EARTHQUAKE CASE HISTORIES SUBDUCTION ZONE TECTONICS
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EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS
Epicenter in Prince William sound
ALASKA 1964: Good Friday Earthquake
EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS
ALASKA 1964: Good Friday Earthquake
1.) Pacific Plate Under North American Plate
2.) Strong ground motion for 3-4 minutes
3.) Downward thrusts followed at 9, 19, 28, 29,4, and 72 sec. later
Hand written notes on setting.
EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS
Alaska 106 $84 million
British Columbia
0 $10 million
Washington 0 minor coastal damage
Oregon 4 $0.7 million
California 13 $10 million
COSTS IN 1964 DOLLARS
131 killed, 122 from Tsunami
ALASKA 1964: Good Friday Earthquake
EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS
ALASKA 1964: Good Friday Earthquake
DESTRUCTION FROM….
1.) avalanche2.) tsunami3.) landslide4.) liquefaction
PACKAGE DEAL
EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS
Mexico City 1985
Cocos Plate subducting under the N.A. plate
Magnitude 8.1
Epicenter Location
Overhead Fig. 4.4
Notice seismic gaps
EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS
Mexico City 1985
Collapsed General Hospital, Mexico City, Mexico(Courtesy USGS DDS21)
EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS
Mexico City 19851.) 6-16 story building affected
2.) Resonant frequency/period(1-2sec)same(=) seismic waves(1-2sec)
3.) Lake deposits amplified waves
4.) Coastal villages little damage?WHY?
Building Height
Natural Period
2 story .2 seconds
5 story .5 seconds
10 story 1.0 seconds
20 story 2.0 seconds
30 story 3.0 seconds
EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS
Cascadia Subduction Zone
1.) 750 miles long
2.) youthful ocean slab resists subduction = build upof elastic energy
3.) Juan de Fuca plate subducting under N.A. plate
Overhead Fig. 4.8
EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS
1.) About 200 years since last major major event.
2.) Is it “plugged” and subduction stopped?
3.) Volcano activity tell us no.
4.) Is subduction happening smoothly? Probably not
5.) What is the worry???…
Cascadia Subduction Zone
EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS
Cascadia Subduction Zone
Lets consider the past
Last Super Big Quake Jan. 26, 1700
How do we know?1.) Tree rings from flooded trees
that died (ND pg. 104/Fig. 4.11)-subsidence
2.) Japanese records have a tsunamihitting midnight-dawn
suggests a Jan. 26 1700 EQ at this location
HAPPENED ONCE CAN HAPPEN AGAIN
EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS
Seattle Feb. 28, 2001
1.) 6.98 mag.2.) Focus/hypocenter 33 miles deep WHY?3.) epicenter 35 mi. SW of Seattle4.) $2 BILLION in damage5.) 320 hurt but no deaths (lucky)6.) since 1970’s EQ code has been in use7.) Spce needle 600’ high,
built to withstand 9.1.
Why brick failure?
EARTHQUAKE CASE HISTORIESTRANSFORM ZONE TECTONICS
CALIFORNIA - San Andreas Fault
1.) 750 miles long - parallel faults (complex system)
2.) Some sections have creeping motion and others are locked (seismic gap) (ND pg. 109/fig. 4.16)
San Francisco 1906
a) ~ 20 ft horizontal motion over up to 265 milesb) mag. 8 60 seconds durationc) wood faired better BUT fire significant type of destructiond) Today - S.F. is a seismic gap-sort of-some activity
EARTHQUAKE CASE HISTORIESTRANSFORM ZONE TECTONICS
Loma Prieta 1989 (World Series)a) mag 7.1 11 sec durationb) 67 dead - most from freeway collapsec) marina district suffered damage due to
artificial fill - saturated in manycases (liquifaction)
d.) 18 km deepe.) 11 secs. of shakingf.) 6ft horizontalg.) 4ft. vert.h.) had been seismic gap
EARTHQUAKE CASE HISTORIESTRANSFORM ZONE TECTONICS
CALIFORNIA - San Andreas Fault
EARTHQUAKE CASE HISTORIESTRANSFORM ZONE TECTONICS
CALIFORNIA - San Andreas Fault
Loma Prieta 1989Candlestick park Giants homefield advantage?
