برآورد نرخ لغزش گسلهای پیرامون بم و کاربرد آن در ارزیابی خطر زمینلرزه

نوع مقاله: مقاله پژوهشی

نویسندگان

1 پژوهشکده علوم زمین، سازمان زمینشناسی و اکتشافات معدنی کشور، تهران، ایران

2 مرکز تحقیقات ساختمان و مسکن، وزارت مسکن و شهرسازی، تهران، ایران

3 موسسه ژئوفیزیک دانشگاه تهران، تهران، ایران

4 پردیس دانشکدههای فنی، دانشگاه تهران، تهران، ایران

چکیده

فلات ایران با قرار‌گیری بین دو صفحه عربی و اروپا-آسیا، سالانه حدود 22 میلی‌متر کوتاه‌شدگی در راستای شمال- جنوب دارد. حدود 9 میلی‌متر از این کوتاه‌شدگی سبب چین‌خوردگی و گسل‌خوردگی در زاگرس می‌شود و باقی‌مانده آن به‌طور عمده در البرز و کپه داغ جای می‌گیرد. بلوک مرکزی ایران تغییر شکل اندکی دارد بنابراین، متناسب با میزان کوتاه‌شدگی در البرز و کپه داغ، با سرعت حدود 13 میلی‌متر در سال به  سوی شمال حرکت می‌نماید. در خاور ایران،  بلوک صلب و پایدار افغانستان قرار دارد که حرکت چندانی نسبت به اوراسیا ندارد بنابراین حرکت به سوی شمال ایران مرکزی نسبت به بلوک افغانستان تنش برشی راست‌گردی را در خاور ایران ایجاد می‌نماید که به ترتیب حدود 8  و 5  میلی‌متر در سال آن در راستای گسل‌های خاور و باختر دشت لوت جای می‌گیرند. یکی از مشکلات برآورد خطر زمین‌لرزه در خاور ایران کمبود داده‌های زمین‌لرزه‌ای، ژئودتیک و ناشناخته بودن نرخ لغزش گسل‌ها است. از این رو در این پژوهش سعی شده است تا به کمک داد‌ه‌های موجود زمین‌شناسی و سن‌یابی مطلق شیوه توزیع حرکت راستالغز بر روی گسل‌‌های این ناحیه تا حدودی برآورد شود. در ادامه با توجه به اهمیت گسل بم- براوات و گسل زمین‌لرزه‌ای جنوب بم در برآورد خطر زمین‌لرزه در شهر بم  این گسل به طور خاص مورد  مطالعه قرار گرفته است. نمونه‌گیری از آبرفت‌های برخاسته در اثر جنبش گسل بم- براوات در انتهای جنوبی این گسل، و تعیین سن مطلق آنها به روش لومینسانس نوری، نرخ برخاستگی حدود 5/0 میلی‌متر در سال را برای این گسل مشخص می‌نماید. از آن جا که جنبش این گسل از نظر هندسی با گسل جنوب بم در ارتباط است، بنابراین به کمک این سن‌یابی نرخ لغزش راستالغز راستگرد گسل جنوب بم نیز حدود 2 میلی‌متر در سال بر آورد می‌شود .  
 

کلیدواژه‌ها


عنوان مقاله [English]

Estimating Slip Rates of Faults around Bam and their Application in Evaluation of Earthquake Hazard

نویسندگان [English]

  • M. Talebian 1
  • S. H. Tabatabaei 2
  • M. Fattahi 3
  • M. Ghorashi 1
  • A. Beitollahi 2
  • A. Ghalandarzadeh 4
  • M.A. Riahi 3
1 Research Institute for Earth Sciences, Geological Survey of Iran, Tehran, Iran
2 Building and Housing Research Center, Tehran, Iran
3 Institute of Geophysics, University of Tehran, Tehran, Iran
4 University College of Engineering, University of Theran, Theran, Iran
چکیده [English]

The Iranian plateau lies between the Arabian and Eurasian plates and accommodates approximately 22 mm/yr of N-S shortening.  About 9 mm/y of this shortening is taken up by folding and thrusting in the Zagros while the remaining 13 mm/yr is taken up in the Alborz and Kopeh-Dagh. The Central Iran block is relatively stable and thus moves to the north with an average velocity of about 13 mm/y. As the stable Afghanistan block lies to the east, the northward motion of Central Iran produces a right-lateral shear in eastern Iran, which is distributed mainly over a few major faults to the west (~5 mm/yr) and east (~ 8 mm/yr) of the Lut desert. Limited information is available about the slip rates of individual faults in eastern Iran; therefore in this study we try to combine all geological, geodetic and available Quaternary dating results to estimate the fault slip rates and distribution of active deformation in eastern Iran. Finally, we report the results from OSL dating of samples taken from uplifted plain deposits near the south end of the Bam-Baravat fault. These results show that this fault is growing in the vertical direction with at a rate of ~ 0.5 mmy-1. Considering geometric relation between the Bam-Baravat and the south Bam earthquake fault, we estimate a slip rate of about 2 mm/y for the south Bam earthquake fault. 

کلیدواژه‌ها [English]

  • Bam
  • Earthquake
  • Iran
  • Slip Rate
  • Fault
 

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