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Unformatted text preview: 22: Natural Hazards 2
Earthquakes & Tsunamis Earthquakes: largest Mexico
1985 Kobe, Japan, 1995 Indian
2004 Hazards 2: 1 Armenia, 1999 Northridge, CA, 1994 Hazards 2: 2 Earthquake damage: offsets
Fig. 10.1 Fig. 10.6
Hazards 2: 3 Hazards 2: 4 3-meter offset of fence near Bolinas, CA, produced
by 1906 San Francisco earthquake.
Photo: G.K. Gilbert Earthquake damage: shaking EQ damage: shaking Fig. 10.27 Photo: California St. Univ. Freeway collapse, 1995 Kobe, Japan,
earthquake. Photo: Reuters/Corbis Surface waves
Hazards 2: 5 Earthquake damage: shaking
(a) Concrete-slab or steel
supports disconnect and
collapse Hazards 2: 6 Fig. 10.28 Earthquake damage: shaking
(e) Neighboring buildings
collide and shatter;
floors inside a tall
building may collapse (b) Building’s façade falls off
Building’ (c) Poorly supported bridge
collapses (d) Bridge span disconnects and
Hazards 2: 7 (f) Concrete-block, brick
or adobe buildings
crack apart and
(g) Steep cliff collapses,
carrying buildings with
it Hazards 2: 8 Fig. 10.28 Earthquake damage: fires Earthquake damage: fire • Caused by ruptured gas lines (ruptured water lines add
to problem) • San Francisco, 1906: most deaths caused by fire Fig. 10.33 Fig. 10.25 Photo: AP
Hazards 2: 9 Hazards 2: 10 Earthquake damage: Tsunamis Earthquake damage
• Liquefaction: shaking turns water-saturated sediment into
quicksand; cannot support any structures built on it Fig. 10.32 Fig. 10.34
Hazards 2: 11 Hazards 2: 12 Earthquake damage Earthquake damage: landslides • Liquefaction: shaking turns water-saturated sediment into
quicksand; cannot support any structures built on it
earthquake. Fig. 10.31 Photo: P.L.
Kresan Hazards 2: 13 Earthquake damage: landslides Hazards 2: 14 Review Questions
22-1. The magnitude of the largest earthquake recorded this century is ___.
22-2. A. True / B. False: The earthquake with the highest death toll also had the
22-3. A. True / B. False: Only surface waves cause earthquake damage.
22-4. A. True / B. False: Virtually all of the deaths caused by the 1906 San Francisco
earthquake occurred because poorly constructed buildings collapsed. 1964 Alaska Earthquake. Photo: NGDC
Hazards 2: 15 22-5. Which of the following is a type of damage related to earthquakes?
A. Offsets of the land surface and shaking.
B. Fires caused by ruptured gas lines.
C. Landslides and liquefaction.
E. All of the above.
Hazards 2: 16 Amount of damage depends on: Amount of damage depends on:
5. Nature of substrate 1. Magnitude
2. Depth below the
surface… --Solid rock: shakes only during passage of earthquake waves
--Thick soils or unconsolidated sediment: 3. Proximity to
4. Style & quality
of construction Fig. 10.30b See Table
Hazards 2: 17 Hazards 2: 18 Amount of damage depends on: Predicting location of earthquakes
• At or near plate boundaries
1. Divergent plate boundaries: shallow-focus; low- to moderate
damage--ridges are long, faults are ____
(no longer than distance between transforms) 6. Topography: Fig. 4.17 Fig. 10.30a California coast;
1994 Northridge earthquake
Hazards 2: 19 Hazards 2: 20 Fig. 10.20 Predicting location of earthquakes Predicting location 2. Conservative plate boundaries: shallow-focus; moderate to high
damage--some faults (San Andreas) are ________. 3. Convergent plate boundaries:
shallow- to deep-focus; high to
severe damage--fault zones
(subduction zones) are… Fig. 10.25 Fig. 10.20 Hazards 2: 21 Predicting location of earthquakes
• Within plates: moderate-high hazard…
• Volcanoes Fig. 10.20
Hazards 2: 23 Hazards 2: 22 Predicting location of earthquakes
• Identify faults or fault zones Fig. 10.xx
Hazards 2: 24 Long-term prediction
• The past is the key to the future
• Seismic-hazard maps Long-term prediction
Fig. 10.40a • The past is the key to the future
• Seismic-hazard maps Highest hazard Lowest hazard Lowest probability Highest probability Hazards 2: 25 Long-term prediction Fig. 10.40b Hazards 2: 26 Long-term prediction Recurrence interval: average time between quakes based on historical
records and geologic record of disruptions produced by shaking Disrupted layer (1)
contains wood dated
at 900 years ago, and
is overlain by an
undisrupted layer with
wood dated at 800
years ago. Earthquake
occurred between 900
and 800 years ago;
average is 850 years 800 yr
900 yr Fig. 10.39
Hazards 2: 27 Fig. 10.39
Hazards 2: 28 Long-term prediction Long-term prediction
Faulted paleosol (2)
contains wood dated
at 750 years ago, and
is overlain by an
unfaulted layer with
wood dated at 650
years ago. Earthquake
occurred between 750
and 650 years ago;
average is 700 years 500 yr 750 yr 400 yr Sand volcanoes (3)
earthquake. Wood in
layer above source
layer is 500 yrs old.
