ارزیابی توان لرزه‌خیزی پهنه لوت با مقایسه نرخ گشتاورهای ژئودتیک، لرزه‌ای و زمین‌شناسی

نوع مقاله : Articles

نویسندگان

1 دانشگاه بیرجند

2 گروه زمین شناسی، دانشگاه بیرجند

3 پژوهشگاه بین‌المللی زلزله شناسی و مهندسی زلزله، تهران

چکیده

نرخ گشتاور بیانگر میزان انرژی است که در سامانه‌های دگرریختی صرف می‌شود و به سه روش ژئودتیکی، لرزه­شناسی و زمین‌شناسی به دست می­آید. در این پژوهش پهنه‌ی لوت به پنج ناحیه ساختاری تقسیم شده است. بیشترین مقدار نرخ گشتاور به‌دست‌آمده مربوط به گشتاور ژئودتیک می‌باشد که برابر با Nm/yr 1019×2118/1 می‌باشد. نرخ گشتاور لرزه‌ای Nm/yr 1018×9456/3 و در نهایت نرخ گشتاور زمین‌شناسی نیز معادل  Nm/yr1016×4882/2 محاسبه شد. مقایسه نرخ گشتاور ژئودتیک و لرزه‌ای نشان می‌دهد دگرشکلی بین لرزه‌ای در پهنه لوت 07/3 برابر دگرشکلی لرزه‌ای در این منطقه می‌باشد. نسبت نرخ گشتاور لرزه‌ای به ژئودتیک در ناحیه‌های 1 تا 5 به‌ترتیب برابر با 69/0، 55/0، 36/2، 03/0 و 02/0 برآورد شده است که نشان می‌دهد واتنش در بخش‌های شمالی سریع و در بخش‌های جنوبی کند می‌باشد. نسبت نرخ گشتاور زمین‌شناسی به لرزه‌ای نشان می‌دهد 63/0 درصد از کل انرژی پتانسیل موجود در گسل‌ها به‌صورت زمین‌لرزه در طی کاتالوگ زمین‌لرزه‌ای آزاد شده است و بخش زیادی از انرژی همچنان باقی است و می‌تواند در آینده آزاد شود. با بررسی نرخ‌های گشتاور ژئودتیک، لرزه‌ای و زمین‌شناسی در ناحیه‌های مختلف پهنه لوت، به نظر می‌رسد خطرناک‌ترین بخش پهنه لوت از لحاظ پتانسیل لرزه‌خیزی ناحیه جنوب خاور لوت باشد که منطبق بر سیستم گسل نهبندان از جنوب گسل آبیز تا مرزهای جنوبی پهنه‌ی لوت می‌باشد.

کلیدواژه‌ها


عنوان مقاله [English]

Estimation of the Seismicity Potential, Based on Geodetic, Seismic and Geological Moment Rate in the Lut Block

نویسندگان [English]

  • Saeed Zarei 1
  • Mohamad Mehdi Khatib 2
  • Mehdi Zare 3
  • Seyed Morteza Moussavi 2
1 Department of Geology, Faculty of Science, University of Birjand
2 Department of Geology, Faculty of Science, University of Birjand, Birjand
3 International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
چکیده [English]

