1. EARTHQUAKE CASE HISTORIES
SUBDUCTION ZONE TECTONICS
ALASKA 1964: Good Friday Earthquake
Epicenter in Prince William sound

2. EARTHQUAKE CASE HISTORIES
SUBDUCTION 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.

3. EARTHQUAKE CASE HISTORIES SUBDUCTION ZONE TECTONICS
ALASKA 1964: Good Friday Earthquake
131 killed, 122 from Tsunami
COSTS IN 1964 DOLLARS
Alaska
106
$84 million
British Columbia
$10 million
Washington
minor coastal damage
Oregon 4
$0.7 million
California 13

4. EARTHQUAKE CASE HISTORIES
SUBDUCTION ZONE TECTONICS
ALASKA 1964: Good Friday Earthquake
DESTRUCTION FROM….
1.) avalanche
2.) tsunami
3.) landslide
4.) liquefaction
PACKAGE DEAL

5. Cocos Plate subducting under the N.A. plate
EARTHQUAKE CASE HISTORIES
SUBDUCTION 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

6. Collapsed General Hospital, Mexico City, Mexico (Courtesy USGS DDS21)
EARTHQUAKE CASE HISTORIES
SUBDUCTION ZONE TECTONICS
Mexico City 1985
Collapsed  General Hospital, Mexico City, Mexico (Courtesy USGS DDS21)

7. Mexico City 1985 EARTHQUAKE CASE HISTORIES SUBDUCTION ZONE TECTONICS
1.) 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

8. Cascadia Subduction Zone
EARTHQUAKE CASE HISTORIES
SUBDUCTION ZONE TECTONICS
Cascadia Subduction Zone
1.) 750 miles long
2.) youthful ocean slab resists subduction = build up
of elastic energy
3.) Juan de Fuca plate subducting under N.A. plate
Overhead Fig. 4.8

9. Cascadia Subduction Zone
EARTHQUAKE CASE HISTORIES
SUBDUCTION ZONE TECTONICS
Cascadia Subduction Zone
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???…

10. Cascadia Subduction Zone
EARTHQUAKE CASE HISTORIES
SUBDUCTION 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 tsunami
hitting midnight-dawn
suggests a Jan EQ at this location
HAPPENED ONCE CAN HAPPEN AGAIN

11. 2.) Focus/hypocenter 33 miles deep WHY?
EARTHQUAKE CASE HISTORIES
SUBDUCTION ZONE TECTONICS
Seattle Feb. 28, 2001
1.) 6.98 mag.
2.) Focus/hypocenter 33 miles deep WHY?
3.) epicenter 35 mi. SW of Seattle
4.) $2 BILLION in damage
5.) 320 hurt but no deaths (lucky)
6.) since 1970’s EQ code has been in use
7.) Spce needle 600’ high,
built to withstand 9.1.
Why brick failure?

12. EARTHQUAKE CASE HISTORIES
TRANSFORM 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)

13. EARTHQUAKE CASE HISTORIES
TRANSFORM ZONE TECTONICS
San Francisco 1906
a) ~ 20 ft horizontal motion over up to 265 miles
b) mag seconds duration
c) wood faired better BUT fire significant type of destruction
d) Today - S.F. is a seismic gap-sort of-some activity

14. EARTHQUAKE CASE HISTORIES
TRANSFORM ZONE TECTONICS
CALIFORNIA - San Andreas Fault
Loma Prieta 1989 (World Series)
a) mag sec duration
b) 67 dead - most from freeway collapse
c) marina district suffered damage due to
artificial fill - saturated in many
cases (liquifaction)
d.) 18 km deep
e.) 11 secs. of shaking
f.) 6ft horizontal
g.) 4ft. vert.
h.) had been seismic gap

15. EARTHQUAKE CASE HISTORIES
TRANSFORM ZONE TECTONICS
CALIFORNIA - San Andreas Fault
Loma Prieta 1989
Candlestick park Giants homefield advantage?
LIQUIFACTION (again)

16. EARTHQUAKE CASE HISTORIES
TRANSFORM ZONE TECTONICS
CALIFORNIA - San Andreas Fault
Loma Prieta 1989 (World Series)
a) mag sec duration
b) 67 dead - most from freeway collapse
c) marina district suffered damage due to
artificial fill - saturated in
many cases (liquifaction)
d.) freeways built on muds had
resonant frequency
BRIDGE FAILURE=PROBLEMS??

17. LIQUIFACTION RESULTS (again)
EARTHQUAKE CASE HISTORIES
TRANSFORM ZONE TECTONICS
CALIFORNIA - San Andreas Fault
Loma Prieta 1989
Much 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 with
liquifaction=that

18. EARTHQUAKE CASE HISTORIES
TRANSFORM 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

19. EARTHQUAKE CASE HISTORIES
INTERMOUNTAIN SEISMIC BELT
DIVERGENT BOUNDARY
1.) Zone of tension=pulling apart
2.) Tensional stress and strain
IDAHO
WYO
UTAH

20. EARTHQUAKE CASE HISTORIES
INTERMOUNTAIN SEISMIC BELT
DIVERGENT BOUNDARY
Hegben Lake (Near Yellowstone) 1959
1.) mag.
2.) up to 26’ of displacement
3.) Normal faults-tension-pulling apart.
4.) Killer big landslide
5.) Madison River Dammed 53 meters deep

21. EARTHQUAKE CASE HISTORIES
INTERMOUNTAIN SEISMIC BELT
DIVERGENT BOUNDARY
Borah Peak, Idaho 1983
Location

22. EARTHQUAKE CASE HISTORIES
INTERMOUNTAIN SEISMIC BELT
DIVERGENT BOUNDARY
Borah Peak, Idaho 1983
1.) 7.3 mag (10 mi. deep)
2.) 9 foot displacement
3.) Normal faults
4.) Borah Peak “grew” by 1 foot

23. EARTHQUAKE CASE HISTORIES
INTERMOUNTAIN SEISMIC BELT
DIVERGENT BOUNDARY
Borah Peak, Idaho 1983
Thousand Springs Valley
1.) Ground water volcanos carry sediment/sand to surface
2.) ft fountains

24. EARTHQUAKE CASE HISTORIES
INTRAPLATE EARTHQUAKES
New Madrid, Missouri Dec. 16, 1811
Buried rift=Reelfoot Rift
failed splitting=
lots o’ cracks=
Earthquakes

25. EARTHQUAKE CASE HISTORIES
INTRAPLATE EARTHQUAKES
New Madrid, Missouri Dec. 16, 1811
1.) Largest group of clustered events EVER in US
2.) Sand volcanos
3.) Formed two new lakes=subsidence
1.) Lake St. Fancis (37 mi./.62mi)
2.) Reelfoot Lake (19mi/7mi.)
3.) ND pg. 140/fig. 5.15)
4.) Mississipi river had waterfalls where it
used to be flat=scarp
5.) Bells rang along eastern seaboard.

26. EARTHQUAKE CASE HISTORIES
INTRAPLATE EARTHQUAKES
New Madrid, Missouri Dec. 16, 1811
PROBLEMS
1.) Mississippi Embayment=lots of sandy/mudy
water soakedsediments
2.) Amplification, liquifaction
3.) Large population
4.) Oh yeah they tend to BIG!!!!