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DPRI seminar

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2003 Tokachi-Oki Earthquake

2003 Tokachi-Oki Earthquake


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  • 1. Seismic source characterization defined by minima of local recurrence time before the 2003 MJ8.0 Tokachi-Oki Earthquake Ali O.Oncel Geological Survey of Japan, AIST-Tsukuba
  • 2. Principles
    • b-value :
    • Material heterogeneity
    • Applied shear stress level
    • Coulomb failure stress
    • Thermal gradient
    • Fault complexity
    T L (M) = dT/10 (a-bM) Log N = a - bM a-value: Activity rate TL(M): Probabilistic recurrence time P L (M) = 1/T L* A PL(M): Annual local probability
  • 3. Major asperities defined by microseismicity (Oncel and Wyss, Geophysical Journal International-2000) T L (M) = dT/10 (a-bM) Izmit rupture is initiated by the asperity “ Area I ” but stopped at its western end by another asperity “ Area II ” that acted as a barrier in a stated of low stress.
  • 4. Temporal variations of Seismicity (Oncel et al.,PAGEOPH-1996, Oncel and Wilson, BSSA-2001)
  • 5. Temporal variations of Seismicity (Oncel et al.,Nonlineer Geophysics-1996, Oncel and Wilson, BSSA-2001)
  • 6. Geodetical strain and earthquake hazard: Example from western Turkey Oncel and Wilson, 2004
  • 7.
    • The spectrum of the generalized fractal dimensions ( D q , q = 0,1,2,....) of seismicity data is determined by Correlation Integral.
    • Estimated from the linear portion of the log-log plot of C q versus distance, can be used to evaluate the distribution for multifractal behavior.
    • D 2  Regional scale
    • D 15  Local scale
    • D 2 >D 3 >……>D 15  heterogeneous
    • D 2 =D 3 =……=D 15  homogeneous
    Multifractal Dimensions (Dq ) Oncel and Wilson, 2004
  • 8. Comparison between b-value/Fractal Dimension and GPS strain Oncel and Wilson, 2004
  • 9. Active faults in Japan digitized from the 1:200,000 active fault maps produced by the Research Group for Active Faults of Japan (1991). Correlations of seismotectonic variables (Oncel, Wilson and Nishizawa, Journal of Geophysical Research-2001)
  • 10. Tohoku Events: Recent seismic events in the Tohoku region (M=5.5 and 6.2) were located in a positive correlation (Area III) noted to be anomalously quiescent. These intermediate magnitude events caused considerable damage and were characterized by higher than normal intensity for earthquakes of this magnitude. Negative Correlations : Observed in the areas accommodates rupture on interconnected faults of larger total surface and therefore larger seismic moment. Positive Correlations: Observed in the areas where stress is released by lower magnitude seismicity on smaller fault strands. Correlations of seismotectonic variables (Oncel, Wilson and Nishizawa, Journal of Geophysical Research-2001) 5.00 to 6.00 6.00 to 7.00 1998-2003 M=6.2 2003.07.26 M=5.5 2003.07.26
  • 11. Disturbing stress changes and asperity Oncel and Aydan, 2004
  • 12. Coulomb stress and aftershocks: Example from western Canada (Oncel, 2002)
  • 13. Case Study: Tokachi-Oki Rupture Area (Yamanaka and Kikuchi, 2003)
  • 14. Case Study Approach Correlation of T L -minima of recent seismicity (1997 – 2003) with the locations and number of asperities defined by strong motion modelling (Kamae and Kawabe) Kamae and Kawabe (2003)
  • 15. Tokachi-Oki Rupture Area (0-100KM)
  • 16. Depth distribution
  • 17. For T L <30 yr Sa: Combined Asperity Area=325 Km 2 S: Total Fault Area=3581 Km 2 Sa/S=0.09 For T L <30 yr Sa: Combined Asperity Area=1075 Km 2 S: Total Fault Area=34 Km 2 Sa/S=0.5 For T L <30 yr Sa: Combined Asperity Area=300 Km 2 S: Total Fault Area=3293 Km 2 Sa/S=0.09 %9 %34 %9
  • 18. Size changes asperity in depth: Approach The size of asperity through the edge of fault plane is decreasing? Should it be related to size-scaling changes of seismicity? Increase or decrease in size of asperity is supposed to be related to the local recurrence changes? Test: Compute the TL for different subregions through the dipping plane of fault and compare the size changes of seismicity with the rate changes of seismicity.
  • 19. Inland crustal earthquake Irikura and Miyake (2001) Sa: Combined Asperity Area S: Total Fault Area Sa/S = 0.22 Da: Average Slip on Asperities D: Average Slip on Total Fault Da/D = 2.0 (Somerville et al., 1999)  c : Average stress drop  a : Stress drop on asperity Relation between Combined Asperity Size (Sa) and Total Rupture Area (S) Irikura and Miyake (2001) Key of outer fault parameters
  • 20. %9 For T L <30 yr Sa: Combined Asperity Area=325 Km 2 S: Total Fault Area=3581 Km 2 Sa/S=0.09 B A
  • 21. %34 For T L <30 yr Sa: Combined Asperity Area=1075 Km 2 S: Total Fault Area=34 Km 2 Sa/S=0.5 B A
  • 22. %9 For T L <30 yr Sa: Combined Asperity Area=300 Km 2 S: Total Fault Area=3293 Km 2 Sa/S=0.09 B A