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Introduction to Faults(p. 269-279; 286-296)
1) Hanging wall vs. footwall
2) Fault names: based on geometry & kinematics
3) Characteristics and terminology- Strike-slip faults
- Normal faults- Thrust faults
Fault: Fractures along which there is visible offset by shear displacement; generally planar or curviplanar
Strike-slip faults: Accommodate horizontal slip between adjacent blocks
left lateral vs. right lateral: sense-of-slip relative to a chosen block
left lateral (sinistral)
right lateral (dextral)
What is it? left lateral vs. right lateral
Las Vegas shear zone
What is it?
What is it? (interpretation)left-lateral strike-slip fault
Hanging wall: The block toward which the fault dips.
Footwall: The block on the underside of the fault.
Normal fault: hanging wall moves down with respect to footwall
Normal faults generally place younger and/or lower-grade rocks (in HW) on top of older and/or higher-grade rocks (in FW)
Tertiary conglomerate
Cambrian limestone
HWFW
high-grade gneiss
young “dirt”
FW
HW
Normal faults generally place younger and/or lower-grade rocks (in HW) on top of older and/or higher-grade rocks (in FW)
Thrust fault (reverse fault): hanging wall moves upward relative to footwall
HW
FW
Thrust faults generally place older and/or higher-grade rocks (in HW) on top of younger and/or lower-grade rocks (in FW)
Thrust faults generally place older and/or higher-grade rocks (in HW) on top of younger and/or lower-grade rocks (in FW)
Thrust faults generally place older and/or higher-grade rocks (in HW) on top of younger and/or lower-grade rocks (in FW)
HW
FWblueschist
sandstone
Normal faults accommodate lengthening
Thrust faults accommodate shortening
http://earth.leeds.ac.uk/learnstructure/index.htm
Slip vs. Separation
Slip: actual relative displacementSeparation: apparent relative displacement
A real example of apparent separation vs. true slip!
The key to describing slip along a fault lies in measuring
(1) Direction of displacement
(2) Sense of displacement
(3) Magnitude of displacement
Listric: curved faults that flatten with depth
Fault scarp: results when a fault displaces the ground surface
Map Symbols: a start
- Strike-slip fault- Normal fault- Thrust fault- Fault dip and slip vector
Next lecture: Intro to folds
Read pp. 372-413
Important terminology/concepts
Faults- how are they defined?
Hanging wall
Footwall
Strike-slip fault; left-lateral (sinistral) vs. right-lateral (dextral)
Normal faults: younger/lower grade on older/higher grade
Lengthening
Thrust faults: older/higher grade on younger/lower grade
Shortening
Slip vs. Separation?
Drag fold
Listric
Fault scarp