ویژگی‌های لرزه‌زمین‌ساختی گسل‌های باختر و جنوب بلوک لوت با تأکید بر رسیدگی ساختاری و تحلیل فرکتالی آنها

نوع مقاله : Articles

نویسندگان

1 پژوهشکده زلزله‌شناسی، پژوهشگاه بین‌المللی زلزله‌شناسی و مهندسی زلزله، تهران، ایران

2 گروه لرزه‌زمین‌ساخت، سازمان زمین‌شناسی و اکتشافات معدنی کشور، تهران، ایران

چکیده

با استفاده از پارامترهای قطعه­‌بندی، درازای گسیختگی (در طی هر زمین‌لرزه)، میزان جابه­‌جایی بر روی گسل­ها و الگوی تکرار رویداد زمین‌لرزه‌ها؛ رسیدگی ساختاری گسل­های باختر و جنوب بلوک لوت مورد ارزیابی قرار گرفتند. در این مطالعه طیف پاسخ جنبش زمین‌لرزه‌های بزرگ روی‌داده در منطقه، تحلیل شدند. بر اساس نتایج حاصله، گسل کوهبنان: نارس؛ بم: میانه تا نارس؛ گوک، لاله‌زار، کهورک: رسیده می­باشند.در بحث تحلیل فرکتالی و رشد و بلوغ پهنه­‌های گسلی منطقه، از روش مربع شمار استفاده شد. بر اساس محاسبات انجام شده، بُعد فرکتالی گسل­های کوهبنان و شاخه­های جنوبی آن، گسل­های بم، کهورک، فاریاب، چاه مزرعه (اسفندقه) و گوک نسبت به بقیه گسل­ها کمتر است. در امتداد این گسل‌ها، رومرکز زمین‌لرزه‌ها تمرکز بیشتری دارند. بُعد فرکتالی با نزدیک شدن به حاشیه داخلی بلوک لوت افزایش پیدا می­کند. این افزایش نشان از بالا بودن پراکندگی میدان تنش در این منطقه است. بُعد فرکتالی سامانه گسلی نایبند (721/1-56/1) و گسل سبزواران باختری (68/1-52/1) از شمال به جنوب کاهش و گسل گوک (68/1-52/1) از شمال به جنوب افزایش پیدا می­کند. بر این اساس قطعات جنوبی سامانه گسل نایبند و سبزواران باختری و قطعات شمالی سامانه گسلی گوک نارس­تر می­باشند و توان ایجاد خطر لرزه­ای جدی­تری را دارند. بر اساس نتایج حاصله از مبحث رسیدگی ساختاری و بررسی ابعاد فرکتالی، لرزه­خیزترین گسل­های منطقه گسل­های کوهبنان، بم، کهورک، گوک، لاله‌زار، فاریاب و چاه مزرعه (اسفندقه) می‌باشند.

کلیدواژه‌ها


عنوان مقاله [English]

Seismotectonic Characteristics of the Faults in the S, W Lut Block by Structural Maturity and Fractal Dimension

نویسندگان [English]

  • Ahmad Rashidi 1
  • Nayereh Sabour 2
1 Seismological Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
2 Geological Survey and Mineral Explorations of Iran, Tehran, Iran
چکیده [English]

