1. © Anomalous Seismicity Preceding The 1999 Izmit Event, NW Turkey Oncel, AO; Wilson, T BLACKWELL PUBLISHING, GEOPHYSICAL JOURNAL INTERNATIONAL; pp: 259- 270; Vol: 169 King Fahd University of Petroleum & Minerals http://www.kfupm.edu.sa Summary The 1999 Izmit earthquake (1999 August 17, M-w = 7.4) was one of the largest earthquakes to occur in northwestern Turkey during the past 100 yr. This earthquake occurred along the Izmit-Sapanca fault within the Northern Anatolian Fault Zone. Variations in the generalized fractal dimensions (D-q) of clustering in time and space, the Gutenberg-Richter b-value, and earthquake frequency (N) are evaluated in detail over an 8.5 yr time period preceding the Izmit event. Spatial and temporal comparisons of the variations in these parameters reveal anomalous intermediate term behaviour over shorter timescales than previously observed. Significant correlation is observed between changes in b-value with the spatial and temporal fractal dimension of epicentre distribution. These correlations oscillate back and forth over 2-3 yr time intervals and suggest occurrence of significant instability in the nature of intermediate-term deformation along the fault zone. Seismotectonic behaviour immediately preceding the Izmit event is represented by a significant rise in b-value to a maximum of 2.26 accompanied by relatively small increases in D. The rapid rise of b is associated with an increased frequency of low magnitude seismicity. Although D (spatial and temporal) increase slightly in the 2-3 yr period preceding rupture, they remain less than 1 indicating that seismicity remains clustered prior to rupture. In areas where earthquake frequency or station density do not permit resolution of short- term variations of fractal scaling parameters within a few months of main rupture, an accelerated period of low-magnitude seismicity (high b-value) concentrated along a fault zone (D < 1) may suggest heightened probability of a forthcoming large event. Copyright: King Fahd University of Petroleum & Minerals; http://www.kfupm.edu.sa

2. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. © References: AKI K, 1965, B EARTHQ RES I TOKYO, V43, P237 AMBRASEYS N, 2002, B SEISMOL SOC AM, V92, P1 AWATA Y, 2003, SURFACE RUPTURE ASSO, P41 BAKER GL, 1990, CHAOTIC DYNAMICS INT CASTELLARO S, 2006, GEOPHYS J INT, V165, P913, DOI 10.1111/j.1365-246X.2006.02955.x EVANS R, 1982, GEOPHYS J ROY ASTRON, V69, P284 EVANS R, 1985, GEOPHYS J ROY ASTRON, V83, P47 FIELDER G, 1974, TECTONOPHYSICS, V23, P277 GODANO C, 1995, GEOPHYS J INT, V121, P385 GRASSBERGER P, 1983, PHYSICA D, V9, P189 GUTENBERG B, 1954, SEISMICITY EARTH ASS HENDERSON J, 1992, GEOPHYS RES LETT, V19, P365 HENDERSON J, 1992, J STRUCT GEOL, V14, P905 HENDERSON J, 1994, PURE APPL GEOPHYS, V19, P545 ITO A, 2002, B SEISMOL SOC AM, V92, P418 JAUME SC, 1999, PURE APPL GEOPHYS, V155, P279 KAGAN YY, 1991, GEOPHYS J INT, V104, P117 KAGAN YY, 1994, J GEOPHYS RES-SOLID, V99, P13685 KAHLE HG, 2000, J GEOPHYS RES-SOL EA, V105, P23353 KARAKAISIS GF, 2003, GEOPHYS J INT, V153, P103 KOSTROV BV, 1974, IZV EARTH PHYS, V1, P23 LEI XL, 1999, GEOPHYS J INT, V139, P754 LEI XL, 2000, J GEOPHYS RES-SOL EA, V105, P6127 MAIN I, 1996, REV GEOPHYS, V34, P433 MAIN IG, 1989, GEOPHYS J-OXFORD, V96, P131 MAIN IG, 1989, TECTONOPHYSICS, V167, P273 NAKAYA S, 2002, GEOPHYS RES LETT, V29, ARTN 1495 OLSSON R, 1999, J GEODYN, V27, P547 ONCEL AO, 1995, NONLINEAR PROC GEOPH, V2, P147 ONCEL AO, 1996, PURE APPL GEOPHYS, V147, P147 ONCEL AO, 1999, MICROSEISMICITY MARM, P40 ONCEL AO, 2000, GEOPHYS J INT, V143, P501 ONCEL AO, 2000, IZMIT DUZCE EARTHQUA, P1 ONCEL AO, 2002, B SEISMOL SOC AM, V92, P339 ONCEL AO, 2004, J GEOPHYS RES-SOL EA, V109, ARTN B11306 ONCEL AO, 2006, TECTONOPHYSICS, V418, P205, DOI 10.1016/j.tecto.2006.02.006 SCHOLZ CH, 2002, EARTHQUAKES FAULTING SHAH KR, 1995, J GEOPHYS RES-SOL EA, V100, P15527 SHAW BE, 1992, J GEOPHYS RES, V97, P479 SHAW BE, 1993, GEOPHYS RES LETT, V20, P907 SMALLEY RF, 1987, B SEISMOL SOC AM, V77, P1368 Copyright: King Fahd University of Petroleum & Minerals; http://www.kfupm.edu.sa

3. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. © SMITH WD, 1981, NATURE, V289, P136 SMITH WD, 1986, GEOPHYS J ROY ASTRON, V86, P815 STEACY SJ, 1999, GEOPHYS RES LETT, V26, P899 SUNMONU LA, 2001, J GEOL SOC INDIA, V58, P163 TOKSOZ MN, 1979, PURE APPL GEOPHYS, V117, P1258 UCER SB, 1985, GEOPHYS J ROY ASTRON, V83, P17 VINCIGUERRA S, 2002, J VOLCANOL GEOTH RES, V113, P391 WARD SN, 1994, B SEISMOL SOC AM, V84, P1293 WESTERHAUS M, 2002, GEOPHYS J INT, V148, P139 WIEMER S, 2000, B SEISMOL SOC AM, V90, P859 WIEMER S, 2001, SEISMOL RES LETT, V72, P373 For pre-prints please write to: oncel@hotmail.com Copyright: King Fahd University of Petroleum & Minerals; http://www.kfupm.edu.sa