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THESIS, Munich, 13.06.2006

This thesis conducted a study on ground motion variation by utilizing the Numerical Green’s Function method. The research focused on the uncertainty caused by hypocenter location and varying slip distribution. The findings confirmed the influence of horizontal hypocenter location and directivity effect on ground motion. Future work includes investigating rotational motions and exploring the source vs. 3D effects for rotations.

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THESIS, Munich, 13.06.2006

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  1. THESIS, Munich, 13.06.2006 Using Numerical Green’s Function Method to Investigate Ground Motion Variation Haijiang Wang LMU In collaboration with Heiner Igel, LMU, Alain Cochard, LMU, Michael Ewald, LMU.

  2. Outline • Motivation (source related ground motion uncertainty) • Numerical Green‘s Function approach • Uncertainty – due to hypocentre location • Uncertainty – due to varying slip distribution • Conclusions

  3. Motivation Amplitude amplification Duration time elongation Ewald et al., 2006 Basin effect But few attention was paid on source complexity (3D) ...

  4. Motivation For large earthquake, point source is not sufficient and at least kinematic finite source is necessary to describe the source process • Special attention should be paid to the directivity • Source complexity • Static displacement (asperity) • Rupture velocity • Slip velocity

  5. Numerical Green‘s Function • Theory • Optimal largest subfault size • Study area and fault • Database created

  6. Numerical Green‘s Function Theory

  7. Numerical Green‘s Function Optimal subfault size – homogeneous case Accuracy increases with the increase of • cut-off frequency • rupture velocity • magnitude

  8. Numerical Green‘s Function Study area N SCEC cvm version3

  9. Numerical Green‘s Function Grant and Shearer, 2004 SCEC cfm Newport Inglewood Fault M6.4 Long Beach earthquake in 1933 (Hauksson and Gross, 1991) Probable source for a damaging earthquake Near-vertical plane and predominant right-lateral slip (SCEC cfm)

  10. Numerical Green‘s Function Verification – heterogeneous case subfault size 1.5 km can be applied as the principal subfault size to the generation of the NGF data base

  11. Numerical Green‘s Function Database

  12. Summary 1 • Equation for synthesization of NGFs is developed. • Optimal subfault size is investigated both for homogeneous media and heterogeneous media. • Database is created for the Newport Inglewood fault embedded in the Los Angeles basin with appropriate setup.

  13. Uncertainty - Hypocentre Outline • Motivation • Hypocentre locations • Velocity snapshots • Basin amplification • PGV characteristics variation with hypocentre location

  14. Uncertainty - Hypocentre Static displacement and hypocentres Guatteri et al., 2005

  15. Uncertainty - Hypocentre Velocity snapshots

  16. Uncertainty - Hypocentre Velocity Profiles

  17. Uncertantity - Hypocentre PGV characteristics

  18. Uncertantity - Hypocentre Varying source depth

  19. Summary 2 • Horizontal hypocentre variation influences the ground motion • Vertical hypocentre variation has only slight influence on the ground motion • In the area far from the fault, the medium plays main role on ground motion variation while in the area very close to the fault plane the hypocentre does

  20. Uncertainty - Slip Outline • Quasi-dynamic rutpure process generation • Directivity effect • Slip variation effect • PGV characteristics

  21. Uncertantity - Slip Guatteri et al., 2005 Quasi-dynamic rutpure process

  22. Uncertantity - Slip Wang et al., 2006, submitted to ESG

  23. Uncertantity - Slip Somerville et al., 1997 Aki & Richards, 2002 Directivity

  24. Uncertantity - Slip Different directivity on different components the fault perpendicular component is dominated by the directivity effect and the fault parallel and vertical components have significant contribution from the 3-D structure (basin effects) and slip distribution. Wang et al., 2006, submitted to ESG

  25. Uncertantity - Slip Three individual slips Wang et al., 2006, submitted to ESG

  26. Uncertantity - Slip PGV characteristics: maximum value and standard deviation Wang et al., 2006, submitted to ESG

  27. Summary 3 • Directivity effect dominates the fault perpendicular component • Fault parallel and vertical components have significant contribution from the 3-D structure (basin effects) and slip distribution. • Slip asperity elevates the ground motion in its nearby area. • The maximum seismic motion variation on the surface is dominated by directivity.

  28. Conclusions We investigate the ground motion variations due to sets of parameters using our new-developed method Numerical Green’s Function… • Horizontal hypocentre location variations influence the ground motion. • Dominant directivity effect on the fault perpendicular component is confirmed by our simulations while fault parallel components are controled by both the source properties and the basin structure, for this specific case. • Slip asperity elevates the ground motion in its nearby area. • The maximum seismic motion variation on the surface is dominated by directivity.

  29. Future Works • Investigation of rotational motions • Peak rotational motions • Attenuation relations for rotations • Source vs. 3D effects for rotations

  30. End Thanks

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