091107 Lecture7

Slide1: 

Sept. 11, 2007: Today’s Topics: More EQs Reading: Abbott Ch.s 4,6,7 Geos 218: Geological Disasters & Society

Slide2: 

Earthquake Main Concepts: Earthquakes Stress Faults Types of Faults Seismic Waves Seismographs Earthquake Location Earthquake Size Earthquake Hazards It’s not EQs, it’s buildings...

Building designWhich building do you want to work in and why?: 

Building design Which building do you want to work in and why? Resistance to shear is critical.

Building design: 

Building design

Building design: Avoid RESONANCE...: 

Building design: Avoid RESONANCE... Why is building damage selective?

Resonance: 

Resonance If the period of the wave matches the period of the building, shaking is amplified and resonance results. Common cause of catastrophic failure of buildings Eliminate resonance: Change height of building Move weight to lower floors Change shape of building Change building materials Change attachment of building to foundation structural engineering for seismic hazards

Elevated Highways: A Common Problem: 

Elevated Highways: A Common Problem Too much weight on concrete columns!

Seismic intensity affected by different rock types - : 

Seismic intensity affected by different rock types - Amplitude of oscillation Seismic waves passing into softer rock slow down and increase in amplitude to carry the same energy. When the SW period matches the period of the building - damage

Ground shaking: 

Ground shaking Buildings on unstable ground? Loma Prieta EQ 1989 Oakland Freeway

Liquefaction – wet sediments become “quicksand”: 

Liquefaction – wet sediments become “quicksand” Anchorage, 1964

Seismic risk in U.S.: 

Seismic risk in U.S. Expected: California, Seattle, Salt Lake City Unexpected: upstate NY, New Madrid, Charleston

Arizona Earthquakes- - -Southwestern AZ Northwestern AZ Central Mountainregion: 

Arizona Earthquakes - - - Southwestern AZ Northwestern AZ Central Mountain region 1887

Arizona Earthquakes1990-2001- - -: 

Arizona Earthquakes 1990-2001 - - -

Santa Ritas & Madera Canyon Fan: 

Santa Ritas & Madera Canyon Fan

Earthquake prediction still eludes us: 

Earthquake prediction still eludes us Which fault will break? When will it break? Size of earthquake?

Earthquake prediction is basically still just a probability game: 

Earthquake prediction is basically still just a probability game probabiliities of EQs b/4 2032 based on historic records, trenching, GPS

Slide19: 

What is meant? Comparable earthquake occurred in Alaska, 2002 on Denali fault Over 140 seconds, ruptured 340 km in magnitude 7.9 earthquake with offsets up to 8.8 m Significant directivity – triggered earthquake swarms up to 3,660 km to the southeast as far as Utah Unpopulated area, minimal effects on people The Big One

Slide20: 

1857 Fort Tejon earthquake (m=7.9) on San Andreas fault Over 130 seconds, ruptured 360 km with offsets up to 9.5 m Relatively unpopulated area at that time San Bernardino section of San Andreas fault now has 3 million people The Big One

Slide21: 

San Andreas Fault Zone

Slide22: 

San Andreas Fault Zone locked segments (sections ruptured during large eqs in 1906 and 1857) creeping segments with frequent small to moderate eqs (Parkfield) Different sections of the fault behave differently 1857 1906 1906 (M=7.8) 1857 (M=8.3)

Slide23: 

Great 1906 San Francisco Eq. (M=7.8) 430 km of San Andreas fault between Cape Mendocino and San Juan Bautista shifted up to 6 m Intense ground shaking for about one minute in early morning hours Damage much worse in areas constructed on artificial fill rather than rock or consolidated sediment Many fires broke out and water lines were destroyed, making fire-fighting impossible – fires caused ten times more damage than shaking

Slide24: 

‘locked’ section of fault

Slide25: 

1989 Loma Prieta (world series) Eq. (M=6.9) Occurred at the fault bend near Santa Cruz Mountains Slip was not just horizontal Loma Prieta region was a seismic gap before eq.

Slide26: 

67 killed 3,757 injured 12,000 homeless $6 billion lost Damage was mostly to poorly sited or designed structures REMEMBER: Earthquakes don’t kill, buildings do !!!

Slide27: 

M = 6.0 Parkfield Earthquakes Long awaited 2004 Event !!! Drilling inside the fault !!!