LIQUIFACTION (again)
Loma Prieta 1989 (World Series)a) mag 7.1 11 sec durationb) 67 dead - most from freeway collapsec) marina district suffered damage due to
artificial fill - saturated inmany cases (liquifaction)
d.) freeways built on muds hadresonant frequency
EARTHQUAKE CASE HISTORIESTRANSFORM ZONE TECTONICS
CALIFORNIA - San Andreas Fault
BRIDGE FAILURE=PROBLEMS??
EARTHQUAKE CASE HISTORIESTRANSFORM ZONE TECTONICS
CALIFORNIA - San Andreas Fault
Loma Prieta 1989Much of the marina district is buld on artificial fill from the 1906 quake
LIQUIFACTION RESULTS (again)Marina district
“soft” first stories for parking cars along withliquifaction=that
EARTHQUAKE CASE HISTORIESTRANSFORM ZONE TECTONICS
Common Patterns for Bay Area Quakes
1.) Common large quakes (6-7) rather than rare large >8
2.) East-west pairings
3.) Northward progression of quakes- ND pg. 118/fig. 4.33
EARTHQUAKE CASE HISTORIESINTERMOUNTAIN SEISMIC BELTDIVERGENT BOUNDARY
1.) Zone of tension=pulling apart2.) Tensional stress and strain
UTAH
IDAHO
WYO
EARTHQUAKE CASE HISTORIESINTERMOUNTAIN SEISMIC BELTDIVERGENT BOUNDARY
Hegben Lake (Near Yellowstone) 1959
1.) 6.3-7.5 mag.2.) up to 26’ of displacement3.) Normal faults-tension-pulling apart.4.) Killer big landslide5.) Madison River Dammed 53 meters deep
EARTHQUAKE CASE HISTORIESINTERMOUNTAIN SEISMIC BELTDIVERGENT BOUNDARY
Borah Peak, Idaho 1983
Location
EARTHQUAKE CASE HISTORIESINTERMOUNTAIN SEISMIC BELTDIVERGENT BOUNDARY
Borah Peak, Idaho 1983
1.) 7.3 mag (10 mi. deep)2.) 9 foot displacement3.) Normal faults4.) Borah Peak “grew” by 1 foot
EARTHQUAKE CASE HISTORIESINTERMOUNTAIN SEISMIC BELTDIVERGENT BOUNDARY
Borah Peak, Idaho 1983
Thousand Springs Valley
1.) Ground water volcanos carry sediment/sand to surface
2.) 10-20 ft fountains
EARTHQUAKE CASE HISTORIESINTRAPLATE EARTHQUAKES
New Madrid, Missouri Dec. 16, 1811
Buried rift=Reelfoot Riftfailed splitting=lots o’ cracks=Earthquakes
New Madrid, Missouri Dec. 16, 1811
1.) Largest group of clustered events EVER in US
2.) Sand volcanos
3.) Formed two new lakes=subsidence1.) Lake St. Fancis (37 mi./.62mi)2.) Reelfoot Lake (19mi/7mi.)3.) ND pg. 140/fig. 5.15)
4.) Mississipi river had waterfalls where itused to be flat=scarp
5.) Bells rang along eastern seaboard.
EARTHQUAKE CASE HISTORIESINTRAPLATE EARTHQUAKES
EARTHQUAKE CASE HISTORIESINTRAPLATE EARTHQUAKES
New Madrid, Missouri Dec. 16, 1811
PROBLEMS1.) Mississippi Embayment=lots of sandy/mudy
water soakedsediments
2.) Amplification, liquifaction
3.) Large population
4.) Oh yeah they tend to BIG!!!!