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GSJ  2004
 

GSJ 2004

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Geodetical Strain and Seismicity in Japan

Geodetical Strain and Seismicity in Japan

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    GSJ  2004 GSJ 2004 Presentation Transcript

    • The relationship of geodetic strain to seismicity on the island arc of Japan Ali O. Oncel Geological Survey of Japan
    • cc
      • Previous Research
      • A) Fault Complexity/Magnitude Intrerrelationship
      • B) Seismic Cluster/Magnitude Interrrelationship
      • C) GPS-strain and Seismicity
      Contents of Presentation
    • FRACTAL ANALYSIS OF FAULTING (Oncel, Wilson and Nishizawa, JGR-2001) Correlation coefficients between b and D S computed along lines 1-3 are contoured to illustrate the spatial distribution of positive and negative correlation regions (areas 1-3) throughout Japan If pattern has fractal properties then N = Cr -D N :the number of occupied boxes r: the length of the box (r).
    • Seismic b-value (Oncel, Wilson and Nishizawa, JGR-2001) Correlation coefficients between b and D S computed along lines 1-3 are contoured to illustrate the spatial distribution of positive and negative correlation regions (areas 1-3) throughout Japan b=2.303/(M mean -M min +0.05)
      • Space-time variability
      • of b -value can be effected by several physical factors such as:
      • Material heterogeneity
      • Applied shear stress level
      • Coulomb failure stress
      • Thermal gradient
      • Fault complexity
      • Local scale 0.5 and 1.6.
      • Regional scale equal to 1.
       
    • Fractal Analysis of Seismicity (Oncel, Wilson and Nishizawa, JGR-2001)
      • 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
    • Correlations of seismotectonic variables (Oncel, Wilson and Nishizawa, JGR-2001) Active faults in Japan digitized from the 1:200,000 active fault maps produced by the Research Group for Active Faults of Japan (1991).
    • Mapping the correlations of seismotectonic variables (Oncel, Wilson and Nishizawa, JGR-2001) Correlation coefficients between b and D S computed along lines 1-3 are contoured to illustrate the spatial distribution of positive and negative correlation regions (areas 1-3) throughout Japan 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. 5.00 to 6.00 6.00 to 7.00 1998-2003 M=6.2 2003.07.26 M=5.5 2003.07.26
    • Temporal variations of Seismicity (Oncel et al.,PAGEOPH-1996, Oncel and Wilson, BSSA-2001)
    • Temporal variations of Seismicity (Oncel et al.,Nonlinear Geophys-1995, Oncel and Wilson.BSSA-2001)
    • Spatial variations of Seismicity (Oncel et al., Tectonophysics-1996, Oncel and Wilson, BSSA-2001)
    • GPS and Earthquake Mechanism Reilinger, Toksoz and Barka, GSA-2000 We know that changes in the recent deformation observed by GPS measurement reveals dependence on fault type and velocity field. Velocity is lower for lateral motion while it is observed to be higher for vertical motion. Relationships between GPS derived deformation rate and Seismic Hazard has not, as yet, been proposed.
    • GPS and Hazard Parameters Modified after (Oncel and Wyss, 2000) Changes in GPS measurement seems to be partially related to the fault patches of seismic (asperity) and aseismic (creep). Especially, GPS velocity vectors is smaller in northern strand of NAFZ indicating higher seismic hazard while observing larger in its southern strand.
    • Contour Map of the 10 year Area Strain Data (Wilson, Kano, and Nishizawa, in revision, PAGEOPH)
    • Contour Map of the 100 year Area Strain Data (Wilson, Kano, and Nishizawa, in revision, PAGEOPH)
    • Correlations of seismotectonic variables Station locations from which horizontal crustal strain measurements were made. Active faults in Japan digitized from the 1:200,000 active fault maps produced by the Research Group for Active Faults of Japan (1991).
      • The Main Objective: to evaluate the relationship of geodetic strain to hazard parameters such as earthquake seismicity distribution, rate and magnitude.
      • Research Plan:
      • Correlation will be investigated for the two different periods of short (1883-1994) and long (1985-1994).
      • Correlation between strain data and hazard parameters will be computed locally along transects similar to those shown in Figures 3 and 4 of (Oncel, Wilson and Nishizawa, 2001).
      What we propose?
    • Interrelationship between seismotectonic variables and geodetic strain
      • Positive correlation: could indicate anomalous behavior in the form of 1) gradual stress release in the form of relatively small magnitude earthquakes on the one hand or 2) stress buildup followed by sudden release of larger amounts of stored energy.
      • Negative correlation: could arise through increases of b associated with decreases in e or vice versa. Negative correlations seem to best fit our expectations .
      • No correlation: are likely to occur in transitions from positive to negative correlation or in areas where the fluctuations of individual parameters are random and statistically insignificant