Introduction to Faults (p. 269-279; 286-296) 1) Hanging wall vs. footwall 2) Fault names: based on...

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