The Lut Zone, with about 900 km length, is in the eastern part of central Iran. The eastern boundary of this zone is specified by the Nehbandan fault and the eastern Flysch of Iran and its western border by the Nayband fault and the Tabas block. East of Iran consists of a series of strike-slip and step-down faults that are fractured-crustal deformable and its evolution is influenced by processes that dominated on the strike-slip shear zones. In other words, the potential energy accumulated in this region is used as a slip along the strike-slip faults of the region, folding and non-slip creep.
Earthquake occurrence rates are an essential part of seismic-hazard analysis. Estimate of moment rate is comparatively reckoned as a new method for dealing with tectonic activities rate in different regions and it prepares the way for putting together different methods. There are now three major types of data available to estimate these occurrence rates: Geodetic moment rate, seismic moment rate (on the basis of historical and instrumental earthquake data) and geologic moment rate are estimated for Lut block in east of Iran. Lut block was affected by several large earthquakes in the past causing heavy damage in this region. Each approach has limitations, but in principle they should all yield similar estimates.
Firstly, a catalog of historical and instrumental earthquakes was used. Then, while preparing the fault maps of the region, regarding the geometric information of the active faults, the latest information on the geometrical characteristics of the faults has been collected. Finally, geological, seismic and geodetic moment rates for the region were estimated and the results were compared. Depending on the type of deformation and geometry of fault, the study area divided to the five zones: northwestern (zone 1), southwestern (zone 2), north and northeastern (zone 3), southwestern (zone 4) and southern zone (zone 5). Then we compare the value of three types of moment rate in these zones to each other. The most moment rate in the Lut block belongs to geodetic approach (1.2119x1018 Nm/yr) and then seismic moment rate (3.9455x1018 Nm/yr), and finally the least quantity belongs to geologic moment rate (2.4882x1016 Nm/yr).
Each of these calculating methods of moment bring from a different perspective that can show different patterns in the style and extent of tectonic activity in the region. Geodetic moment rates include both seismic and non-seismic deformations and cover a highly short time range. Therefore, it is obvious that it shows higher values than the other two methods. The most of seismic moment rate was obtained respectively in Zone 3, 1, 4, 5 and 2. According to seismic map, maximum seismic moment is along Abiz, Dasht-e Bayaz and Tabas Faults. These faults are responsible for large earthquakes in the study area. Maximum geologic moment rate is related to West-Neh, East-Neh, Kahoorak, Abiz and Nosrat-abad Faults. According to values of geological and geodetic moment rates in the southeastern of Lut area and based on the value of the release seismic energy in the north and western part of Lut area, it seems that in the next time, the most of seismic potential and seismic hazard are in the southeastern part of the study area.
According to the ratio of seismic to geodetic moment rate can be concluded that the northern part and northwestern part with ratio 2.36 and 0.69 are fast strain areas and south, southwestern and southeastern part with ratio: 0.055, 0.02 and 0.03 are fast strain areas, respectively. Ratio of the geodetic moment rate to the seismic moment rate obtained more than 3.07, which reflects the important role of the interseismic deformation in this area. Ratio of seismic moment rate to geological moment rate is 0.63 %. This value indicates that 0.63 % potential of the faults for seismic energy has been released ant not been released a significant part of the elastic energy in the area.

کلیدواژه‌ها [English]

