Earthquake facts

1. Earthquake facts • Earthquakes are caused by a build-up of stress within the crust, causing rocks to fail suddenly. • Some 80 percent of all the planet's earthquakes occur along the Pacific rim. • On average, a magnitude 8 (M8) quake strikes somewhere every year. • Most deaths during an earthquake are due to collapsing buildings.

2. Why earthquakes? Where earthquakes?

3. Why earthquakes? Where earthquakes? Distribution of earthquakes with R.S. mag > 5 from 1980-1990.

4. Why earthquakes? Where earthquakes?

5. Honshu tsunami videos http://www.youtube.com/watch?v=w3AdFjklR50&feature=related http://www.youtube.com/watch?v=-DSSssHxm4Y&feature=related http://www.youtube.com/watch?v=s8L2kikyVzk

6. Locating EQs

7. Locating EQs epicenter M=9.0 11 March 2011 5:46:23 UTC focus

8. Faults are where rocks break and move suddenly 30-40 m movement along subduction zone fault in Honshu North American Plate Pacific Plate

9. Tsunami (seismic sea wave) caused by seafloor displacement . Tsunamis slow and steepen (up to 30 m) as they enter shallow water.

10. Tsunami wave predictions

11. Measurement of Earthquakes • Magnitude -an index of the amount of energy released, proportional to amount of ground motion; -Richter Scale - a logarithmic scale: each number represents >30X more energy and 10X more ground motion than preceding number; examples….

12. Richter magnitude depends on: • Separation time (distance) • Amplitude (ground shaking)

13. Measurement of Earthquakes • Intensity -based on damage, effects -will vary from place to place

16. Destructive Effects of Earthquakes • Structural damage from seismic waves- • fire • mass wasting - landslides, liquefaction • tsunami (seismic sea waves)

17. Kobe, Japan, 1995

18. http://environment.nationalgeographic.com/environment/natural-disasters/earthquake-profile.html?fs=video.nationalgeographic.com (National Geographic) http://www.youtube.com/watch?v=SgRry6GZxUo&feature=related(hole in highway) http://www.youtube.com/watch?v=6iNUvlU0SJY (global EQs for 2-month period) http://www.youtube.com/watch?v=reDKxgb_IBQ&feature=related (7.2 quake hits Japan, 2008) http://www.youtube.com/watch?v=7TQDQAesJvM&feature=related (NYC EQ)

20. F =100 lbs 10 lbs/ft2 A =10 ft2 Stress is force concentrated over an area • Types of Stress Plate Tectonics Setting • Confining None • Compressive Convergent • Extensional Divergent • Shear Transform

21. Strainis the response of a material to stress • Elastic • *Rubber ball • *Earthquake • Plastic • *Modeling clay • *Folded rocks • Brittle • *Pencil • *Faults • Type of Strain depends on: • Temperature • Pressure • Material • Time

22. Plastic flow http://www.pirate4x4.com/tech/billavista/PR-BV60/Materials/stress_strain%201.jpg

23. Folding: plastic • response to stress • strain energy used • up in folding • no earthquakes

25. Faulting: brittle response to stress • slow or sudden release of small or large • amounts of energy • may cause earthquakes

26. Elastic Rebound – causes earthquakes

27. Elastic Rebound

28. Stick-slip Faults • Fault zone may have segments characterized by creep • These may altternate with segments which are stuck (snagged) • As elastic strain accumulates, energy is stored; Subsequently released as large earthquake • Creeping segments store little energy (less dangerous)

29. Stick-slip Faults

31. Seismic Waves • body waves- move only through earth’s interior; -p wave: primary (compressional) wave, fastest, first to arrive at seismic station; 2.4 – 3.2 miles / second ~10,000 mph compare to F-15 ~0.5 miles / second -s wave: secondary (shear) wave -1.8 – 2.4 miles / second - cannot be transmitted through liquid (ex molten rock)

32. P WAVE (compressional wave)

33. S WAVE (SHEAR WAVE)

34. Surface Waves • move only along the surface; • - slowest wave type • Rayleigh, Love waves

35. Surface Waves

36. Determining Distance to Point of Energy Release • Example : thunder and lightning, same source 1) light travels 186,000 miles per sec, instantaneous over 1-25 miles 2) sound travels ~ 1,100 ft per sec Ex. Light-sound time interval of 20 sec indicates lightning was ~ 4 miles away

37. Basic principles of a seismograph…

38. Determining EQ Epicenter S-P interval Record (seismogram) of an earthquake; time separation of arrivals based on wave type. S-P interval shown is ~ 5 minutes.

39. Travel-time graph, used to determine distance from seismic station to epicenter.

40. The location of an epicenter on the midoceanic ridge in the South Atlantic Ocean. S-P time intervals are used from 3 seismic stations.

42. MEASUREMENT OF EARTHQUAKES • Magnitude -an index of the amount of energy released, proportional to amount of ground motion; -Richter Scale - a logarithmic scale: each number represents >30X more energy and 10X more ground motion than preceding number; examples….

43. Richter magnitude depends on: • Separation time (distance) • Amplitude (ground shaking)

44. Measurement (cont.) • Intensity - an index of structural damage -based on modified Mercalli Scale I-XII (see Table ); - structural damage depends on: -magnitude and duration of EQ -distance to epicenter -structural design -character of surface materials upon which buildings rest.

45. USGS, 2005

46. San Francisco following the 1906 earthquake; the R.S. magnitude was estimated at 7.8; There were 1,500 deaths.

47. Area in southern Alaska affected by “Good Friday” earthquake of 1964; R.S. magnitude = 9.2, making it the greatest earthquake to strike North America on record (i.e. for ~ the last 2 centuries).

49. Earthquake Prediction • Basis -historical patterns -precursors • Future major and great EQS in California -probability of major quakes (Fig. 15.22) -waiting for the “Big One” (>8 R.S.) • Great quakes in the Midwest….