Faults and FoldsPart 1

Diastrophism Processes

Breaking & Warping Earth

• Extension - Normal faulting (part 1)

• Compression - Thrust faulting (part 1)• Transform – Strike-slip faulting (part 2)• Folding from Compression (part 2)

Faults and FoldsPart 1

What is a fault?

What is an earthquake?

Online Animations

Earthquake Visualizations

http://serc.carleton.edu/NAGTWorkshops/visualization/collections/earthquakes.html

Fault – rocks snapped

Earthquakes occur along active faults where energy is stored and suddenly released when the stresses along the fault exceed the frictional forces resisting motion. The longer the time interval (seismic gap) between seismic events the greater the magnitude of the earthquake.

Earthquakes are the most destructive natural forces on Earth. The Alaskan earthquake of 1964 was one of the ten most powerful seismic events in the past century. The image was taken in down town Anchorage.

Structural damage from fire can be greater than that produced from direct ground-shaking. The images above are from Kobe, Japan where a 7.0 earthquake struck in 1995. Over $100 billion damage was sustained from structure collapse and fire.

Hanshin Expressway Kobe Japan

Faults and Folds

1. Extension - Normal faulting

2. Compression - Thrust faulting

3. Transform – Strike-slip faulting

4. Folding from Compression

Compression, Tension, and Shearing Stress

Strike-slip

Thrust faulting

Normal

Folding &

1. Extension - Normal faulting

Classroom Resource

Fault Scarp (escarpment)from single event

From Multiple Events

Wasatch Faulting over Millions of Years: See Classroom Resource Folder

Over several million years

Sierra Nevada

Normal Fault Scarp Forms

Triangular Facets – produced by erosion of the fault scarp by

river valleys

Alternating normal faults lead to a characteristic pattern called aHorst and Graben system. An area under tension will often haveMultiple mountain ranges as a result.

Classroom Resource

Block Faulting in the Basin and Range

Why is Basin & Range Extending?

Classroom Resource

San Andreas

formation

stopped

compression

and started

extension

Extension produce deep valleys filled with gravels (and water)

So much extension that the crust popped back up

Isostacydemands

that if crustthins, the root

rises up …

so Camelback is just a flake off the bulge

White TankMetamorphic

CoreComplex

2. compression

thrust faulting

REVERSE FAULTS: Hanging wall moves up relative to footwallResult of compression: plates collidingTwo types: low-angle or thrust faults, and high-angle reverse faults

Individual layers can move 100’s of kilometersAlps are a great example

Classroom Resources

Convergent Plate Boundaries and Thrust Faulting

Ocean-Oceancollision forms Island Arc: Japan,Aleutians, Cent. Am.

Continent-Continentcollision formsFolded Mountain Belt:Alps, Himalayans, Appalachians

Thrust Faulting & Mountains

Dezes, U. of Lausanne

Edwards & Kidd, U. of Albany

Lewis Thrust Fault

1971 Ms 6.6 SAN FERNANDO

EARTHQUAKE

•1.4 m slip on 20x14 km2 fault

•Thrust faulting from compression across Los Angeles Basin

•Fault had not been previously recognized

•65 deaths, in part due to structural failure

•Prompted improvements in building code & hazard mapping

$20B damage makes it the most costly earthquake to date in the U.S.

S&W 4.5-9

Los Angeles Basin

Thrust earthquakes indicate shortening

1994 Northridge Ms 6.7

Geologist are now aware that there can be major subduction zone earthquakes along our coastline that are capable of generating magnitude 8-9 seismic events. Offset along the Cascadia subduction zone can cause major coastal subsidence and tsunami events along with the expected ground shaking.

Downtown Seattle following the 1949 earthquake.

As the floor of the Puget Sound was vertically offset, a tsunami was generated that inundated seveal of the south-facing embayments on Whidbey Island. A sand sheet (light gray near the top of the section) is preserved in Cultus Bay sediment record. Radiocarbon dating indicates that deposition of the sand sheet is coincident with uplift of the Seattle Fault 1100 years ago.

Cultus Bay

Sandy HookScatchet Head

During the 1700 AD event a large tsunami was generated that deposited a sand sheet over the topsoil and buried a Native American hearth site.

The tidal mud was deposited over the sand sheet following coastal subsidence during the subsequent centuries.

Taiwan Thrust Faulting ‘99

Campania Italy Thrust Faulting ‘80

Imagery seen in this presentation is courtesy of Ron Dorn and other ASU colleagues, students and colleagues in other academic departments, individual illustrations in scholarly journals such as Science and Nature, scholarly societies such as the Association of American Geographers, city,state governments, other countries government websites and U.S. government agencies such as NASA, USGS, NRCS, Library of Congress, U.S. Fish and Wildlife Service USAID and NOAA.cs