SSA 2002
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This study examined relationships between multifractal properties of earthquake distributions (Dq), b-values, and plate velocities in western Turkey and the eastern Mediterranean. Positive correlations were found between D and b-values over 10-40km scales along the North Anatolian Fault Zone, but not in extensional or subduction zones. In extensional regions, increased plate velocity was linked to lower b-values and more dispersed seismicity. Differences in relationships between tectonic settings could relate to rupture mechanisms or plate velocities.
SSA 2002
- 1. The Relationship of Microplate Velocity to Seismotectonic Variables: An Example from Western Turkey and the Eastern Mediterranean Ali.O.Oncel Geological Survey of Canada (East) Thomas Wilson West Virginia University
- 2. Data Sources and Regions GPS derived plate velocity vectors (from McClousky et al., 2000) M>3.0 ( 40km)/1981 and 1998/ 25 subdivisions (N>100)/M min (2.6-3.8)
- 3. Seismic b-value Computed using the maximum likelihood method (Aki, 1965) M MEAN is the mean magnitude of events M>M min 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.
- 4. Multifractal Dimensions (D q ) 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
- 5. Scale Transitions in the Patterns of Earthquake Seismicity Fractal analysis of scaling relationships observed in patterns of seismicity and fracture systems often reveal the presence of scale transitions (for example, Wesnousky, 1994; Scholz, 1994 a and b; Scholz, 1994a, 1997a-b, 1998; Sornette and Sornette, 1993; Kagan, 1996; Bonnett et al ., 2000; Main et al ., 1999; Main, 2000; Wilson, 2001). In this study we also examine the log ( C r ) vs. log( r ) plots for changes of slope with scale ( r ). Examples of slope variations with scale in the regions of compression and extension will be shown in the following slides. These transitions were not observed in all seismic zones, and they do not always occur at the same value of r .
- 6. Examples from the Regions of Compression and Extension 2.5 3 3.5 4 4.5 5 5.5 10 0 10 1 10 2 Magnitude Cumulative Number b-value (w LS, M > 3.5): -0.671 +/- 0.08, a-value = 4.1116 b-value (max lik, M > 3): -0.887 +/- 0.11, a-value = 4.9569 80 85 90 95 0 50 100 150 200 250 300 350 Time in years Cumulative Number Region 19 Region 13 Aftershocks Cluster A Cluster B Cluster A Cluster B Background Aftershocks 25 o E 10' 20' 30' 40' 6' 12' 18' 38 o N 24.00' 30' 36' 42' 24 o E 30' 25 o E 30' 26 o E 30' 30' 45' 37 o N 15' 30'
- 7. Regional Variations of Complex Variables Examination of all log ( C r ) vs. log( r ) plots often reveals the presence of slope transitions in the 5 to 20 km range. In this study we also examine the behavior of D 2 and D 15 over the 2 to 10 km and 10 to 40 km range to determine if systematic differences exist in the behavior of the log ( C r ) vs. log( r ) plots at local and more regional scales. We then evaluate correlations between D at the 2 to 10 and 10 to 40 km scales with b and V and compare these correlations to those obtained between the full scale estimates of D with b and V. The t-test was used to evaluate the significance of differences between the different measures of fractal dimension.
- 8. Local Variations of Complex Variables
- 9. Interrelationships observed along the NAFZ PPositive correlation (r = 0.74 and 0.77) between D and b over 10 to 40km scales ( level = 0.05) . Statistically significant relationships between D and V , and V and b were not observed.
- 10. Interrelationships in the Hellenic Back-Arc Region D and b are not correlated A negative correlation ( r =-0.7) is observed between b and V ( = 0.01) . A positive correlation ( r =0.52 and 0.61) over full-range is observed between D 2 and D 15 with V ( = 0.09 and 0.03, respectively) .
