) a slip

d) a dip

mountain ranges can uplift on these types of faults.

a) strike-slip faults

b) reverse faults

-->  c) normal faults

d) tensional faults

if the angle of a fault is inclined relative to the horizontal it is a

a) joint

b) reverse fault

-->  c) dip-slip fault

d) strike-slip fault

horizontal-appearing layers can have a younger rock below an older rock if they are separated by a thrust fault.

-->  a) true

b) false

why wont california west of the san andreas fault fall into the pacific ocean?

-->  a) the motion along the fault is horizontal.

b) the motion along the fault is thrust.

c) that piece of land is being faulted upward, not downward.

d) there is too much friction.

strike slip faults result from ____ stresses.

a) compressive

b) diagonal

c) tensional

-->  d) shear

this type of reverse fault has a plane angle that is nearly horizontal.

a) normal fault

-->  b) thrust fault

c) strike-slip fault

d) dip-slip fault

at the san andreas fault, the pacific plate is moving north relative to the north american plate. this means that the san andreas is a

-->  a) right-lateral strike-slip fault.

b) left-lateral strike-slip fault.

c) dip slip fault.

d) thrust fault.

in a normal fault, the hanging wall goes up and the footwall goes down.

a) true

-->  b) false

diagram questions

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