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Faults and Folds Part A. Diastrophism Processes Breaking & Warping Earth. Faults and Folds Part A. Extension - Normal faulting (Part A) Compression - Thrust faulting (Part A) Transform – Strike-slip faulting (Part B) Folding from Compression (Part B). What is a fault? .
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Faults and FoldsPart A Diastrophism Processes Breaking & Warping Earth
Faults and FoldsPart A • Extension - Normal faulting (Part A) • Compression - Thrust faulting (Part A) • Transform – Strike-slip faulting (Part B) • Folding from Compression (Part B)
What is a fault? What is an earthquake?
Online Animations Earthquake Visualizations http://serc.carleton.edu/NAGTWorkshops/visualization/collections/earthquakes.html
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.
Faults and Folds • Extension - Normal faulting • Compression - Thrust faulting • Transform – Strike-slip faulting • Folding from Compression
Compression, Tension, and Shearing Stress Normal Strike-slip Folding & Thrust faulting
Wasatch Faulting over Millions of Years: See Classroom Resource Folder
Over several million years Sierra Nevada
Triangular Facets – produced by erosion of the fault scarp by river valleys
Alternating normal faults lead to a characteristic pattern called a Horst and Graben system. An area under tension will often have Multiple mountain ranges as a result.
Classroom Resource San Andreas formation stopped compression and started extension
REVERSE FAULTS: Hanging wall moves up relative to footwall Result of compression: plates colliding Two types: low-angle or thrust faults, and high-angle reverse faults Individual layers can move 100’s of kilometers Alps are a great example
Dezes, U. of Lausanne Edwards & Kidd, U. of Albany Thrust Faulting & Mountains
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
Los Angeles Basin Thrust earthquakes indicate shortening 1994 Northridge Ms 6.7 $20B damage makes it the most costly earthquake to date in the U.S. S&W 4.5-9
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.
Cultus Bay Scatchet Head Sandy Hook As the floor of the Puget Sound was vertically offset, a tsunami was generated that inundated several 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.
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.
