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?
What is an earthquake?
Online Animations
Earthquake Visualizations
http://serc.carleton.edu/NAGTWorkshops/vis
ualization/collections/earthquakes.html
Fault – rocks snapped
Not always BIG
events…
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 groundshaking. 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.
2.
3.
4.
Extension - Normal faulting
Compression - Thrust faulting
Transform – Strike-slip faulting
Folding from Compression
Compression, Tension,
and Shearing Stress
Normal
Folding &
Thrust faulting
Strike-slip
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 a
Horst and Graben system. An area under tension will often have
Multiple 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
2.
compression
thrust
faulting
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
Classroom Resources
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
Los Angeles Basin
$20B damage makes it the most costly
earthquake to date in the U.S.
Thrust earthquakes
indicate shortening
1994 Northridge
Ms 6.7
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.
Downtown Seattle following the 1949 earthquake.
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.
Taiwan Thrust Faulting ‘99
Campania Italy Thrust Faulting ‘80