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Diastrophism Processes Breaking & Warping Earth
Faults and Folds Part 2 Diastrophism Processes Breaking & Warping Earth
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Faults and Folds Transform – Strike-slip faulting
Extension - Normal faulting (part 1) Compression - Thrust faulting (part 1) Transform – Strike-slip faulting Folding from Compression
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3. Transform – Strike-slip faulting
NORTH AMERICA 36 mm/yr PACIFIC San Andreas Fault, Carrizo Plain
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Classroom Resource
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Online Videos 1906 San Francisco Earthquake
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1906 S.F. Quake
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1989 LOMA PRIETA, CALIFORNIA EARTHQUAKE
MAGNITUDE 7.1 ON THE SAN ANDREAS Davidson et al
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Classroom Resources
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Cal Memorial Stadium
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1989 LOMA PRIETA, CALIFORNIA EARTHQUAKE
The two level Nimitz freeway collapsed along a 1.5 km section in Oakland, crushing cars Freeway had been scheduled for retrofit to improve earthquake resistance
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Houses collapsed in the Marina district of San Francisco
1989 LOMA PRIETA, CALIFORNIA EARTHQUAKE Houses collapsed in the Marina district of San Francisco Shaking amplified by low velocity landfill Stein & Wysession (USGS)
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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
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EARTHQUAKE RECURRENCE IS HIGHLY VARIABLE
Reasons are unclear: randomness, stress effects of other earthquakes on nearby faults… Extend earthquake history with paleoseismology Sieh et al., 1989 M>7 mean 132 yr s 105 yr S&W
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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 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
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San Andreas Fault Helps Set Topography
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More Dangerous: LA riddled with unknown faults
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INLAND EMPIRE Southern California San Bernardino Mountains
Cucamonga fault San Andreas fault San Jacinto fault INLAND EMPIRE Southern California
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Recent mudslide scars Cucamonga fault scarp
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Pads for 47 new homes SAN ANDREAS FAULT
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Classroom Resources Shaking Wet Sand Italy Example
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Highest Liquefaction Potential
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(adjacent to the San Andreas fault)
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Classroom Resources What will happen when a big one hits the “Inland Empire” Animation of the future quake
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Landforms of a Strike-Slip Fault
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Classroom Resource “Spin Around” QTVR at Offset Drainage, Wallace Creek, San Andreas Fault
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Strike-Slip Faulting elsewhere, too in Turkey & Levant
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Quake in Turkey
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Quake in Turkey
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4. Folding from Compression
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Faulting Relationship Between Stress and Strain at low Temps and Pressure or Sudden Stress
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Relationship Between Stress and Strain under high Temps or Pressure
Folding
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Monocline – single bend
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Single bend Flat- lying Flat- lying
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Anticline fold from:
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Folded Rocks, Hwy 23 Newfoundland, New Jersey
Adjacent Anticline and Syncline Source: Breck P. Kent
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Anticlines and Oil Early USA petroleum exploration, e.g. Pennsylvania anticlines
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Folded Rock Before Erosion
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Folds Erode Creating Flatirons (hard layers on side of anticline fold)
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Fold Erosion creates Hogbacks from a side of the fold
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Banff, Canada
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Classroom Resource QTVR “spin arounds” to see hogbacks and monoclines (Waterpocket, San Rafael Swell)
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Folded Rock After Erosion
Eroded Anticline, older rocks in center. Syncline is opposite.
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Topography may be opposite of Structure Anticline Before/After Erosion
Notice center rock oldest
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Topography may be opposite of Structure Syncline Before/After Erosion
Notice center rock youngest
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Synclinal Ridge Hard strata last preserved at the bottom of the syncline, holding up the weaker rock
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Synclinal Mountain, Canada
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Synclinal Mountain, Mt Everest
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Lazy Path of Rivers: Erode rock in the weak strata creating “strike valley”
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Namibia: Most of the streams (dry washes) flow between hogbacks
But Ugab River cuts across the hard layers (hogbacks). Why? How?
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Transverse Streams that cut right across fold belts & horsts
Why didn’t the Susquehanna River go around the fold? Why did it go through? Transverse Streams that cut right across fold belts & horsts
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How did the Columbia River get through the Cascades?
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How did this stream cross the Anticline in the Zagros Mountains?
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Overflow of an ancient lake most common explanation in the west
Ancient Lake Roosevelt Overflowed
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Lake Overflow led to Grand Canyon Formation
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Classroom Resource Modeling how streams get across uplifts
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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
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