earthquake case histories subduction zone tectonics epicenter in prince william sound alaska 1964:...

EARTHQUAKE CASE HISTORIESSUBDUCTION ZONE TECTONICS

Epicenter in Prince William sound

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.


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




DESTRUCTION FROM….

1.) avalanche2.) tsunami3.) landslide4.) liquefaction

PACKAGE DEAL


Mexico City 1985

Cocos Plate subducting under the N.A. plate

Magnitude 8.1

Epicenter Location

Overhead Fig. 4.4

Notice seismic gaps


Mexico City 1985

Collapsed General Hospital, Mexico City, Mexico(Courtesy USGS DDS21)


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




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


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???…




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


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


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





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



BRIDGE FAILURE=PROBLEMS??



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


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


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


Borah Peak, Idaho 1983

Location



1.) 7.3 mag (10 mi. deep)2.) 9 foot displacement3.) Normal faults4.) Borah Peak “grew” by 1 foot



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


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.




PROBLEMS1.) Mississippi Embayment=lots of sandy/mudy

water soakedsediments

2.) Amplification, liquifaction

3.) Large population

4.) Oh yeah they tend to BIG!!!!

earthquake case histories subduction zone tectonics epicenter in prince william sound alaska 1964:...

Documents

plate overhead

seconds30 story

seconds5 story

pacific plate

cocos plate subducting

fuca plate subducting

seismic gapsort

story building affected2