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