The study area is located in the W-S Lut block. Eleven destructive earthquakes, from 1977 to 2012, were accompanied by about 185 km of the surface rupture in the South and Southwest of the Lut block. These earthquakes have resulted in ~44,700 human fatalities, ~36,646 injured and more than 100,000 homeless. In the western and southern margins of the Lut Block, there is a complete absence of historical records of earthquakes up until ~160 years ago. This lack of records may be resulted from the isolation of the area due to proximity to deserts (Ambraseys and Melville, 2005; Berberian, 2005). Nevertheless, some historical earthquakes for the pre-1900 period are reported (e.g. Berberian, 1977; Ambraseys et al., 1979; Berberian et al., 1979; Ambraseys and Melville, 2005). There is no reliable estimation of the seismotectonic characteristic in this region; therefore, the seismic hazard assessment is not accurate enough. It is important that the seismicity of the area and its temporal and spatial variations are viewed as snapshots of the ongoing tectonic activities. Therefore, identification of the structural maturity and fractal dimension may provide complementary deductions for more realistic analysis and interpretation of the observations.
We investigated a number of faults in this area that have high potential for generating destructive earthquakes. The faulting patterns appear to preserve different stages of fault development. We investigated the distribution of active faults and the role that they play in accommodating tectonic strain in the SW-Lut.
For interpretation of structural maturity, we used fault segmentation, rupture length, displacement on the fault surface and pattern of repetition of the earthquake event. Based on the results of this study, the Kuhbanan fault is immature, the bam fault is middle until immature and Gowk, Lalehzar, and Kahourak are mature.
For the fractal analysis and the maturity of the fault zones in the area, we used fractal dimension. Based on the calculations, the fractal dimension of the Kuhbanan fault and its southern branches, Bam, Kahourak, Faryab, Chahmazrae (Esfandaqeh) and Gowk faults are less than the other faults in the study area. Along these faults, the focal mechanism of the earthquakes are more focused. Inner edge of the Lut block, the fractal dimension are increasing. This increase show high distribution of stress in this area. The dispersion of the stress field decreased the amount of stress and seismic activity in this area.
The fractal dimension of the Nayband fault system (1.56-1.72) and West Sabzevaran fault (1.52-1.68) reduce from north to south and Gowk fault (5.15-1.68) increase from north to south. Therefore, the southern part of the Nayband and West Sabzevaran faults and the northern parts of the Gowk fault are immature. These area have serious risk for the area.
Based on the results of structural maturity and fractal dimensions, Kuhbanan, Bam, Kahourak, Gowk, Lalehzar, Faryab and Chahmazrae (Esfandaqeh) faults will create high risk of seismicity.
References

Ambraseys, N.N., Arsovski, M., and Moinfar, A.A. (1979) The Gisk Earthquake of 19 December 1977 and the Seismicity of the Kuhbanan Fault-Zone. UNESCO.
Ambraseys, N.N. and Melville, C.P. (2005) A History of Persian Earthquakes. Cambridge University Press.

Berberian, M. (1977) Contribution to the seismotectonics of Iran (Part II-III). In: Commemoration of the 50th Anniversary of the Pahlavi Dynasty.


Berberian, M., Asudeh, I., and Arshadi, S. (1979) Surface rupture and mechanism of the Bob-Tangol (southeastern Iran) earthquake of 19 December 1977. Earth Planet Sci. Lett., 42(3), 456e462.


Berberian, M. (2005) The 2003 Bam urban earthquake: a predictable seismotectonic pattern along the western margin of the rigid Lut block, southeast Iran. Earthq. Spectra, 21(S1), 35e99, https://doi.org/10.1193/1.2127909.

کلیدواژه‌ها [English]

