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
