Earthquakes.

Transcription

1 Earthquakes

2 Elastic rebound

3 Elastic rebound Rocks store energy elastically When stored stress exceeds the strength of the friction on the fault OR the strength of the rock snap. The longer between quakes, the more energy is stored. The deformation can be measured as a way to predict the size of the next quake.

4 Basic Earthquake Terms Focus (Hypocenter): Epicenter:

5 Basic Earthquake Terms Focus (Hypocenter): where the fault ruptures, where the earthquake actually begins. Usually underground Rupture can propagate along the surface size of quake depends on the amount of rupture Epicenter: point on Earth s surface above the focus, where surface waves begin

6 Earthquake waves Body waves: run through interior of Earth P (primary) wave compressional, fast S (secondary) wave transverse, slower Surface waves: ripples at surface of Earth, much slower

7 Finding the epicenter Use difference in travel time between P and S wave to find distance to epicenter Use several stations to triangulate the one place that is the right distance from each station

8 USGS Earthquakes and plates

9 USGS

10 Earthquakes and plates Diverging: small, shallow Subduction zone: small to very large, shallow to deep Suture zone: small to large, shallow to medium depth Transform: small to large, shallow

11 Magnitude v. intensity Magnitude: amount of energy released in the earthquake Moment magnitude - depends on the area of the surface that ruptures and the average displacement Estimated by amplitude of seismogram

12 Dec. 26, 2004, Sumatra

13 What happened to Richter? Richter magnitude estimated energy from amplitude of the seismogram Could not distinguish between very large magnitudes Required use of a specific seismometer

14 Degree of shaking Intensity

15 Intensity

16 Intensity depends on.. Distance from epicenter USGS

17 Geological substrate USGS

18 Loma Prieta, 1989 USGS

19 Hazards Ground motion Liquefaction Landslides Fire Tsunamis

20 Ground motion USGS Pakistan, 2004

21 USGS

22 Liquefaction Water-soaked sediment; during earthquake, sediment sinks USGS

23 Loma Prieta USGS

24 Loma Prieta USGS

25 Niigata, Japan,

26 Landslides Anchorage, wikipedia/commons/a/a5/ AlaskaQuake-Turnagain.jpg

27 Northridge, 1992

28 Fire: San Francisco USGS

29

30 USGS

31 USGS

32 San Francisco Chronicle

33 Tsunami

34 2012/09/Tsunami_comic_book_style.png

35 Hawaii,

36 USGS

37 Dec. 24, 2004 AP

38 Regions of Earthquake hazard USGS

39 US Earthquake areas California

40 US Earthquake Areas California Alaska

41 US Earthquake Areas California Alaska Missouri USGS

42 New Madrid v USGS

43 US Earthquake Areas California Alaska Missouri Hawaii

44 Date Epicenter Location Maximum Intensity Mag No of Deaths Damage S. Hawaii IX Extensive-S. Hawaii Southern Hawaii XII >100 houses destroyed, tsunami Hualalai VIII Extensive-Kona Kona VIII Extensive Hilo N. of Hilo VIII Extensive Hilo, $5.6M Kalapana VIII Extensive Hilo, $4.1 M Kaoiki IX Extensive, Southern Hawaii, >$6M Kalapana VII Southeast Hawaii, almost $1M

45 Damage from 10/15 EQ

46 Earthquake on faults associated with volcanic activity

47 Earthquake Safety With your group, brainstorm what to do BEFORE, DURING or AFTER a quake to increase your chances of surviving comfortably

48 EQ safety and buildings Unsafe structures: Unreinforced masonry (brick)

49 Pakistan, 2005 USGS

50 Loma Prieta, 1989 Watsonville

51 EQ safety and buildings Unsafe structures: Unreinforced masonry (brick) Pre-1954 houses not bolted to foundation

52 Santa Cruz, Loma Prieta,

53 Coalinga,

54 EQ safety and buildings Unsafe structures: Unreinforced masonry (brick) Pre-1954 houses not bolted to foundation Insufficient bracing of cripple wall

55 Cripple wall

56 Bracing the cripple wall

57 Failed cripple walls

58 EQ safety and buildings Unsafe structures: Unreinforced masonry (brick) Pre-1954 houses not bolted to foundation Insufficient bracing of cripple wall Porch failures

59 Watsonville, Loma Prieta USGS

60 EQ safety and buildings Unsafe structures: Unreinforced masonry (brick) Pre-1954 houses not bolted to foundation Insufficient bracing of cripple wall Porch failures Concrete frame structures

61 Northridge, 1992

62 Pakistan, 2005 USGS

63 Northridge,

64 Loma Prieta, 1989 USGS

65 EQ safety and buildings Unsafe structures: Unreinforced masonry (brick) Pre-1954 houses not bolted to foundation Insufficient bracing of cripple wall Porch failures Concrete frame structures Soft-story structures - missing a wall on the first floor

66 Loma Prieta USGS

67 Loma Prieta USGS

68 Loma Prieta USGS

69 Northridge,

70 So what kinds of buildings are safe?

71 So what kinds of buildings are Wood frame safe?

72 So what kinds of buildings are safe? Wood frame Steel frame Shear walls

73 So what kinds of buildings are safe? Wood frame Steel frame Shear walls Cross-braced

74 So what kinds of buildings are safe? Wood frame Steel frame Shear walls Cross-braced Base isolators /08/110946main_earthquake1-215x300.gif

75 Braced steel buildings

76 Prediction Precursors Seismic gaps

77 Ground tilt Precursors

78 Precursors Ground tilt Seismicwave velocities Electrical resistivity

79 Precursors Ground tilt Seismic-wave velocities Electrical resistivity Well water levels Radon

80 Seismic gaps Areas along fault with lower-than-expected frequency of earthquakes. May indicate the fault is locked up and preparing to fail.

81 Loma Prieta gap USGS

82

83 Parkfield experiment Parkfield (near Cholame Valley) had earthquakes about every 22 years for decades, all about M6.

84 Parkfield experiment Parkfield (near Cholame Valley) had earthquakes about every 22 years for decades, all about M6. Earthquake expected 1988

85 Parkfield experiment Parkfield (near Cholame Valley) had earthquakes about every 20 years for decades, all about M6. Earthquake expected 1988 An earthquake finally happened 9/28/2004

86 Parkfield experiment Parkfield (near Cholame Valley) had earthquakes about every 20 years for decades, all about M6. Earthquake expected 1988 An earthquake finally happened 9/28/2004 Using data from quake to examine precursors

87 Public policy and earthquakes Zoning for hazard

88 Public policy and earthquakes Zoning for hazard Alquist-Priolo Act, 1972 Set out earthquake fault zones: 100 cities, 36 counties Prohibited building on active rupture Required identification and retrofit of at-risk buildings