Introduction to Faults (p. 269-279; 286-296)

1) Hanging wall vs. footwall 2) Fault names: based on geometry & kinematics 3) Characteristics and terminology

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Strike-slip faults Normal faults

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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 (sinistral) right lateral (dextral) left lateral vs. right lateral: sense-of-slip relative to a chosen block

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) Cambrian limestone FW HW Tertiary conglomerate

Normal faults generally place younger and/or lower-grade rocks (in HW) on top of older and/or higher-grade rocks (in FW) young “dirt” HW FW high-grade gneiss

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 blueschist sandstone FW

Normal faults accommodate lengthening

Thrust faults accommodate shortening

http://earth.leeds.ac.uk/learnstructure/index.htm

Slip vs. Separation Slip: actual relative displacement Separation: 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