Earthquake engineering ge cee 479 679 lecture 2 plate tectonics january 24 2008
Download
1 / 45

Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008 - PowerPoint PPT Presentation


  • 64 Views
  • Uploaded on

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.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Earthquake Engineering GE / CEE - 479/679 Lecture 2. Plate Tectonics January 24, 2008' - maxime


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Earthquake engineering ge cee 479 679 lecture 2 plate tectonics january 24 2008

Earthquake EngineeringGE / CEE - 479/679Lecture 2. Plate TectonicsJanuary 24, 2008

John G. Anderson

Professor of Geophysics


Handout today
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.


Source: Geological Society of America web:

http://www.geosociety.org/science/timescale/timescl.htm


Source: Geological Society of America web:

http://www.geosociety.org/science/timescale/timescl.htm


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.

http://www.physics.mcgill.ca/~crawford/PSG/PSG12/204_97_L12.2_earthxn.html



http://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gifhttp://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif


http://www2.ocean.washington.edu/oc540/lec02-1/http://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif


http://www2.ocean.washington.edu/oc540/lec02-1/http://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif


Why believe plate tectonics
Why believe plate tectonics?http://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif

  • 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.


Why believe plate tectonics1
Why believe plate tectonics?http://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif

  • Ocean drilling results.

  • Hot spots

  • Earthquakes

  • Direct measurements


http://www.ngdc.noaa.gov/mgg/fliers/96mgg04.htmlhttp://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif


Direct measurement using the Global Position Systemhttp://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif


Engineering applications
Engineering applicationshttp://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif

  • Context to understand seismicity

  • Quantitative estimate of earthquake rates

  • Seismic gaps


Distance between two points on the Earth’s surfacehttp://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif

Where:

(φ, ψ) = (latitude, longitude) of selected point on plate boundary

(φ1, ψ1) = (latitude, longitude) of pole of relative rotation


uhttp://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif = relative rate of plate motion

a = radius of Earth, 6370 km

Δ = distance from pole of rotation, in degrees

ω = rotation rate of plates about their pole

(a different use of the symbol ω)


Seismic moment
Seismic Momenthttp://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif

  • 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


Application to japan
Application to Japanhttp://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif

  • 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.


Application to japan cont
Application to Japan (cont.)http://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif

  • 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


Moment magnitude
Moment Magnitudehttp://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif

  • MW=(2/3) log M0-10.73

  • This is the preferred magnitude scale in the seismological community.


Application to japan cont1
Application to Japan (cont.)http://topex.ucsd.edu/marine_topo/gif_images/global_topo_small.gif

  • 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.


ad