earthquake engineering ge / cee - 479/679 lecture 2. plate tectonics january 24, 2008
DESCRIPTION
Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008. John G. Anderson Professor of Geophysics. Handout Today. Chapter 2. Plate Tectonics Students are advised to read this as your textbook on this topic. Solve exercises 3, 4, 5, 6, and 8. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/1.jpg)
January 24, 20081
Earthquake EngineeringGE / CEE - 479/679
Lecture 2. Plate TectonicsJanuary 24, 2008
John G. Anderson
Professor of Geophysics
![Page 2: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/2.jpg)
January 24, 20082
Handout Today
• Chapter 2. Plate Tectonics– Students are advised to read this as your
textbook on this topic.– Solve exercises 3, 4, 5, 6, and 8.– For extra credit, solve exercises 9, 11.– Exercises are due Jan. 31.
![Page 3: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/3.jpg)
Source: Geological Society of America web: http://www.geosociety.org/science/timescale/timescl.htm
![Page 4: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/4.jpg)
Source: Geological Society of America web: http://www.geosociety.org/science/timescale/timescl.htm
![Page 5: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/5.jpg)
January 24, 20085
http://www.physics.mcgill.ca/~crawford/PSG/PSG12/204_97_L12.2_earthxn.html
Crust - rocks (granite, basalt); density ~ 3 g/cm3
Lithosphere - "rock-sphere" - rigid layer (includes crust)
Asthenosphere - "weak-sphere" (lower v seismic waves) Convection currents flow in the 'plastic' asthenosphere, and the plates of the lithosphere ride on these.
Mantle - iron-rich, mainly solid rock
Outer core - liquid iron and nickel
Inner core - solid iron, nickel
Distances are in kilometers.
![Page 6: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/6.jpg)
January 24, 20086
The radii for the tops of the major layers are more accurate on this plot.
![Page 7: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/7.jpg)
January 24, 20087
![Page 8: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/8.jpg)
![Page 9: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/9.jpg)
January 24, 20089
http://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif
![Page 10: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/10.jpg)
January 24, 200810
http://www2.ocean.washington.edu/oc540/lec02-1/
![Page 11: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/11.jpg)
January 24, 200811
http://www2.ocean.washington.edu/oc540/lec02-1/
![Page 12: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/12.jpg)
January 24, 200812
Why believe plate tectonics?
• Geography - matching continental boundaries.• Geology - units match where continental
boundaries match.• Paleomagnetism
– Characteristics of the magnetic field
– Polar wander
– Mid-ocean ridge magnetic anomalies.
– Past and future Earth.
![Page 13: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/13.jpg)
January 24, 200813
Why believe plate tectonics?
• Ocean drilling results.
• Hot spots
• Earthquakes
• Direct measurements
![Page 14: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/14.jpg)
January 24, 200814
![Page 15: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/15.jpg)
January 24, 200815
![Page 16: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/16.jpg)
January 24, 200816
![Page 17: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/17.jpg)
January 24, 200817
![Page 18: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/18.jpg)
![Page 19: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/19.jpg)
January 24, 200819
![Page 20: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/20.jpg)
![Page 21: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/21.jpg)
![Page 22: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/22.jpg)
January 24, 200822
![Page 23: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/23.jpg)
![Page 24: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/24.jpg)
January 24, 200824
![Page 25: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/25.jpg)
January 24, 200825
![Page 26: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/26.jpg)
http://www.ngdc.noaa.gov/mgg/fliers/96mgg04.html
![Page 27: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/27.jpg)
![Page 28: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/28.jpg)
January 24, 200828
![Page 29: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/29.jpg)
![Page 30: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/30.jpg)
January 24, 200830
![Page 31: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/31.jpg)
January 24, 200831
Direct measurement using the Global Position System
![Page 32: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/32.jpg)
![Page 33: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/33.jpg)
![Page 34: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/34.jpg)
January 24, 200834
Engineering applications
• Context to understand seismicity
• Quantitative estimate of earthquake rates
• Seismic gaps
![Page 35: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/35.jpg)
January 24, 200835
cos sin sin cos cos cos( )Δ = + −φ φ φ φ ψ ψ1 1 1
Distance between two points on the Earth’s surface
Where:(φ, ψ) = (latitude, longitude) of selected point on plate boundary(φ1, ψ1) = (latitude, longitude) of pole of relative rotation
![Page 36: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/36.jpg)
January 24, 200836
![Page 37: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/37.jpg)
![Page 38: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/38.jpg)
January 24, 200838
u a=ω sinΔu = relative rate of plate motiona = radius of Earth, 6370 kmΔ = distance from pole of rotation, in degreesω = rotation rate of plates about their pole
(a different use of the symbol ω)
![Page 39: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/39.jpg)
January 24, 200839
( ) ( )okm
cmkm
y
myradians
myu 77sin10637010
deg180
deg98.0 56
⎭⎬⎫
⎩⎨⎧
⎟⎠
⎞⎜⎝
⎛
⎭⎬⎫
⎩⎨⎧
⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛= −π
![Page 40: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/40.jpg)
![Page 41: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/41.jpg)
January 24, 200841
Seismic Moment
• Definition of Seismic Moment
• M0=μAD
– μ is the shear modulus of the rock– A is the area of the fault on which slip takes
place– D is the average slip on the fault
![Page 42: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/42.jpg)
January 24, 200842
Application to Japan
• Accept for the time that the plates in Japan converge at u=10.6 cm/yr.– This is a horizontal convergence rate.– .
• The last large earthquake at Tokyo was 1923. – Time past is (2005-1923)=84 years.
• Then accumulated slip is: – 10.6 cm/yr*82 yr=890 cm.
![Page 43: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/43.jpg)
January 24, 200843
Application to Japan (cont.)
• Then accumulated slip is: – 10.6 cm/yr*82 yr=890 cm.
• Suppose the fault is 200 km long and the seismogenic zone is from 0 to 30 km depth.– The subduction zone dips, lets say at 40o
– Width = 30 km/cos(dip)=40 km• M0=μAD
= 4*1011 dyne/cm2 * 200 km * 40 km * (105 cm/km)2 * 890 cm
= 2.8 * 1028 dyne-cm
![Page 44: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/44.jpg)
January 24, 200844
Moment Magnitude
• MW=(2/3) log M0-10.73
• This is the preferred magnitude scale in the seismological community.
![Page 45: Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008](https://reader036.vdocuments.mx/reader036/viewer/2022062315/568158f9550346895dc63415/html5/thumbnails/45.jpg)
January 24, 200845
Application to Japan (cont.)
• M0=μAD=2.8 * 1028 dyne-cm
MW=(2/3) log M0-10.73 =8.24
Conclusion, by these assumptions, there is enough strain accumulated to cause a MW=8.2 earthquake under Tokyo.