- 11. Interrelationships along the Hellenic Subduction Zone The correlations between D 2 and D 15 with b -value are 0.51 and 0.71, respectively, however, neither of these is statistically significant ( = 0.30 and 0.12). Marginal negative correlation ( r = - 0.71) between b and V ( = 0.12). No significant correlations between D and V, and D and b.
- 12. We examined interrelationships between multifractal properties of epicenter distributions ( D q ), the Gutenberg-Richter b -value, and plate velocity ( V ) in the eastern Mediterranean and western Turkey region. The study area contains three major tectonic elements The NAFZ The Hellenic Back-Arc, and Hellenic Subduction Complex Summary
- 13. Earthquakes incorporated in the study included only those occurring between 1981 and 1998. Summary D q ( q = 2 through 15), b -value and V were computed in each of the 25 seismic subdivisions of the area. Scale transitions were common in the log C(r) versus log r correlation integrals. D varies with scale. Separate estimates of D 2 and D 15 were made over the 2 to 10 km and 10 to 40 km scales.
- 14. Interrelationships observed along the NAFZ PPositive correlation between D and b over 10 to 40km scales SStatistically significant relationships between D and V , and V and b were not observed. The result suggests that larger magnitude earthquakes (larger b value) are associated with more dispersed (less clustered, higher D ) distributions of earthquakes. TThe correlation between D and b is observed only along the NAFZ.
- 15. The increased positive correlation between D and b along the NAFZ may be a useful hazard indicator since positive correlation characterizes the 20 year period preceding the Izmit earthquake and stands in sharp contrast to the negative correlation between D and b observed along the western segment of the NAFZ from 1945 to 1975 (Oncel and Wilson, 2002). Afterthoughts on the Izmit Earthquake
- 16. Negative Positive Afterthoughts on the Izmit Earthquake The correlation between D and b over the 1981 through 1998 time period reveals a continued increase in the positive correlation. The correlation of D 2 and D 15 with b -value, over the more recent 17 year time period, increases to 0.81 and 0.73 respectively.
- 17. Afterthoughts on the Izmit Earthquake Whether the tendency to positive correlation between D and b observed in the region of shear is indicative of increased contemporary seismic hazard is unknown, an analysis of the spatial variations of D , V , b -value, a -value, and T L currently in progress, may provide additional insights into seismic hazard assessment.
- 18. D and b are not correlated A negative correlation is observed between b and V A positive correlation is observed between D and V Interrelationships in the Hellenic Back-Arc Region These relationships suggest that in areas deformed by extension, increased plate velocity results in an increased probability of larger magnitude seismicity (lower b value). The tendency to positive correlation between D and V suggests that as velocity increases, epicenter distributions become less clustered.
- 19. Marginal positive correlation between b and V No correlations between D and V, and D and b Interrelationships along the Hellenic Subduction Zone
- 20. General Conclusions Negative correlation between b and V in tectonic regions undergoing extension and compression suggest that when plates converge or diverge at higher velocity, these regions will be accompanied by higher magnitude seismicity. WWe note that in the region of extension there is a tendency to negative correlation between D and b , while in the region of compression this relationship tends to be positive. WWe speculate that in regions of compression, increased plate velocity is associated with a tendency to have increasingly clustered seismicity, whereas in regions undergoing extension, this relationship may be reversed, i.e., increased plate velocity tends to be associated with more dispersed patterns of seismicity.
- 21. General Conclusions Relationships observed along the NAFZ are distinctly different. These differences may, in some way be associated with the lower average plate velocity along the NAFZ compared to the other regions (~ 17mm/yr versus ~28 mm/yr). TThe origin of the differences in relationships between the region of shear, and regions of extension and compression is unknown. They may arise because of differences in rupture mechanism, to differences in plate velocity, or to a combination of both.
- 22. General Conclusions Interrelationships between complex seismotectonic variables ( b -value, the multifractal properties of epicenter distribution) and microplate velocity, differ with tectonic setting. Future studies of the spatial and temporal variations in these relationships with activity rates and local recurrence times may provide useful measures of seismic hazard.