Slide28: 

Compression where San Andreas bends Compression creates thrust faults that uplift mountains nearby Shortening near LA can generate M=6 eq. every six years

Slide29: 

Los Angeles San Andreas Fault 1971 San Fernando & 1994 Northridge Eqs. M=6.9 M=6.7

Slide30: 

Los Angeles San Andreas Fault

Slide31: 

1994 Northridge Earthquake Pico blind thrust ruptured in magnitude 6.7 earthquake under Northridge (shaking fortunately directed away from Los Angeles) 61 people killed, 9,000 people injured, $20 billion in damages Similar to 1971 San Fernando Valley earthquake except shaking directed toward Los Angeles Outbreak of Valley Fever Landslides

Slide32: 

U.S. Earthquakes 1899-1990 Earthquakes occur throughout North America, not just in California Occur in clusters, mostly in western North America but also in eastern North America and Hawaii Pacific NW - Cascades San Andreas Fault Alaska & Hawaii Eastern California - Western Nevada Yellowstone Hotspot Eastern Basin & Range - Wastach Front Rocky Mountains Rio Grande Rift

Slide33: 

Physiographic provinces of western US Locate: Great Valley Snake River Plain Great Salt Lake Rocky Mtns The Basin and Range Colorado Plateau Salton Sea/Imperial valley Rio Grande rift

Western North America- - - The Basin & Range- - -A region where the continent is being pulled apart – extended... Distance from SLC to SFO has doubled in last 25 million years!: 

Western North America - - - The Basin & Range - - - A region where the continent is being pulled apart – extended ... Distance from SLC to SFO has doubled in last 25 million years!

Basin & Range: 

Basin & Range

Basin & Range Fault Models: 

Basin & Range Fault Models

active EQ zones in the Basin & Range: 

active EQ zones in the Basin & Range intermountain seismic belt western Great Basin seismic trend

Slide38: 

Fault Scarp from the 1915 mag 7.1 earthquake in Pleasant Valley, Nevada

Intermountain seismic belt: 

Intermountain seismic belt Western MT Yellowstone ID - WY border SLC (Wasatch Front) SW Utah North-trending curve 1,500 km long and 100-200 km wide separating Basin and Range from Colorado Plateau and Rocky Mountains

The Wasatch FrontBoundary between Basin and Range and Wasatch Range: 

The Wasatch Front Boundary between Basin and Range and Wasatch Range Capable of large EQs Last major EQ ~1600 AD 1.5 million people at fault

Slide41: 

This exaggerated 3D view of the Wasatch Front, from Utah Valley to the Salt Lake Valley, gives you a sense of the abrupt nature and topography of fault-block mountains. (Digital maps produced by Eric H. Christiansen)

Photo of exposure of the Wasatch Fault scarp. This is one of the best exposures anywhere along the 240 mile fault. Large earthquakes occur along the fault on average about every 350 years. This Provo segment of the fault last ruptured about the year 1400. (Photo by Bill Harris): 

Photo of exposure of the Wasatch Fault scarp. This is one of the best exposures anywhere along the 240 mile fault. Large earthquakes occur along the fault on average about every 350 years. This Provo segment of the fault last ruptured about the year 1400. (Photo by Bill Harris)

Slide43: 

Intermountain Belt: Utah, Idaho, Wyoming, Montana Borah Peak, Idaho, 1983 Lost River fault ruptured in 7.3 earthquake Borah Peak (Idaho’s highest point) 0.3 m higher, Thousand Springs Valley few meters lower Ground shaking caused fountains of groundwater http://quake.wr.usgs.gov/research/deformation/modeling/papers/naturalhistory/naturalhistory

Slide44: 

Intermountain Belt: Utah, Idaho, Wyoming, Montana Hebgen Lake, Montana, 1959 Two faults moved within five seconds of each other with magnitude 6.3 and 7.5 earthquakes Created landslide that dammed canyon and formed Earthquake Lake Dropped north end of Hebgen Lake 7-8 m, creating seiche that sloshed back and forth for almost 12 hours

Slide45: 

difficult-to-explain earthquakes

Slide46: 

1811-1812 New Madrid huge “felt” area many events, several very large lots of liquefaction paleoseismology shows big EQs here in 500, 900, 1300, 1600... USGS says 90% probability of magnitude 6-7 EQ there in next 50 yrs WHY THERE?

FIG. 6.25: 

FIG. 6.25 1886 Charleston, South Carolina Earthquake Massive earthquake in 1886 destroyed 90% of buildings No surface faulting from earthquake Below surface studies indicate at least five similar earthquakes in last 3,000 years – recurrence interval of about 600 years