Wood in layer covering
sand volcanoes is 400
yrs old. Earthquake
occurred between 500
and 400 years ago;
average is 450 years 650 yr
750 yr Fig. 10.39 Fig. 10.39 Hazards 2: 29 Hazards 2: 30 Long-term prediction
275 yr Long-term prediction
250 yr Tree (4) started
growing 275 years ago,
but asymmetric tree
rings start at 250 years
ago. Earthquake 250
years ago caused tree
to tilt. Q1. What is the average
A. 150 yrs
B. 200 yrs
C. 250 yrs 250 yr 200 yr
700 yr 250 yr 150 yr
850 yr Fig. 10.39
Hazards 2: 31 Fig. 10.39
Hazards 2: 32 Long-term prediction Long-term prediction
Q2. A. True / B. False: An
earthquake is overdue because
the time since the last
earthquake is larger than the
average recurrent interval. 250 yr Seismic gaps: parts of an active fault that have not slipped in a long time… Fig. 10.40d 200 yr
700 yr 250 yr 150 yr
850 yr No longer a gap Fig. 10.39
Hazards 2: 33 Hazards 2: 34 Short-term prediction Short-term prediction (not yet reliable) Stress triggering: earthquakes relieve stress on one fault (or part of a fault)
and raise stress on another fault (or part of a fault) Fig. 10.42
North Anatolian fault:
from east to west Gap
Hazards 2: 35 • Foreshocks: small
precede a larger
likely related to
cracking of stressed
• Change in water
levels of wells,
changes in electrical
conductivity Fig. 10.41 Gap
Hazards 2: 36 Minimizing damage & casualties Minimizing damage & casualties 1. In earthquake belts, build structures that can sway & bounce; use
extra bolts, fasteners, and cross beams; avoid brick & mortar; wood
2. Install auto-gas shutoffs; know location of gas & electric shutoffs 3. Fasten (book)cases to walls
4. Avoid building on slopes,
5. Seek safety outside or beneath
a sturdy table, doorframe
6. Have first-aid kit, emergency
food and water supplies,
flashlight, radio available Fig.
10.43 Fig. 10.28
Photo: California St. Univ. Fig. 10.44 Fig.
10.28 Review Questions
22-6. Which earthquake intensity scale assesses the effects of an earthquake on
humans and human-made structures?
A. Richter scale
B. Mercalli scale
22-7. A. True / B. False: Earthquakes that occur at deeper depths always cause more
damage than earthquakes that occur at shallow depths.
22-8. A. True / B. False: Divergent plate boundaries are not associated with high
seismic hazard because the depth of earthquakes is shallow and the length of the
faults is long, spreading the risk over a much larger region.
22-9. A. True / B. False: Convergent plate boundaries are associated with high to
extreme seismic hazard because subduction zones are deep and long.
22-10. ___ plate boundaries are typically associated with the largest, deadliest quakes.
D. Hot spot
22-11. Medium- and deep-focus earthquakes occur along ____________.
A. convergent plate boundaries B. divergent plate boundaries
C. transform plate boundaries
D. all three major types of plate boundaries
22-12. A. True / B. False: Earthquakes only occur at plate boundaries. Review Questions
22-13. A. True / B. False: The earthquake risk in New Jersey is lower than in California
because there are no faults in New Jersey.
22-14. Long-term prediction of earthquake behavior ____________.
A. is based on past earthquake activity
B. works on the principle that zones of past seismicity will be active in the future
C. includes the notion of seismic gaps—places where an earthquake is overdue
D. all of the above
22-15. Which of the following is least correct?
A. For faults with a history of repeated earthquakes, earthquake hazard is high on
faults that have not had an earthquake in a time period that is longer than the
B. Earthquake hazard is greater on faults or parts of faults that are adjacent to a fault
or part of a fault that has slipped (has experienced an earthquake).