  • Seismicity Potential
  • Seismic Moment Rate
  • Geodetic Data
  • Lut Block
  1. Agard, P. Omrani, J. Jolivet, L. and Mouthereau, F. (2005) Convergence history across Zagros (Iran): constraints from collisional and earlier deformation, Int. J. Earth Sci., 94, 401–419.
  2. Jackson, J.A. and Mckenzie, D.P. (1984) Active tecnonics of the Alpine- Himalayan belt between Turkey and Pakistan. Geophys. J. R. Aster. Soc., 77, 185-264.
  3. Chu, D. and Gordon, R.G. (1998) Current plate motions across the Red Sea. Geophys. J. Int., 135, 313-328.
  4. DeMets, C., Gordon, R., Argus, D.F., and Stein, S. (1994) Effects of recent revisions to the geomagnetic time scale on estimates of current plate motion, Geophy. Res. Let., 21, 2191-2194.
  5. Jackson, J.A., Haines, J. and Holt, W. (1995) The accommodation of Arabia-Eurasia ‎Plate convergence in Iran. J. Geophy. Res., 100, 15205-15219.
  6. Vernant, Ph., Nilforoushan, F., Hatzfeld, D., Abassi, M.R., Vigny, C., Masson, F., Nankali, H., Martinod, J., Ashtiani, A., Bayer, R., Tavakoli, F., and Chery, J. (2004) Present-day crustal deformation and plate kinematics in the Middle East constrained by GPS measurements in Iran and Northern Oman, Geophy. J. Int., 157, 381-398.
  7. Walker, R. and Jackson, J. (2004) Active tectonics and late Cenozoic strain distribution in central and eastern Iran. Tectonics, 23, TC5010, doi:10.1029/2003TC001529.
  8. Meyer, B. and Le Dortz, K. (2007) Strike-slip kinematics in Central and Eastern Iran: estimating fault slip-rates averaged over the Holocene. Tectonics, 26, TC5009.
  9. Le Dortz, K., Meyer, B., S´ebrier, M., Nazari, H., Braucher, R., Fattahi, M., Benedetti, L., Foroutan, M., Siame, L., Bourles, D., Talebian, M., Bateman, M.D., and Ghoraishi, M. (2009) Holocene right-slip rate determined by cosmogenic and OSL dating on the Anar fault, Central Iran. Geophy. J. Int., 179, 700-710.
  10. Foroutan, M., Meyer, B., Sebrier, M., Nazari, H., Murray, A.S., Le Dortz, K., Shokri, M.A., Arnold, M., Aumaître, G., Bourlès, D., Keddadouche, K., Solaymani Azad, S., and Bolourchi, M.J. (2014) Late Pleistocene-Holocene right slip rate and paleoseismology of the Nayband fault, western margin of the Lut block, Iran, J. Geophys. Res., 119, 3517-3560.
  11. Walker, R.T., Khatib, M.M., Bahroudi, A., Rodes, A., Schnabel, C., Fattahi, M., Talebian, M., and Bergman, E. (2013) Co-seismic, geomorphic, and geologic fold growth associated with the 1978 Tabas-e-Golshan earthquake fault in eastern Iran, Geomorphology, http://dx.doi.org/ 10.1016/j.geomorph.2013.02.016.
  12. Berberian, M. and Yeats, R.S. (2001) Contribution of archaeological data to studies of earthquake history in the Iranian Plateau. J. Str. Geo., 23, 563-584.
  13. Ward, S.N. (1998) On the consistency of earthquake rates, geological fault data, and space geodetic strain: the United States, Geophys. J. Int., 134, 172-187.
  14. Pancha, A., Anderson, J.G., Kreemer, C. (2006) Comparison of seismic and geodetic scalar moment rates across the Basin and Range province. Bull. Seismo. Soc. Am., 96, 11-32.
  15. Kreemer, C., Chamot-Rooke, N., and Pichon, X.L. (2004) Constraints on the evolution and vertical coherency of deformation in the Northern Aegean from a comparison of geodetic, geologic and seismologic data, Ear. and Pla. Sci., 225, 329-346.
  16. Newman, A.V., Dixon, T.H., Ofoegbu, G.I., and Dixon, J.E. (2001) Geodetic and seismic constraints on recent activity at Long Valley Caldera, California: evidence for viscoelastic rheology. Volca. Geoth. Res., 105, 183-206.
  17. Angelica, C., Bonforte, A., Distefano, G., Serpelloni, E., and Gresta, S. (2013) Seismic potential in Italy from integration and comparison of seismic and geodetic strain rates. Tectonophysics, 608, 996-1006.
  18. Asadi Sarshar, M., Bahroudi, E.M.A., Ghoreshi, M., Ghasemi, M.R. (2010) Comparison of Seismic, Geodetic and Geologic Moment Rates in Central Alborz. Geosci. J., 9, 19-24.
