1. GEOG 3251: Mountain Geog, summer 2007 Adina Racoviteanu

2. Objectives Relate earthquake activity to plate tectonics Define earthquake, focus and epicenter Describe the types of waves emitted during an earthquake. Distinguish between earthquake intensity and magnitude. VIDEO: Methods of earthquake prediction.

3. What is an earthquake? Earthquake = Vibration of the Earth produced by the rapid release of energy Seismic waves = Energy moving outward from the focus of an earthquake

4. Why do earthquakes occur? Fractures, faults Energy released and propagates in all directions as seismic waves causing earthquakes Focus = location of initial slip on the fault; where the earthquake originates Epicenter = spot on Earth’s surface directly above the focus

5. Where do earthquakes occur? 1) Most earthquakes (90%) occur along the edge of oceanic and continental plates 2) Some along faults: normal, reverse, transform

6. Seismic waves: forms P-waves: –compressional, or push-pull waves –Propagate parralel to the direction in which the wave is moving –Move through solids, liquids S-waves: –Called shear waves –Propagate the movement perpendicular to the direction in which the wave is moving Surface waves (L-waves or long waves). –Complex motion –Up-and-down and side-to-side –Slowest –Most damage to structures, buildings

7. Seismic waves: properties Velocity: function of the physical properties of the rock the wave is traveling through –Velocity changes when passing from one material to another (increases/decreases) –Liquids: S-waves do not get transmitted through liquid P-waves slow down Why is this important? –If we know the velocity of the wave, we can infer the type of rock it traveled through- that’s how we map the interior of the Earth!!!

8. Measuring earthquakes Seismometers: instruments that detect seismic waves Seismographs Record intensity, height and amplitude of seismic waves

9. Locating the shaking

10. Earthquake size: two ways to measure 1)Magnitude: Richter Scale 2)Intensity: Mercalli Scale

11. 1) Richter Scale Measures the energy released by fault movement related to the maximum amplitude of the S wave measured from the seismogram Logarithmic-scale 5 6 31.5 times energy 7 992 times more energy !!

12. 2) Intensity: Mercalli Scale: –What did you feel? –Assigns an intensity or rating to measure an earthquake at a particular location (qualitative) –I (not felt) to XII (buildings nearly destroyed) –Measures the destructive effect Intensity is a function of: Energy released by fault Geology of the location Surface substrate: can magnify shock waves e.g. Mexico City (1985) and San Francisco (1989)

13. Frequency of Occurrence of Earthquakes DescriptorMagnitudeAverage Annually Great8 and higher1 ¹ Major7 - 7.917 ² Strong6 - 6.9134 ² Moderate5 - 5.91319 ² Light4 - 4.9 13,000 (estimated) Minor3 - 3.9 130,000 (estimated) Very Minor2 - 2.9 1,300,000 (estimated) ¹ Based on observations since 1900. ² Based on observations since 1990.

14. Recent Earthquake Activity around the World

15. Largest earthquakes in the world since 1900

16. Largest earthquake in the world Chile : May 22, 1960 Magnitude 9.5 More than 2,000 killed, 3,000 injured, 2,000,000 homeless, and $550 million damage in southern Chile tsunami caused 61 deaths $75 million damage in Hawaii; 138 deaths and $50 million damage in Japan; 32 dead and missing in the Philippines; and $500,000 damage to the west coast of the United States.