  • Structural Maturity
  • Seismic Behavior
  • Surface Rupture
  • Fractal Analysis
  • Seismotectonics
  • Response Spectrum
  • Lut Block
  • Iran
  1. Foroutan, M., et al. (2014) Late Pleistocene-Holocene right slip rate and paleo-seismology of the Nayband fault, western margin of the Lut block, Iran. J. Geophys. Res. [Solid Earth] 119 (4), 3517e3560.
  2. Walker, R.T., Talebian, M., Sloan, R.A., Rasheedi, A., Fattahi, M., Bryant, C. (2010) Holocene slip-rate on the Gowk strike-slip fault and implications for the dis-tribution of tectonic strain in eastern Iran. Geophys. J. Int. 181 (1), 221e228.
  3. Regard, V., Bellier, O., Braucher, R., Gasse, F., Bourles, D., Mercier, J., Thomas, J.-C., Abbassi, M.R., Shabanian, E., Soleymani, S. (2006) 10 Be dating of alluvial de-posits from Southeastern Iran (the Hormoz Strait area). Palaeogeogr. Palae-oclimatol. Palaeoecol. 242 (1), 36e53.
  4. Rashidi, A., Khatib, M.M., Mousavi, S.M., Jamour. Y. (1396) Estimation of the active faults Based on: Seismic, Geologic and Geodetic Moment Rates . Scientific Quarterly Journal, Geosciences. 26 (104), 211-222 (In persian)..
  5. Aghanabati, A. (1385) Geology of Iran. Geological survey of Iran. Tehran. Iran (In persian).
  6. Rashidi, A., Khatib, M.M., Raeesi, M., Mousavi, S.M., Djamour, Y. (2018) Geometric-kinematic characteristics of the main faults in the W-SW of the Lut Block (SE Iran). Journal of African Earth Sciences. 139, 440-462
  7. Manighetti, I., Campill, M., Bouley, S., & Cotton, F. (2007) Earthquake scaling, fault segmentation, and structural maturity. Earth and plantary science letters, 253, 429- 438.
  8. Radiguet, M., Cotton,F., Manighetti, M., Campillo, M., & Douglas, J. (2009) Dependency of Near-Field Ground Motions on the structural maturity of the ruptured faults. Bulletin of Seismological Society of America, 99 (4).
  9. Saboor, N., Ghassemi. M.R., Eskandari, M., Nazari, A., Ghorashi. M., Seenaian. F. (2015) Structural maturity of active faults and evolutionary pattern of seismic activity in eastern Iran. 24 (95), 57-66 (In persian).
  10. Turcotte D.L. (1986) A fractal approach to the relationship between ore grade and tonnage, Eam. Gal., 81, 1528-1530.
  11. King, G., & Yielding, G. (1984) initiation propagation and termination in the 1980 EL Asnam (Algeria) earthequack. G.J-R.A S, 77 ( 3), 915-933.
  12. King, G. (1986) Speculation on the geometry of the initiation and termination process of earthequack rupture and its relation to morphology and geological structure. Pure Appl. Geoph, 124, 567-585.
  13. Turcotte, D.L. (1992) Fractals, chaos, self-organized criticality and tectonics. Terra Neva, 4, 4-12.
  14. Sukmono, M. T. Z., Hendrajaya, L. Kadir, W. G. A., Santoso, D., & Dubois, J. (1997) Fractal pattern of the Sumatra fault seismicity and its possible APP.
  15. Liu-Zeng, J., Heaton, T., & DiCaprio, Ch.. (2005) The effect of slip variability on earthquake slip-length scaling, Geophys. J. Int, 162, 841-849.
  16. Boore, D. M., Joyner,W. B., & Fumal, T. E. (1997) Equations for estimating horizontal response spectra and peak acceleration from western North American earthquakes: a summary of recent work. Seismological Research Letters, 68(1), 128-153.
  17. Berberian, M. (2014) Earthquakes and Coseismic Surface Faulting on the Iranian Plateau: Elsevier, 699p.
  18. Fattahi, M., Walker, R.T., Talebian, M., Sloan, R.A., & Rasheedi, A. (2011) The structure and late Quaternary slip rate of the Rafsanjan strike-slip fault, SE Iran. Geosphere. 7, 1159–1174.
  19. Walker, R., Jackson, J., & C. Baker. (2003) Surface expression of thrust faulting in eastern Iran: source parameters and surface deformation of the 1978 Tabas and 1968 Ferdows earthquake sequences, Geophys. J. Int., 152, 749-765.
  20. Sukmono, M. T. Z., Hendrajaya, L. Kadir, W. G. A., Santoso, D., & Dubois, J. (1997) Fractal pattern of the Sumatra fault seismicity and its possible APP.
  21. Mandelbrot. B. B. (1982) "The Fractal Geometry of Nature" 460. PP., W. H. Freeman, San Francisco, Calif., 1982.
  22. Khatib, M.M. (1377) Geometry of end branches in strike slip faults. Thesis for the Degree of Doctor of Geology in Tectonics. University of Shahid Beheshti (In persian).