  19. Talebian, M. (2012) Comparison of Seismic, Geodetic and Geologic Moment Rates in Eastern Alborz and Kopeh Dagh. Geos. J., 86, 183-192.
  20. Zarei, S., Moridi Farimai, A.A., Oveisi, B., Khatib, M.M., Mohamadkhani, S. (2013) Comparison of Geologic, seismic and Geodetic Moment Rate in the Central Zagros. J. Env. Geol.
  21. Berberian, M. (2014) Earthquakes and Co-seismic Surface Faulting on the Iranian Plateau. Elsevier, 699.
  22. Ambraseys, N.N., Melville, C.P. (1982) A history of Persian earthquakes: Cambridge University Press, Britain, Translated by Abolhassan Radeh, Agah Publishers, Tehran, 1991.
  23. Hanks, T.C. and Kanamori, H. (1979) A moment magnitude scale. J. Geophys. Res., 84, 2348-2350.
  24. Ekstrom, G.A. (1987) A Broad Band Method of Earthquake Analysis. Ph.D. Thesis, Harvard University, Cambridge.
  25. Jahnston, A. (1996) Seismic moment assessment of earthquakes in stable continental regions-III. New Madride 1811-1812, Chaleston 1886 and Lisbon 1755. Geophy. J. Int., 126, 314-344.
  26. Kanamori, H. (1977) Seismic and aseismic slip along subduction zones and their tectonic implications. Maurice Ewing Ser., 1, 162-174.
  27. Heaton, T.H., Tajima, F., and Mori, A.W. (1986) Estimating ground motions recorded accelerograms. Surveys in Geophysics, 8, 25-83.
  28. Rezapour, M. (2003) Analysis of archived data and assessment of magnitude seismic networks in Tehran. Earth and Space Physics (JESP), 29, 55-65.
  29. Ward, S.N. (1998) On the consistency of earthquake moment release, and space geodetic strain: Europe. Geophy. J. Int., 135, 1011-1018.
  30. Engdahl, E.R., Jackson, J.A., Myers, S.C., Bergman, E.A., and Priestley, K. (2006) Relocation and assessment of seismicity in the Iran region. Geophys. J. Int., 167, 761-778.
  31. Scordilis, E.M. (2006) Empirical global relations converting MS and mb to moment magnitude. J. Seismol., 10, 225-236.
  32. Shoja-Taheri, J., Naserieh, S., and Ghofrani, H. (2007) ML and MW scalein the Iranian Pelateau base on the strong motion records. Bull. Seism. Soc. Am., 97(2), 661-669.
  33. Kostrov, B.V. (1974) Seismic moment assessment and energy of earthquakes, and seismic flow of rock. Acad. Sci. USSR Phys. Solid Earth, 1, 23-40.
  34. Zarifi, Z., Nilfouroushan, F., and Raeesi, M. (2013) Crustal stress map of Iran: insight from seismic and geodetics computations. Pure and Applied Geophysics, 171, 1219-1236.
  35. Wells, D.L., Coppersmith, K.J. (1994) Empirical relationships among magnitude, rupture length, rupture area, and surface displacement. Bull. Seismo. Soc. Am., 84, 974-1002.
  36. Walker, R.T., Talebian, M., Sloan, R.A., Rashidi, A., Fattahi, M., and Bryant, C. (2010) Holocene slip-rate on the Gowk strike-slip fault and implications for the distribution of tectonic strain in eastern Iran. Geophys. J. Int., 181, 221-228.
  37. Walpersdorf, A., Manighetti, I., Mousavi, Z., Tavakoli, F., Vergnolle, M., Jadidi, A., Hatzfeld, D., Aghamohammadi, A., Bigot, A., Djamour, Y., Nankali, H., and Sedighi, M. (2014) Present-day kinematics and fault slip rates in eastern Iran, derived from 11 years of GPS data. J. Geophys. Res., 119, 1-25.
  38. Tavakoli, F. (2007) Present-Day Kinematics of the Zagros and East of Iran Faults. Ph.D. Thesis, Univ. of Joseph Fourier, Grenoble, France.
  39. Molnar, P., Dayem, K.E. (2010) Major intracontinental strike-slip faults and contrasts in lithospheric strength. Geosphere, 6, 444-467.
  40. Khodaverdian, A., Zafarani, H., and Rahimian, M. (2015) Long term fault slip rates, distributed deformation rates and forecast of seismicity in the Iranian Plateau. Tectonics, 34, 2190–2220, doi:10.1002/2014TC003796.
  41. Mohajjel, M. (2009) Thin-skinned deformation near Shahdad, southeast Iran. J. Asian Earth Sci., 36, 146-155.
  42. Yazdanpanah, H., Khatib, M.M., Nazari, H., Gholami, E. (2015) Analysis of strike-slip kinematcs a shear zone with heterogeneous slip rate: case study Lut area, eastern Iran. Geosciences J., 25, 279-290.