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Seismotectonic Variables in Japan, Turkey and Canada

Seismotectonic Variables in Japan, Turkey and Canada

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  • Over the 10-40km scale range the larger value of D in the region of compression suggests that differences observed over the full range are primarily associated with variations occurring at larger 10-40km scales.
  • No correlation was observed between b, D2, D15, and GPS strain.

KFUPM 2004 KFUPM 2004 Presentation Transcript

  • Ali O. Oncel Earth Science Department of KFUPM Seismological studies: evaluating linkages between seismotectonic variables in Japan, Turkey and Canada
    • Earthquake Magnitude/Space/Fault Statistics
    • Correlations of seismicity and faulting in Japan
      • (Oncel, Wilson, Nishizawa, 2001, Journal of Geophysical Research)
    • Disturbing stress changes and asperity for Tohoku earthquake area
      • (Oncel and Aydan, 2004)
    • Geodetical strain and earthquake hazard: Example from western Turkey
      • (Oncel and Wilson, 2004, in press, JGR)
    • Coulomb stress and aftershocks: Example from western Canada
      • (Oncel, 2002, American Geophysical Union)
    Contents of Presentation
  • Log N = a – bM Earthquake Magnitude/Space Statistics
    • D (Fractal dimension)-value :
    • D 2 >D 3 >……>D 15  heterogeneous
    • D 2 =D 3 =……=D 15  homogeneous
    • D high …………….>Declustering or dispersion
    • D low ……………..>Clustering or localization
    • b-value :
    • Material heterogeneity
    • Applied shear stress level
    • b high ……> creeping
    • B low …….> asperity
  • If pattern has fractal properties then N = Cr -D N :the number of occupied boxes r: the length of the box (r). Fault Statistics
  • Active Fault Analysis in Japan
  • Seismicity Analysis in Japan
  • Correlation between faulting and seismicity
  • Negative Correlations : Stress suddenly released of larger magnitude seismicity on interconnected faults of larger total surface Positive Correlations: Stress is gradually released by lower magnitude seismicity on smaller fault strands. Tohoku Events: July 26 event (M=6.2) were located in a positive correlation (Area III) noted to be anomalously quiescent. Correlations of seismotectonic variables 5.00 to 6.00 6.00 to 7.00 1998-2003 M=6.2 2003.07.26 M=5.5 2003.07.26
  • displacement rate Almost 1000 stations in Japanese Islands daily measurement of location with accuracy of 1[cm] GPS Earth Observation Network (GEONET)
  • Aftershocks of July 26, 2003 (M w =6.0) GPS-local stations
    • Strain rates (Aydan, 2002, 2003)
    Average Strain Rates computed by using 1 st -order derivative from displacements Coordinate system and the definition of displacement rates for a triangular element Displacements Strain rates Strain rates
  • stress rate tensor computed by using Hooke’s law from the computed strain rates for elastic materials. Maximum Shear Stress + * Mean Stress Rate Disturbing Stress Rate= Friction of coefficient ( =0.8) Lame’s Constants ≈ 30 GPa [Fowler, 1990] Strain rates
  • Disturbing stress changes and asperity
  • Contour maps of GPS derived shear and dilatation are shown in the maps above (middle and right maps, respectively). GPS strains were derived by Kahle et al. (2000) from GPS velocity data presented by McCloskey et al. (2000) for the western Turkey and eastern Mediterranean area examined in this paper. Average shear and dilatation in each seismic zone were estimated by averaging contour values of shear and dilatation observed on the regular grid of points highlighted in the map above. GPS control points are shown along with events of magnitude M>3.0 recorded between 1981 and 1998. The 25 seismic zones into which the area was subdivided for analysis and comparison are also outlined. Geodetical strain and earthquake hazard: Example from western Turkey
  • The study area was divided into three regional tectonic subdivisions consisting of a region of shear in the north associated with the Northern Anatolian Fault Zone (NAFZ), a region dominated by extension in the back-arc region of central Turkey, and a region of compression along the Aegean subduction zone. Seismotectonic parameters (D q and b) and geodetic strains (shear and dilatation) are shown in the table at right for each of the 25 seismic zones. Local Variations of Complex Variables
