Faults and Folds Part 2 Diastrophism Processes Breaking & Warping Earth.
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Transcript of Faults and Folds Part 2 Diastrophism Processes Breaking & Warping Earth.
Faults and FoldsPart 2
Diastrophism Processes
Breaking & Warping Earth
Faults and Folds• Extension - Normal faulting (part 1)• Compression - Thrust faulting (part 1)
• Transform – Strike-slip faulting
• Folding from Compression
PACIFIC
NORTH AMERICA
San Andreas Fault, Carrizo Plain
36 mm/yr
3. Transform – Strike-slip faulting
Classroom Resource
Online Videos
1906 San Francisco Earthquake
http://serc.carleton.edu/NAGTWorkshops/visualization/collections/SanFran1906.html
1906 S.F. Quake
1989 LOMA PRIETA, CALIFORNIA EARTHQUAKEMAGNITUDE 7.1 ON THE SAN ANDREAS
Davidson et alDavidson et al
Classroom Resources
Cal Memorial Stadium
1989 LOMA PRIETA, CALIFORNIA
EARTHQUAKE
The two level Nimitz freeway collapsed
alonga 1.5 km section in
Oakland, crushing cars
Freeway had been scheduled for retrofit
to improve earthquake resistance
1989 LOMA PRIETA, CALIFORNIA EARTHQUAKE
Houses collapsed in the Marina district of San
Francisco
Shaking amplified by low velocity landfill
Stein & Wysession 2003 2.4-10 (USGS)
Over time, slip in earthquakes adds up and reflects the plate motion
Offset fence showing 3.5 m of left-lateral strike-slip motion along San Andreas fault in 1906 San Francisco
earthquake
~ 35 mm/yr motion between Pacific and North American plates along San
Andreas shown by offset streams & GPS
Expect earthquakes on average every ~ (3.5 m )/ (35 mm/yr) =100 years
Turns out more like 200 yrs because not all motion is on the San Andreas
Moreover, it’s irregular rather than periodic
EARTHQUAKE RECURRENCE IS HIGHLY VARIABLEReasons are unclear: randomness, stress effects of other earthquakes on
nearby faults…
M>7 mean 132 yr 105 yr
Sieh et al., 1989Extend earthquake history with paleoseismology
S&W 1.2-15
In general, the most destructive earthquakes occur where large populations live near plate boundaries. The highest property losses occur in developed nations where more property is at risk, whereas fatalities are highest in developing nations.
Estimates are that the 1990 Northern Iran shock killed 40,000 people, and that the 1988 Spitak (Armenia) earthquake killed 25,000. Even in Japan, where modern construction practices reduce earthquake damage, the 1995 Kobe earthquake caused more than 5,000 deaths and $100 billion of damage. On average during the past century earthquakes have caused about 11,500 deaths per year.
The earthquake risk in the United States is much less than in many other countries because large earthquakes are relatively rare in most of the U.S. and because of earthquake-resistant construction
San Andreas
Fault
Helps Set
Topography
More Dangerous: LA
riddled with unknown faults
San Bernardino Mountains
San Andreas fault
San Jacinto fault
Cucamonga fault
Recent mudslide scars
Cucamonga fault scarp
SAN ANDREAS FAULT
Pads for 47 new homes
Classroom Resources
Shaking Wet Sand Italy Example
Highest LiquefactionPotential
(adjacent to the San Andreas fault)
Classroom Resources
What will happen when a big one hits the “Inland Empire”
Animation of the future quake
Landforms of a Strike-Slip Fault
Classroom Resource
“Spin Around” QTVR at Offset Drainage, Wallace Creek, San Andreas Fault
Strike-Slip Faulting elsewhere, too in Turkey & Levant
Quake in Turkey
Quake in Turkey
4. Folding from Compression
Relationship Between Stress and Strain at low Temps and Pressure or Sudden Stress
Faulting
Relationship Between Stress and Strain under high Temps or Pressure
Folding
Monocline – single bend
Flat- lying
Flat- lying
Single bend
Anticline fold
from: http://earth.leeds.ac.uk/learnstructure/index.htm
Folded Rocks, Hwy 23 Newfoundland, New Jersey
Source: Breck P. Kent
Adjacent Anticline and Syncline
Anticlines and Oil
Early USA petroleum exploration, e.g. Pennsylvania anticlines
Folded Rock Before Erosion
Folds Erode Creating Flatirons (hard layers on side of anticline fold)
Fold Erosion creates
Hogbacksfrom a side of the fold
Banff, Canada
Classroom Resource
QTVR “spin arounds” to see hogbacks and monoclines (Waterpocket, San Rafael Swell)
Folded Rock After Erosion
Eroded Anticline, older rocks in center. Syncline is opposite.
Topography may be opposite of Structure
Anticline Before/After Erosion
Notice center rock oldest
Topography may be opposite of Structure
Syncline Before/After Erosion
Notice center rock youngest
Synclinal Ridge
Hard strata last preserved at the bottom of the syncline, holding up the weaker rock
Synclinal Mountain, Canada
Synclinal Mountain, Mt Everest
Lazy Path of Rivers: Erode rock in the weak strata creating “strike valley”
Namibia: Most of the streams (dry washes) flow between hogbacks
But Ugab River cuts across the hard layers (hogbacks). Why? How?
Why didn’t the Susquehanna River go around the fold? Why
did it go through?
Transverse Streams that cut right across fold belts & horsts
How did the Columbia River get through the Cascades?
How did this stream cross the Anticline in the Zagros Mountains?
Overflow of an ancient lake most common explanation in the west
Ancient Lake Roosevelt Overflowed
Lake Overflow led to Grand Canyon Formation
Classroom ResourceModeling how streams get across uplifts
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