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Tsunami: Building up Stress and the Breaking of Chopsticks

Learn about the breaking of chopsticks as a metaphor for the build-up of stress and how tsunamis occur due to sudden changes in underwater topography like earthquakes, volcanic eruptions, and landslides.

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Tsunami: Building up Stress and the Breaking of Chopsticks

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  1. Breaking of Chopstick ・ Failure ・ Build-up of stress (strain energy) ・ Difficult to predict time and place ・ Breaks at weakest point ・ Hear precursors ・ Sound of breaking same as seismic waves

  2. Sources of Tsunami Sudden submarine topographic change ・Crustal deformation by earthquake. ・Submarine volcanic eruption. 　・Landslide near coastline or submarine landslide.

  3. Tsunami by Volcanic Eruption Eruption of Krakatau in Aug. 1883. Krakatau More than 36,000 people were killed. Ref. http://www.geology.sdsu.edu/how_volcanoes_work/Krakatau.html

  4. Tsunami by Landslide Landslide Tsunami The landslide was triggered by an earthquake on May 21, 1792. More than 15,000 people were killed mainly by tsunami.

  5. Tsunami by Earthquake

  6. 6. Introduction of Simulation Technique(since 1999) Occurrence of Earthquake Detection of Seismic Wave Empirical method a) Distance to epicenter b) Magnitude of earthquake Strong motion seismograph Short-period seismograph Quantitative method Simulation of tsunami Dedicated telephone network Determination of Source Parameters Automatic Processing System Mp ・・・・ 18 66 Evaluation of Tsunami <Tsunami Forecast Regions> 18 　　　 →　 66 <Contents of Tsunami Forecast> 1. Generation of Tsunami 1. Generation of Tsunami 2. Tsunami Grade → 2. Tsunami Grade 3. Expected arrival time 3. Expected arrival time 4. Expected tsunami height Quantitative Tsunami Forecast Issuance of Tsunami Warning average issuance time 3 to 5 min

  7. Theoretical Seismology 1: Sources ・ What is the Earthquake Source? Elastic Rebound Fault Slip Double-couple Force ・ Seismic Moment Tensor ・ Models of Earthquake Faults ・ Earthquake Size Magnitudes Seismic Moment Energy

  8. What is the cause of Earthquakes ? • ・ Associated with faults • (source or cause?) • ・ Associated with magma? (Most) Earthquakes are fault movements

  9. Types of faults Normal fault Thrust (Reverse) fault Strike-slip fault

  10. Strike-Slip Faults Left-lateral Right-lateral

  11. 1940 Imperial Valley, California (Ms 7.1)

  12. San Francisco Earthquake April 18, 1906 Mw 7.7-7.9 470 km rupture of San Andreas fault

  13. S phase Reading arrival time of P phase & S phase Determination of Hypocenter P phase 15.3mm 19:23:04.78 19:23:07.53 Maximum amplitude Hypocenter (Distance) Determination of magnitude Reading Maximum Amplitude Seismogram Japan Meteorological Agency 2005/3/9

  14. ＋ ー ＋ ー P-wave first motions This type more likely to produce large tsunamis

  15. Harvard/NEIC Moment Tensor Solutions

  16. Haskell Line Source Dislocation Source Haskell, 1964 sumatra Sumatra earthquake Ishii et al., 2005

  17. Complicated Slip Distributions - 1999 Chi-Chi, Taiwan Earthquake

  18. Single-force earthquakesvolcanic eruptions and landslides Mount St. Helens, USA Kanamori et al. 1984

  19. Earthquake Size – Magnitude Charles Richter 1900-1985 log of amplitude Distance correction M = log A – log A0 Richter, 1958

  20. Magnitude Determination Magnitude, Size of Earthquake (Defined by Richter (1935) at first) M=log10(Amplitude)+(Correction for Distance) Amplitude×0.1 ⇒ M－１ Amplitude×10 ⇒ M＋１ Amplitude×100 ⇒ M＋２

  21. Types of Magnitude Scales Period Range ML Local magnitude (California) regional S and 0.1-1 sec surface waves Mj JMA (Japan Meteorol. Agency) regional S and 5-10 sec surface waves mb Body wave magnitude teleseismic P waves 1-5 sec Ms Surface wave magnitude teleseismic surface 20 sec waves Mw Moment magnitude teleseismic surface > 200 sec waves Mwp P-wave moment magnitude teleseismic P waves 10-60 sec Mm Mantle magnitude teleseismic surface > 200 sec waves

  22. Magnitudes for the Sumatra Earthquake mb 7.0 1 sec P wave 131 stations mblg 6.7 1 sec Lg waves 6 stations Mwp 8.0 – 8.5 60 sec P waves Ms 8.5 - 8.8 20 sec surface waves 118 stations Mw 8.9 - 9.0 300 sec surface waves Mw 9.1 - 9.3 3000 sec free oscillations

