Thailand Training Program in Seismology and Tsunami Warnings, May 2006

1. Theoretical Seismology 1: Sources Thailand Training Program in Seismology and Tsunami Warnings, May 2006

2. 1960’s: WWSSN (World-wide Standardized Network; 100 stations) CHG 1970’s: SRO (Seismic Research Observatory; 1st global digital network) CHTO 1990’S: GDSN (Global Digital Seismograph Network) 2000’s: Disaster Warning Center Brief History of Global Seismology in Thailand

3. What is the cause of earth movement? • Some earth movements are associated with magma • Or with mine bursts and explosions • Most shaking is caused by failure of rocks in the earth

4. Theoretical Seismology 1: Sources • ・ Describe Earth Rupture • Elastic Rebound • Fault Geometry • Double-couple Force • Seismic Moment Tensor • ・ Models of Earthquake Rupture • Rectangular rupture • Circular rupture • Distributed slip models • ・ Earthquake Size • Magnitudes • Seismic Moment • Energy

5. Concepts and Terminology

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

7. 8.5 feet offset in San Andreas fault from 1906 earthquake. Mirin County Elastic Rebound Theory Reid (1910) (Data in 1851-65, 1874-92, 1906) Asperity

8. Four phases Interseismic Preseismic Coseismic Postseismic Elastic Rebound: Loading or deformation cycle

10. Breaking of Brittle Rock • Build-up of stress (strain energy) • Rupture at weakest point • Break along a plane of weakness • Radiation of seismic waves (In contrast to ductile rock, which fails by creep.)

11. What does a critical amount of applied stress do to a rock?

12. What does a critical amount of applied stress do to a rock? smax smin sint

13. Types of faults Normal fault Dip Slip Thrust (Reverse) fault Strike, dip, slip Oblique-slip fault

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

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

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

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

18. 1940 Imperial Valley, California (Ms 7.1)

19. ＋ ー ＋ ー P-wave first motions Auxiliary plane Fault plane This type of faulting is more likely to produce large tsunamis

20. 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

21. Moment tensor: dipoles and couples u(t)i = S Gij(t) mj 9 components Symmetric matrix so 6 independent (LW p.343; AR p.50)

22. Moment Tensor for an Explosion

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

24. NEIC fault plane and moment tensor solutions • 05 05 18.4 0.587 N 98.459 E 34 G 6.4 6.8 A 1.0 20 695 NIAS REGION, INDONESIA. MW 6.7 (GS), 6.7 (HRV). ME 6.6 (GS). Felt (V) at Padang and Sibolga; (III) at Palembang and Pekanbaru, Sumatra. Felt (III) in Malaysia. Felt on Nias and in Singapore. • Broadband Source Parameters (GS): Dep 34 km; Fault plane solution: NP1: Strike=155, Dip=75, Slip=90; NP2: Strike=335, Dip=15, Slip=90; Rupture duration 7.0 sec; Radiated energy 1.6*10**14 Nm. Complex earthquake. A small event is followed by a larger event about 2 seconds later. Depth based on larger event. • Moment Tensor (GS): Dep 38 km; Principal axes (scale 10**19 Nm): (T) Val=1.57, Plg=65, Azm=39; (N) Val=-0.02, Plg=14, Azm=162; (P) Val=-1.55, Plg=20, Azm=257; Best double couple: Mo=1.6*10**19 Nm; NP1: Strike=10, Dip=28, Slip=121; NP2: Strike=156, Dip=66, Slip=74. • Centroid, Moment Tensor (HRV): Centroid origin time 05:05:24.6; Lat 0.42 N; Lon 98.24 E; Dep 39.0 km Bdy; Half-duration 5.6 sec; Principal axes (scale 10**19 Nm): (T) Val=1.49, Plg=66, Azm=61; (N) Val=0.06, Plg=1, Azm=329; (P) Val=-1.55, Plg=24, Azm=238; Best double couple: Mo=1.5*10**19 Nm; NP1: Strike=326, Dip=22, Slip=88; NP2: Strike=149, Dip=69, Slip=91. Scalar Moment (PPT): Mo=1.3*10**19 Nm.

25. Kinematics

26. Haskell Line Source Haskell, 1964 Specifies Fault length L Fault width W Rupture velocity v Permanent slip D Rise time T

27. Circular Crack – Sato and Hirasawa, 1973

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

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

30. Magnitude is a number that represents earthquake size no matter where you are located. It should be related to released seismic energy. It should handle the smallest earthquake to the largest earthquake. What is magnitude? Why do we need it?

