Extensional margins

Intercontinental rift zones

Spreading centers

Spreading Centers

Iceland Oceanic ridges

Gulf of Suez Rift

Intercontinental rifting

Basin and Range

Extensional faults in Canyonlands National Park, Utah

Analog models of extension

Go to movie of our sandbox experiment

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Analog models of extension

Claybox experiments at UMass

Investigations with extension

experiment in progress at UMass with undergraduates

Aims of the investigation:

Does the Earth’s crust deform under extension the same as under contraction?

Is the pattern of earthquakes the same in extension and contraction?

Wasatch Mountains in Utah

Questions of investigation:

How does topography change during extension?

What causes the topography to change?Where are the active

faults located?How many faults are

active at any time?

Activities

ObserveSketch <-> observeLabelMeasureGraphPredict

Data Collection

# turns (cm) Basin depth (cm)

Basin length (cm)

# active faults

Extensional faults dip different from contraction

Shallow faults form during contraction (30˚ dip)Steep faults form during extension (60˚ dip)It is consistent!

Extension and contraction are 90˚ apart

6030

3060

Effect of Existing faults

Cut a fault into the sand pack that might not be oriented as favorably for slip as a new fault.Does the new fault form or

old fault reactivate?

Hey what about strike slip?

Clay shows interesting patterns of echelon cracksClay cake on top of two

boardsPull one board slowly

From SERC