برآورد نرخ وقوع زمین‌لرزه بر اساس تغییر شکل پوسته ایران

نوع مقاله : مقاله تحقیقی‌ (پژوهشی‌)

نویسندگان

1 دانشجوی دکتری، پژوهشگاه زلزله شناسی و مهندسی زلزله، تهران، ایران

2 استاد، پژوهشگاه زلزله شناسی و مهندسی زلزله، تهران، ایران

3 Postdoctoral researcher, ETH, Zurich, Switzerland

چکیده

فلات ایران یکی از مناطق لرزه‌خیز در جهان است که در بیشتر نواحی آن، دوره بازگشت زمین‌لرزه­های بزرگ بیش از 1000 تا 2000 سال است. اغلب، برآورد نرخ وقوع زمین‌لرزه با استفاده از آمار زمین‌لرزه­های ثبت­شده در کاتالوگ­‌های لرزه‌ای صورت می­پذیرد؛ بنابراین هرچه این کاتالوگ­ها به واقعیت نزدیک­تر باشند، برآورد نرخ وقوع نیز واقع‌بینانه­تر است. عواملی چون کامل نبودن کاتالوگ­ها، دوره بازگشت بلند­‌مدت زمین‌لرزه­های بزرگ و ثبت دستگاهی کوتاه­مدت ناکافی (در حدود صد سال) باعث برآورد نه‌چندان مطمئن نرخ وقوع‌ زمین‌لرزه­ها می­شود. به­منظور کاهش عدم‌ قطعیت­های موجود در برآورد نرخ وقوع زمین‌لرزه­ها و افزایش اعتماد به نتایج، امروزه از مدل­های نوین توسعه­یافته استفاده می­شود که ورودی آنها ترکیب داده­هایی مانند اطلاعات لرزه­خیزی، زمین­شناسی و ژئودتیکی است. این مدل­های نوین می­توانند باعث افزایش دانش و پاسخ به مسائل مرتبط با توزیع مکانی- زمانی زمین‌لرزه­ها و کاهش عدم قطعیت نتایج شوند؛ ازاین‌رو با توجه به لرزه­خیزی کشور ایران و کاستی­های اطلاعات زمین‌لرزه­های ثبت­شده، هدف از این پژوهش برآورد نرخ وقوع مبتنی بر تغییر شکل پوسته ایران برای اولین بار است. برای‌این­منظور از نتایج مدل تغییر ‌شکلی جامع فلات ایران استفاده شد که خروجی اصلی آن نرخ کرنش پیوسته است. در این مطالعه نرخ کرنش به‌دست­آمده از اطلاعات تغییر ‌شکلی، به ممان لرزه‌ای و سپس نرخ وقوع زمین‌لرزه­ها تبدیل شده است. مقایسه نرخ وقوع مبتنی بر تغییر شکل با برآورد نرخ وقوع بلند­‌مدت مبتنی بر کاتالوگ­های موجود نشان می­دهد در تمام ایالت­های لرزه­زمین‌ساخت ایران، نرخ وقوع مبتنی بر تغییر شکل بیش از نرخ وقوع مبتنی بر کاتالوگ است که می­تواند تأثیر چشمگیری در نتایج برآورد خطر لرزه‌ای داشته باشد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Estimation of earthquake occurrence rate based on the crust deformation of Iran

نویسندگان [English]

  • Alireza Lotfi 1
  • Hamid Zafarani 2
  • Alireza Khodaverdian 3
1 International Institute of Earthquake Engineering and Seismology, Tehran, Iran.
2 Professor, International Institute of Earthquake Engineering and Seismology, Tehran, Iran
3 Postdoctoral researcher, ETH, Zurich, Switzerland
چکیده [English]

The Iranian Plateau is one of the most seismically active regions in the world, where the recurrence time of large-magnitude events is often more than a thousand years. The Mw 7.3, 1990 Rudbar earthquake, which caused 40,000 deaths and 500,000 homeless, and the Mw 6.5, 2003 Bam earthquake, which caused around 26,000 losses and 30,000 wounded, are two of the largest and the most destructive earthquakes in the region. Seismic hazard assessment is useful in the classification of areas that are more prone to earthquake losses. The earthquake occurrence rate is an important factor in seismic hazard analysis, which is commonly based on the earthquake catalogs. Hence, providing complete and reliable catalogs is necessary to achieve more accurate estimates. Unfortunately, factors such as the incompleteness of catalogs, the long-term recurrence time of large earthquakes, and the inadequate short-term instrumental record of about 100 years have resulted in unreliable earthquake occurrence rates estimates. To reduce uncertainties, some models have been developed for some places in the world such as California, Canada, Japan, New Zealand, and Italy based on the combination of various data as inputs, such as seismicity information, geological data such as fault slip rates, and geodetic information such as GPS data. The utilization of these models can increase the knowledge about the spatio-temporal distribution of earthquakes and reduce the uncertainty of results. The purpose of this study is to convert the strain rate into the earthquakes occurrence rate for some zones in Iran. Strain rates are derived from the available comprehensive deformation model of the Iranian Plateau, in which the long-term crustal flow of the Iranian Plateau is computed by using various data sets, including the latest fault traces, geologic fault offset rates, GPS velocities, principal stress directions, and velocity boundary conditions. In the comprehensive deformation model of the Iranian Plateau, based on the existing information on relative displacement of geologic features, the long-term geological offset rates for 33 of 171 fault traces were collected as input. Moreover, geodetic velocities of 239 GPS benchmarks were considered. Comparison with the results of the existing catalogs shows that for the whole Iranian Plateau, the occurrence rate based on strain is higher than the occurrence rate based on the catalog. We expect that utilizing the occurrence rate based on strain in the hazard model in further studies can have a significant effect on the ground motion parameters for Iran in comparison with previous catalog-based seismic hazard assessments.
 

کلیدواژه‌ها [English]

  • Iranian Plateau
  • Deformation model
  • Seismic moment rate
  • Strain Rate
  • Earthquake occurrence rate
 
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