18. Most Destructive Known Earthquakes on Record in the World DateLocationDeathsMagnitudeComments May 31, 1970Peru66,0007.9$530,000,000 damage, great rock slide, floods. July 27, 1976China, Tangshan 255,000 (official) 7.5Estimated death toll as high as 655,000. Sept 19, 1985Mexico Michoacan 9500 (official) 8.0 Estimated death toll as high as 30,000 Old lake bed magnified shock waves by 500% 2001 Jan 26India20,0237.7166,836 injured, 600,000 homeless. 2004 Dec 26Sumatra283,1069.0Deaths from earthquake and tsunami

19. What Controls the Level of Shaking? Magnitude –More energy released Distance –Shaking decays with distance Local soils –amplify the shaking

20. Ground shaking Kobe, Japan 1995

21. Surface faulting Landers, CA 1992

22. Landslides Source: National Geophysical Data Center Turnnagin Heights,Alaska,1964

23. Fires Loma Prieta, CA 1989

24. India, Gujarat earthquake Jan 26, 2001

25. Later that year… Arequipa. S.Peru June 2001

26. Jun 23, 2001 Magnitude 8.1 earthquake strikes Arequipa

27. Earthquake damage Ground Failure - constructions collapse Fires - from broken gas and electrical lines Landslides - EQ's triggered; occur in hilly/mountainous areas. Liquefaction - water-saturated, unconsolidated materials flow Tsunami (seismic sea waves; "tidal" waves) - can grow up to 65 m

28. Natural disasters in the Cordillera Blanca, Peru: Huascaran avalanche

29. Favoring conditions Major tectonic faults that are active Marked glacierization Geologically young, steep mountains Pro-glacial lakes Immediate vicinity of human settlements

30. Mass wasting: types Creep Landslides: rock slides Flows: avalanches, debris flow, mud flow Falls

32. Alaska

33. Lahars= debris flows associated with volcanic eruptions

34. Landslide and Debris Flow (Mudslides): masses of rock, earth, or debris saturated with water and moving down a slope They are activated by:  storms,  earthquakes,  volcanic eruptions,  fires,  alternate freezing or thawing,  steepening of slopes by erosion or human modification.

35. Avalanche: –similar in mechanism to landslide –it involves a large amount of ice, snow and rock falling quickly down the side of a mountain –ice builds in cornices or forms over a weaker layer of snow, creating the danger of an avalanche.

37. ALPAMAYO Nev. Chacraraju

38. Artesonraju

39. HUANDOY

40. Mt. HUASCARAN, PERU

41. 1962 HUASCARAN AVY Large snow year 50 degree F increase in temp over a few minutes Caused avalanche 4,000 fatalities

42. 1970 Avalanche Triggered by 7.7 magnitude earthquake Rock face failure Incorporated 30 meters of snow and ice! Moraines confined flow initially Accelerated over a distance of 2.4 km Became airborne at change of slope

44. Landslides: May 30, 1970 Peru disaster Magnitude: 7.9 A large mass of ice and rock slid from a vertical face on Nevado Huascaran, the highest peak in Peru Debris reached a velocity of 280 km/hr traveled 11 km horizontally in about 4 minutes at a mean velocity of 165 km/hr. Buried the towns of Yungay and Ranrahirca, The death toll in both villages was 20,000.

45. 1970 Earthquake that caused the Huascaran disaster killed about 40,000 people in Huaraz. Streets of Huaraz after the 1970 Earthquake. Adobe houses collapsed, killing people inside.

46. The town of Huaraz flattened

47. Huaraz today: a growing tourist town

53. Church before 1970 avalanche. Note palm trees in foreground.

54. Many years after the avalanche. Note palm trees survived.

55. Yungay is now completely abandoned. Cemetery has a monument to the dead.

57. Summary 1962 Huascaran avalanche killed 4,000 1970 Huascaran avalanche killed 20,000 earthquake triggered avalanches

58. Earthquake risk and prediction Long-term methods 1) seismic hazard maps 2) probability analysis based on: - historical EQ records - geologic EQ records - slip-rate on active faults - frequency and magnitude of recent EQ's Real-time 24 Hour Forecast

59. Short-term predictions Precursor phenomena (<1 year to days) 1. Foreshocks: usually increase in magnitude 2. Ground deformation 3. Fluctuations in water well levels 4. Changes in local radio wave characteristics 5. Anomalous animal behavior???