1. Earthquakes

2. If the Earth’s a rockin’…. Deformation –Elastic deformation (rubber band)—object being deformed stretches building up potential energy Remove stress  energy released  object returns to normal –Everything has limits Stretching a rubber band until it breaks –Rocks behave similarly

3. The Stress Builds

4. Where do earthquakes occur Tend to form along plate boundaries Earth’s surface is divided into ~16 plates Plates interact by ramming into and sliding past each other

5. Earthquake Strength Old system—Mercalli scale –Based on building damage –inaccurate Richter Scale (M L ) –Magnitude 5.0 has amplitude 10x that of 4.0 –Based on height of largest peak on seismograph –Richter less accurate above M L =6.5 Moment Magnitude (M w ) –Total energy expended during quake –Measured from fault offset, area affected –Each increment is 30 times stronger than the one previous to it

6. Richter Scale Practical equivelents avg. San Andreas quakes Sumatran Tsunami quake

7. Earthquakes…globally

8. Transform Boundary EQs Transform margin –Plates grind past each other—strike-slip fault –One large fault— numerous smaller ones San Andreas Fault Zone –10,000 Eqs/year –Periodic large quakes

9. Great San Francisco Quake of 1909 Mw 7.8 City of San Fran completely destroyed Fires caused by ruptured gas mains caused 99% of the damage—rebuilding costs comparable to Hurricane Katrina 3000 people died

10. Strike-slip motion 3 ways that the NAM plate slides past the Pac plate –Fault creep—smooth –Hopping—movement occurs as a series of jumps—series of small Eqs –Catastrophic breaks— fault sticks and releases generating one big Eq

11. Convergent Plate Eqs Benioff zone—area along top of subducting plate frequented by Eqs Tend to be large and devastating –Coastal population threat Tsunamis often generated –“harbor wave” –Huge waves caused by displacement of water

12. Sumatra Tsunami 7:59 AM, Dec. 26, 2004 M w =9.0 Subduction Zone –Indian + Burma Plate –15 m total movement, seafloor rises sev. m –700 kph (420 mph) –Total deaths: 283,000 (~2.5x pop of McKinney)

13. Why There? Why So Big? Indian moving NE at 6 cm/yr Plate was stuck –For likely 100s of years –Burma Plate bends Burma Plate Indo-Australian Plate

14. Burma Plate flexes/moves 1200 km length of subduction zone displaced vertically 15 m Causes sea level to rise/fall Big wave generated

15. Tsunami Like an Ocean Wave A particle on the surface moves in a circular fashion –Effects of waves disappear at about ½ wavelength –Tsunami wavelength ~ 180 km (much deeper than oceans) –Tsunami drags on ocean floor

17. Sumatra Tsunami, 2004 Waves were ~10m (32’) and 24m locally In Sumatra and Thailand – people live on coast –Homes are usually less than 15’ –Energy carries waves inland, maybe 1-8 km –And then wave goes back out –Time between waves can be >30 minutes –The benefit of a good education

18. VideoVideo 1

19. Notice: bent waves

20. Damage Control People outside are safer (even in tsunami)People outside are safer (even in tsunami) Biggest danger is overheadBiggest danger is overhead –Neighboring buildings –Unsupported buildings, glass, and just about anything not nailed down If caught inside:If caught inside: –Lie down next to something that won’t flatten (not in doorways or under table)

21. Politics and Predictions Hysteria vs. withholding information Predictions and chance The need for short-term predictionsThe need for short-term predictions Uncertainty!Uncertainty! Tangshan 1976 242,769 deaths No warning

22. Problems and Precursors Large earthquakes and changing stress –Large earthquakes can put stress on neighboring faults Foreshocks Radon Gas?? –Fracturing of rock allows radon gas to seep into foundations Earthquake frequency changes, clustering

23. Long-Term Forecasts If you knew decades in advance: –Construction projects, insurance More reliable than short-term predictions Recurrence interval of past events Risk Maps