سنجش کمی توزیع مکانی_ زمانی پس‌لرزه‌های زمین‌لرزة 1385 درب آستانه ( سیلاخور)، باختر ایران

نوع مقاله: مقاله پژوهشی

نویسندگان

بخش علوم زمین، دانشکدة علوم، دانشگاه شیراز

چکیده

زمین‌لرزة 11 فروردین 1385(31 مارس 2006م) با بزرگای گشتاوری 1/6، روستاهای منطقة درب آستانه (سیلاخور) در استان لرستان را ویران کرد. ناحیة رومرکزی این رویداد در قلمرو زون گسل اصلی معاصر(Main Recent Fault,MRF)  و سازوکار راستالغز راستگرد آن نیز مشابه دیگر زمین‌لرزه‌های این سامانة گسلی است. این زمین‌لرزه با پسلرزه‌های نسبتاً  فراوانی همراه بوده که در این تحقیق، توالی پسلرزه‌های آن با استفاده از معیارهای کمی ضریب تغییرات (coefficient of variations,Cv)، توان تابع چگالی طیفی(power spectral density) و ابعاد فراکتالی تعمیم یافته (generalized fractal dimensions) مورد مطالعه قرار گرفته است. شاخصهای کمی محاسبه شده حاکی از وجود ساختار فراکتالی (fractal structure) در توزیع زمانی و مکانی پسلرزه‌های این زمین‌لرزه است. مشاهدة رفتار فراکتالی علاوه بر تأیید وجود خوشه‌بندی در توزیع پسلرزه‌ها، دلیلی بر ناهمگنی وضعیت زمین‌شناسی و ژئودینامیکی منطقة کانونی زمین‌لرزه نیز هست. نتایج به دست آمده نشان می‌دهد با گذشت زمان ابعاد چندفراکتالی توالی زمانی پسلرزه‌ها کاهش و ابعاد چندفراکتالی مراکز سطحی آنها افزایش یافته است. به نظر می‌رسد این تغییرات ناشی از تغییر رژیم تنش زمین‌ساختی و تأثیر گسلهای فرعی و همراه (secondary and sympathetic faults) باشد. نتایج به دست آمده همچنین دلالت بر کاربرد مؤثرتر روش چندفراکتالی نسبت به روشهای فراکتالی ساده برای مطالعه رفتار خوشه‌بندی فرایند پسلرزه‌ای دارد. 

کلیدواژه‌ها


عنوان مقاله [English]

Quantification of the Spatial-Temporal Distribution of Aftershocks Associated with the 2006 Darb-e-Astaneh (Silakhor) Earthquake, western Iran

نویسندگان [English]

  • A. Zamani
  • M. Agh-Atabai
Earth Sciences Department, Faculty of Sciences, Shiraz University
چکیده [English]

The 31 March, 2006 earthquake with Mw=6.1 destroyed villages in the Darb-e-Astaneh (Silakhor) region of the Lurestan province. The epicenteral area of this earthquake lies near the Main Recent Fault (MRF) and its right lateral mechanism indicates that it belongs to this fault zone. The main shock was followed by relatively large number of aftershocks. In this research, the aftershock sequence of this earthquake has been studied by measuring quantitative indices of coefficient of variations (CV), the exponent of the power spectral density function, and the generalized multifractal dimensions. The results reveal the presence of fractal structure in the temporal and spatial distribution of aftershock sequence. The multifractal behavior of the aftershock sequence indicates the clustering of the earthquake activity and the degree of the heterogeneity in the seismotectonic and geodynamic processes in the focal region. The results show that the multifractal dimensions of the aftershock sequence decreases and the multifractal dimensions of aftershock epicenters increases with time. It seems that these changes in the multifractal dimensions are related to the activity of secondary and sympathetic faults and changes in the tectonic stress regime of the region. The results also indicate that the multifractal method rather than monofractal approaches is a powerful tool for quantitative analysis of aftershock process's clustering behavior.                     

کلیدواژه‌ها [English]

  • Earthquake
  • Multifractal method
  • Tectonics
  • Neotectonics
  • Seismotectonics
  • Seismicity
  • Iran

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