Faulting landforms from side-by-side (transform) motion

Strike-slip faulting and landforms

PACIFIC

NORTH AMERICA

San Andreas Fault, Carrizo Plain

36 mm/yr

Transform – Strike-slip faulting

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

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., 1989

Extend 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

Highest LiquefactionPotential

(adjacent to the San Andreas fault)

Landforms of a Strike-Slip Fault

Strike-Slip Faulting elsewhere, too in Turkey & Levant

Quake in Turkey

Quake in Turkey

Ancient San

Andreas-like Fault

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.