31. January 26, 2001 Gujarat, India Earthquake (Mw7.7) Body waves vertical Rayleigh Waves P PP S SS radial transverse Love Waves Recorded in Japan at a distance of 57o (6300 km)

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

33. 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 short-period P waves ~ 1 sec Ms Surface wave magnitude long-period surface ~ 20 sec waves Mw Moment magnitude very long-period > 145 sec surface waves Me Energy magnitude broadband P waves 0.5-20 sec Mwp P-wave moment magnitude long-period P waves 10-60 sec Mm Mantle magnitude very-long period > 200 sec surface waves

34. Distance range ML(local, Wood Anderson, 0.8 s) Teleseisms (recorded at long distances) mB (uses Amax /T, but in practice T is short-period) MS (uses Amax /T, but in practice T is long-period) Depth MS not useful mb still works, as well as Me and Mw Physical significance More recent magnitudes (Mw and Me) are related to different aspects of earthquake size. Why are there different magnitudes?

35. Quick and simple measurements Usually from band-limited data. single frequency may not all frequencies Saturation single measurement may not represent large rupture ML and mb ~ 6.5 MS ~ 8.5 Empirical formulas Physical significance not certain e.g., from Gutenberg-Richter, log ES = 11.8 + 1.5 MS What are the limits of historic magnitudes(ML ,mb, and Ms)?

36. More Recent Magnitude Scales Mw Moment magnitude very long-period surface waves > 145 sec Me Energy magnitude broadband P waves ~ 0.5-20 sec Mwp P-wave moment magnitude long-period P waves 10-60 sec Mm Mantle magnitude very-long period surface waves > 200 sec

37. MW is derived from - Seismic Moment Mw = 2/3 log M0 - 6.0 Area (A) Slip (S) Seismic Moment = (Rigidity)(Area)(Slip)

38. 2004 Sumatra 400 x 1027 dyne-cm Mw 9.3 Seismic moments and fault areas of some famous earthquakes

39. Mw is derived from moment, which is sensitive to displacement Me is computed from energy, which is sensitive to velocity Mw compared to Me Different magnitudes are required to describe moment and energy because they describe different characteristics of the earthquake.

40. These two earthquakes in Chile had the same Mw but different Me

41. Earthquakes with the same Mw can have different macroseismic effects. For the Central Chile earthquakes: Earthquake 1: 6 July 1997 30.0 S 71. W Me 6.1, Mw 6.9 Felt (III) at Coquimbo, La Serena, Ovalle and Vicuna. Earthquake 2: 15 October 1997 30.9 S 71.2 W Me 7.6 Mw 7.1 Five people killed at Pueblo Nuevo, one person killed at Coquimbo, one person killed at La Chimba and another died of a heart attack at Punitaqui. More than 300 people injured, 5,000 houses destroyed, 5,700 houses severely damaged, another 10,000 houses slightly damaged, numerous power and telephone outages, landslides and rockslides in the epicentral region. Some damage (VII) at La Serena and (VI) at Ovalle. Felt (VI) at Alto del Carmen and Illapel; (V) at Copiapo, Huasco, San Antonio, Santiago and Vallenar; (IV) at Caldera, Chanaral, Rancagua and Tierra Amarilla; (III) at Talca; (II) at Concepcion and Taltal. Felt as far south as Valdivia. Felt (V) in Mendoza and San Juan Provinces, Argentina. Felt in Buenos Aires, Catamarca, Cordoba, Distrito Federal and La Rioja Provinces, Argentina. Also felt in parts of Bolivia and Peru.

42. 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

43. 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

44. Mwp P-wave moment magnitude ∫uz(t)dt ∝ Mo ・ Quick magnitude from P wave ・ Uses relatively long-period body waves (10-60 sec) ・ Some problems for M>8.0

45. Magnitudes for the Sumatra Earthquake mb 7.0 1 sec P wave 131 stations Mwp 8.0 – 8.5 60 sec P waves Me 8.5 broadband 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

46. 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 earthquake can be described by different magnitudes, by moment, and by energy. 5. Quick determination of magnitude is needed for tsunami warning systems.

48. Relationship between different types of magnitudes

49. 15 km M4 M5 M6 10 5 0 M4 M5 M6 Seismicity in NEIC catalog 1990 - 2005

50. Log E = 1.5Ms + 4,8 Log E = 1.5 Me + 4.4