  • Median/mean values of multifractal correlation dimensions D 2 and D 15 are tabulated for the full range, 2 to 10km range and 10 to 40 km range for each tectonic subdivision of the study area (shear, extension, and compression). The median/mean values of b, shear, and dilatation are also listed for each tectonic region. Over the full range : D 2 measured in the region of compression is statistically greater than D 2 in the regions of extension and shear. D 15 is less than D 2 in all cases . Over the 2-10 km scale : Statistically significant differences between regions are not observed. Over the 10-40km scale : The larger value of D in the region of compression suggests that differences observed over the full range are primarily associated with variations occurring at larger 10-40km scales . Regional comparison between seismicity and GPS strain
  • The correlation coefficient, r = 0.81 The probability (p) that the slope of the regression line could actually be zero is 0.026 in this case. Cross-plot of b values and D 2 from the Northern Anatolian Fault Zone
    • Over the full range: A significant positive correlation is observed between seismic clustering (D) and the Gutenberg-Richter b value along the NAFZ strike slip zone.
    • Over the 10 -40 km scale: A nearly significant relationship between b and D is observed (r = 0.74, p = 0.06) and suggests that the relationship is primarily associated with deeper or regional scale seismicity since significant correlation is not observed over the 2 to 10 km scale .
    • No correlation was observed between seismicity ( b, D 2 , D 15 ) and GPS strain .
    Correlation between seismicity and GPS strain
  • Afterthoughts on the Izmit Earthquake Increased b and decreased D C suggest that the rise in the level of low magnitude seismicity and high intensity clustering along the western portion of NAFZ did not completely release stress transferred into this segment of the fault zone ( Oncel et al., 1995, Non.Lineer.Geophysics; Oncel and Wilson, 2001, BSSA ). This combination of factors - westward migration along with increased levels of low magnitude seismicity and higher intensity seismic clustering - are indicators of increased seismic risk in the area.
    • Over the 2-10 km scale: Significant correlation is not observed between seismic clustering and dilatation.
    • Over the full range: Significant correlation between b and D is not observed.
    • Over the 10 -40 km scale: In this subdivision, seismic clustering (D 2 and D 15 ) correlate positively with dilatation (r = 0.67 and 0.73 with p = 0.02 and 0.01 respectively). The correlations suggest that increased rates of extension produce increasingly dispersed seismicity.
    Correlation between seismicity and GPS strain
    • One would expect seismicity to correlate moreso with dilatation in a subduction zone. However, dilatation along the subduction zone is on average only slightly negative.
    • Dilatation is positive in the areas to the northeast (17 nstrain/a) and negative (-29 nstrain/a) farther west along the subduction zone. This combination of positive and negative dilatation along the subduction zone is probably responsible for the lack of a more significant correlation between b and dilatation.
    • The change of dilatation from positive to negative as one goes east to west along the subduction zone suggests a transition in plate interaction from transtensional to transpressive .
    • Over the full range: Variations of b value correlate negatively with shear (r = -0.83, p = 0.04) in the zones of this subdivision. The correlation of b to dilatation is weakly positive (r = 0.73, p = 0.1).
    Correlation between seismicity and GPS strain
  • Coulomb Stress Modelling Illustration of the Coulomb stress change (King, 1994). The panels show a map view of a vertical strike-slip fault embedded in an elastic half-space, with imposed slip that tapers toward the fault ends. Stress changes are depicted by graded colors; green represents no change in stress. (A) Graphical representation of equation 8 of King et al (1994), a “specified fault” calculation. (B) Graphical presentation of equation 13 of King et al., (1994), for optimally-oriented strike-slip “opt strike-slip” faults.
  • Coulomb stress and aftershocks: Example from western Canada