C. Earthquake hazard is lesser in areas of seismic gaps compared to other areas.
22-16. Which of the following is least correct?
A. All other things being equal, it is better to build on solid rock than thick soils or
B. For relatively small buildings, it is better to build with bricks than wood.
C. All other things being equal, it is better to build on gentle slopes compared to
steep slopes. Tsunamis Tsunamis Giant waves that are higher and extend farther inland than windcaused waves Giant waves that are higher and extend farther inland than windcaused waves Kodiak, Alaska, 1964 Hilo, Hawaii Tsunamis: characteristics Tsunamis: differences with wind waves Open ocean
Height: <0.4 m
Wavelength: 10-500 km
Speed: 600-900 km/hr Fig. 10.36 Coast
Height: 5-30 m, 70 m in
Speed: 35 km/hr Fig. 10.36 Causes of tsunamis: earthquakes Causes of tsunamis: volcanic eruptions Fig. 10.34 Strike-slip faults do NOT produce tsunamis because there is
no vertical offset of seafloor.
Hazards 2: 45 Stromboli, Italy
Hazards 2: 46 Causes: submarine landslides Causes: submarine landslides Fig. 16.9
Hawaii: landslides up to 100 km wide;
debris extends >200 km from source.
Hazards 2: 47 Tsunami deposits at >61-m-elevation
(but may have been at >300 m prior to
Hazards 2: 48 1929: Landslide off coast of
Newfoundland; broke phone
cables; tsunami affected
coast up to 27 m above sea
level Causes: meteorite impact in ocean Tsunamis: extent
Trigger at any
along coast of
to 24+ hours
Atlantic Fig. 23.14a
Hazards 2: 49 65 mya, near Yucatan peninsula, Mexico Tsunamis: warnings
• Warning system in place in Pacific; effectiveness of warning
depends on rapid location of epicenter, magnitude & type of faulting.
• No warning system in place in Indian Ocean prior to 2004 disaster
• No (extensive) warning system yet in Atlantic Ocean 1964 Chile earthquake
Hazards 2: 50 Tsunamis: warnings
** • Tsunamis
• First wave
may not be
largest * • Withdrawal* of
sea… Computer model of
extent of tsunami wave
2 hours and 30 minutes
after earthquake in
Hazards 2: 51 ** *
Hazards 2: 52 Tsunamis in
last 150 years:
Atlantic: Tsunamis: 2004 Indian Ocean Tsunamis: 2004 Indian Ocean Withdrawal of sea… • 9.0 magnitude subduction-zone earthquake
• Fault that slipped was 1100 km long, 100
km wide; produced up to 15 m of slip
• 10-15 m high waves struck Indonesia
minutes after the quake; waves struck
western Africa 6 hours after the quake
• Death toll exceeds 225,000. Fig. 10.38 Fig. 10.35
Hazards 2: 53 Hazards 2: 54 Tsunamis:
2004 Indian Ocean Tsunamis: 2004 Indian Ocean E=epicenter
BA=Banda Aceh, Indonesia (10-15 m high waves)
Contour lines (map, lower left) show location of
first tsunami wave (numbers are hours after EQ). Fig. 10.35 Before tsunami
Hazards 2: 55 Hazards 2: 56 Fig. 10.35 After tsunami Tsunamis: 2004 Indian Ocean
22-17. On December 26, 2004, a magnitude 9 earthquake generated a tsunami that
devastated coastlines along the ____________ Ocean.
22-18. Which plate boundary was responsible for the December 26, 2004, magnitude
A. conservative (transform)
22-19. Which of the following is least likely to cause a tsunami?
A. explosion of a volcanic island B. undersea earthquake on a strike-slip fault
C. undersea landslide
D. meteorite impact in the oceans
22-20. True / B. False: Tsunamis only occur in the Paciﬁc and Indian oceans. Fig. 10.35 Hazards 2: 57 Photo: David Rydevik 22-21. Which statement below is false?
A. The height of a tsunami and the speed of wave motion are both much less in the
open ocean compared to near the shoreline.
B. A tsunami may affect a coastline up to 24 hours after it has been triggered.
C. A tsunami consist of multiple waves, of which the largest may not be the first.
D. The sea-level may lower significantly before the arrival of a tsunami wave.
Hazards 2: 58 ...
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This note was uploaded on 09/25/2011 for the course GEOLOGY 100 taught by Professor Lepre during the Fall '11 term at Rutgers.
- Fall '11