22_hazards2_09_post - 22: Natural Hazards 2 Earthquakes...

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Unformatted text preview: 22: Natural Hazards 2 Earthquakes & Tsunamis Earthquakes: largest Mexico City, 1985 Kobe, Japan, 1995 Indian Ocean tsunami, 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 collapses Hazards 2: 7 (f) Concrete-block, brick or adobe buildings crack apart and collapse (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 See Fig. 10.32 Liquefaction increases risk of landslides. Liquefied sediment expelled from fissure following 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 ___. A. 9.5 B. 9.2 C. 9.1 D. 9.0 22-2. A. True / B. False: The earthquake with the highest death toll also had the highest magnitude. 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. D. Tsunamis. 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 population centers 4. Style & quality of construction Fig. 10.30b See Table 10.2 Taiwan, 1990 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) form during 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 recurrence interval? A. 150 yrs B. 200 yrs C. 250 yrs 250 yr 200 yr 450 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 450 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: earthquake progression… from east to west Gap Stress trigger? Hazards 2: 35 • Foreshocks: small earthquakes that precede a larger earthquake, most likely related to cracking of stressed rocks. • Change in water levels of wells, animal behavior, 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 is better 2. Install auto-gas shutoffs; know location of gas & electric shutoffs 3. Fasten (book)cases to walls 4. Avoid building on slopes, unconsolidated materials 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. A. Conservative B. Convergent C. Divergent 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 recurrence interval. 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 unconsolidated sediments. 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 narrow bays 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 Fig. 16.10 Hawaii: landslides up to 100 km wide; debris extends >200 km from source. Oregon continental margin Hazards 2: 47 Tsunami deposits at >61-m-elevation (but may have been at >300 m prior to subsidence) 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 location in ocean may cause tsunami anywhere along coast of that ocean from minutes to 24+ hours after event Number of tsunamis: Pacific>Indian> 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 consist of multiple waves • First wave may not be largest * • Withdrawal* of sea… Computer model of extent of tsunami wave 2 hours and 30 minutes after earthquake in Aleutian Islands Hazards 2: 51 ** * Fig. 10.37 Hazards 2: 52 Tsunamis in last 150 years: Caribbean: 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 Review Questions 22-17. On December 26, 2004, a magnitude 9 earthquake generated a tsunami that devastated coastlines along the ____________ Ocean. A. Atlantic B. Arctic C. Indian D. Pacific 22-18. Which plate boundary was responsible for the December 26, 2004, magnitude 9 earthquake? A. conservative (transform) B. convergent C. divergent 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.

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