faults and folds part 1 diastrophism processes breaking & warping earth
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Faults and FoldsPart 1Diastrophism 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 AnimationsEarthquake Visualizationshttp://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 FoldsExtension - Normal faulting Compression - Thrust faultingTransform Strike-slip faultingFolding from Compression
Compression, Tension, and Shearing StressStrike-slipThrust faultingNormalFolding &
1. Extension - Normal faulting
Fault Scarp (escarpment)from single event
From Multiple Events
Wasatch Faulting over Millions of Years: See Classroom Resource Folder
Over several million yearsSierra 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.
Block Faulting in the Basin and Range
Why is Basin & Range Extending?
Classroom ResourceSan Andreasformationstoppedcompressionand startedextension
Extension produce deep valleys filled with gravels (and water)
So much extension that the crust popped back up
Isostacydemandsthat if crustthins, the root rises up
so Camelback is just a flake off the bulge
2. compressionthrust faulting
REVERSE FAULTS: Hanging wall moves up relative to footwallResult of compression: plates collidingTwo types: low-angle or thrust faults, and high-angle reverse faultsIndividual layers can move 100s of kilometersAlps are a great example
Convergent Plate Boundaries and Thrust FaultingOcean-Oceancollision forms Island Arc: Japan,Aleutians, Cent. Am.Continent-Continentcollision formsFolded Mountain Belt:Alps, Himalayans, Appalachians
Thrust Faulting & Mountains
Lewis Thrust Fault
1971 Ms 6.6 SAN FERNANDO EARTHQUAKE1.4 m slip on 20x14 km2 faultThrust faulting from compression across Los Angeles Basin Fault had not been previously recognized65 deaths, in part due to structural failurePrompted improvements in building code & hazard mapping
$20B damage makes it the most costly earthquake to date in the U.S.S&W 4.5-9Los Angeles BasinThrust earthquakes indicate shortening1994 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 BaySandy 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