  23. Relationship between different types of magnitudes

  24. Earthquake size - Seismic Moment Area (A) Slip (S) Seismic Moment = (Rigidity)(Area)(Slip)

  25. Mwp P-wave moment magnitude Mo = Max |∫uz(t)dt| 4pra3r/Fp Mw = (log10Mo – 9.1)/1.5 ・ Quick magnitude from P wave ・ Uses relatively long-period body waves (10-60 sec) ・ Some problems for M>8.0

  26. Mwp P-wave moment magnitude ∫uz(t)dt ∝ Mo

  27. 2004 Sumatra 400 x 1027 dyne-cm Mw 9.3 Seismic moments and fault areas of some famous earthquakes

  28. Ground Displacement Length Earthquake Magnitude and Tsunami M:+1→Displacement×3, Length×3 Richter Scale = Magnitude

  29. Magnitude and Tsunami Water volume lifted by the fault motion ≒(Area)×(Displacement) Magnitude +1 ×３（Fault Length）×３（Fault Width）×３（Displacement） ≒30 times Magnitude +2 ×10（Fault Length）×10（Fault Width）×10（Displacement） ≒1000 times

  30. Rupture Propagation Rupture Velocity < S-wave Speed Duration of Rupture = Fault Length÷Rupture Velocity Magnitude　～ 7 Duration = (50km)÷(3km/s) =10and several (sec) Magnitude　～ 8 Duration = (100～150ｋｍ)÷（3km/s） =30 (sec)～1(min) Earthquake on Dec. 26 2004 Rupture Velocity ≦ 2km/s Duration > 10 min

  31. Magnitudes for Tsunami Warnings ・ Want to know the moment (fault area and size) but takes a long time (hours) to collect surface wave or free oscillation data ・ Magnitude fromP waves (mb) is fast but underestimates moment 　　⇒　If have time (hours), determine Mm from mantle waves ⇒ For quick magnitude (seconds to minutes), determine Mwp from P waves

  32. Things to Remember 1. Earthquake sources are a double couple force system which is equivalent to Fault Slip 2. The moment tensor describes the Force System for earthquakes and can be used to determine the geometry of the faulting 3. Earthquake ruptures begin from a point (hypocenter) and spread out over the fault plane 4. The size of an earthquakes can be described by magnitudes, moment, and energy. Mm and Mwp are types of magnitudes used for tsunami warning systems

  33. Tsunami Magnitude Distant tsunami (Δ> 1000 km) Mt=log10H+C+9.1 C, Correction constant. Local tsunami Mt=log10H+log10Δ+5.80 H, Tsunami height (m). Δ, Epicentral distance (km), 100 km ≦Δ≦ 3,500 km. (Abe, 1979, 1981) (Used to express size of tsunami effect.)

  34. Thank you for your attention

  35. Chang Heng ‘Seismometer’ AD132 Giuseppe Mercalli (1850-1914) John Milne (1850-1913) Sassa Seismometer (~1935), Abuyama, Kyoto Univ.

  36. What is an Earthquake ? The Source Fault mechanisms The Shaking Wave propagation Structures

  37. Elastic Rebound Theory Reid (1910) 8.5 feet offset in San Andreas fault from 1906 earthquake. Mirin County (Data in 1851-65, 1874-92, 1906)

  38. Controversy settled by Maruyama (1963) Showed that Double Couple was equivalent to fault slip Single Couple versus Double Couple Single Couple Double Couple • ・ P polarity pattern same • ・ S polarity pattern different • ・ Single Couple ‘resembles’ fault slip

  39. Equivalent Body Forces Single Force Dipole Couple (Single Couple) Double Couple

  40. Moment tensor: dipoles and couples 9 components Symmetric matrix so 6 independent (LW p.343; AR p.50)

  41. Moment Tensor for an Explosion

  42. Moment Tensor for Fault Slip North ⇒ Double Couple Fault - Slip

  43. Circular Crack – Sato and Hirasawa, 1973

  44. Mm Mantle Magnitude Source Correction Mm = log10(X(w)) + Cd + Cs – 3.9 Distance Correction Spectral Amplitude ・ amplitude measured in frequency domain ・ surface waves with periods > 200 sec

  45. Fault Areas of Damaging Earthquakes 1995 Kobe Mw 6.9 Deaths 1944 1223 1946 1330 1995 6310 1944 Tonankai Mw 8.1 1946 Nankai Mw 8.1

  46. 15 km M4 M5 M6 10 5 0 M4 M5 M6 Seismicity in NEIC catalog 1990 - 2005

  47. 2004 Sumatra 400 x 1027 dyne-cm Mw 9.3 Fault areas of some famous earthquakes

  48. Seismic Radiated Energy Radiated Energy = 1.5Mw + 11.8 Kanamori, 1977

  49. Types of Magnitude Scales Period Range ML Local magnitude (California) regional S and 0.1-1 sec surface waves Mj JMA (Japan Meteorol. Agency) regional S and 5-10 sec surface waves mb Body wave magnitude teleseismic P waves 1-5 sec Ms Surface wave magnitude teleseismic surface 20 sec waves Mw Moment magnitude teleseismic surface > 200 sec waves Mwp P-wave moment magnitude teleseismic P waves 10-60 sec Mm Mantle magnitude teleseismic surface > 200 sec waves

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