ارزیابی تغییرات تنش لرزه‌ای در پهنه مکران

نوع مقاله : مقاله پژوهشی‌

نویسندگان

1 استادیار، پژوهشکده زلزله‌شناسی، پژوهشگاه بین المللی زلزله‌شناسی و مهندسی زلزله، تهران، ایران

2 کارشناس ارشد، پژوهشکده زلزله‌شناسی، پژوهشگاه بین المللی زلزله‌شناسی و مهندسی زلزله، تهران، ایران

چکیده

پهنه مکران با طولی متجاوز از 900 کیلومتر در جنوب خاور ایران و جنوب پاکستان، تنها بخش از فلات ایران است که در آن پوسته اقیانوسی صفحه عربی با شیب کم به‌سوی شمال، به زیر پوسته قاره­ای ایران فرورانش دارد. مکران بین دو پهنه برخوردی قاره­ای-قاره­ای زاگرس و هیمالیا، محصور شده است. فرورانش پوسته اقیانوسی در راستای سطوح گسلی با شیب به‌سمت شمال از کرتاسه آغازین شروع شده است. با توجه به فعالیت زمین‌ساختی، ادامه فرورانش و وجود پهنه گسلی–راندگی با درازای بالا در بخش شمالی فرورانش مکران و حاشیه شمالی دریای عمان، موجب گردیده است که این منطقه از خطرپذیری بسیاربالایی متأثر از وقوع زمین­لرزه­ای قوی و سونامی ناشی از آن برخوردار باشد. در این مطالعه نوار مکران با در نظرگرفتن پارامتر­های لرزه­خیزی در نظر گرفته شده در رابطه گوتنبرگ-ریشتر، مورد ارزیابی قرار گرفت. به‌عبارتی ویژگی آماری زمین‌‌لرزه‌‌ها با در نظرگرفتن توزیع فضایی و زمانی آنها لحاظ شد. به‌همین منظور داده­های پایه مرتبط با گسلش و لرزه‌‌خیزی به‌همراه بزرگای زمین‌لرزه‌ها، مورد بررسی قرار گرفت. پایه و اساس این آنالیز تعیین پارامتر لرزه‌‌خیزی (b) بود که بر اساس محاسبه توزیع-فراوانی بزرگا و انتگرال همبستگی محاسبه گردید. در این روش توزیع زمانی و فضایی پارامترها، ویژگی تجمعی داده‌ها و سطح تنش زمین­ساختی منطقه مرتبط با فرایندهای مختلف لرزه‌زمین‌ساختی متفاوت از دیگر روش‌ها لحاظ شده است. به‌منظور محاسبه این پارامترها از داده‌های لرزه­ای مختلف (پایگاه­های داخلی و خارجی) استفاده گردید. با در نظرگرفتن توزیع رومرکز و بزرگای زمین‌لرزه­ها، میزان تغییرات پارامتر لرزه­خیزی در منطقه بین 6/1>b>8/ برآورد شد. بر اساس نتایج به‌دست‌آمده از تغییرات پارامتر لرزه‌خیزی، تغییرات اختلاف تنش حداکثری و حداقلی (σ1-σ3) در منطقه محاسبه (450-62 مگاپاسکال) گردید.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Evaluation of seismic stress change in the Makran zone

نویسندگان [English]

  • Mehrdad Mostafazadeh 1
  • Leila Mahshadnia 2
1 2 Assistant Professor, International Institude of Earthquake Engineering and Seismology(IIEES), Tehran, Iran,
2 Assistant Professor, International Institude of Earthquake Engineering and Seismology(IIEES), Tehran, Iran
چکیده [English]

The Makran zone, with a length of more than 900 km in southeastern Iran and southern Pakistan, is the only part of the Iranian plateau in which the oceanic crust of the Arabian plate with a slight slope to the north subducts beneath the continental crust of Iran. Makran is surrounded by two continental-continental zones of the Zagros and the Himalayas. Subduction of the oceanic crust along fault surfaces with a slope to the north has begun from the Early Cretaceous. Due to tectonic activity, continued subduction and the existence of a long megathrust zone in the northern part of Makran subduction and the northern shore of the Oman Sea has caused that this region has a very high risk of strong earthquakes and tsunamis. In this study, the Makran zone was evaluated by considering the concepts of seismicity parameters considered in the Gutenberg-Richter relationship. In other words, the statistical characteristic of earthquakes is considered in accordance with their spatial and temporal distribution. For this purpose, the basic data of fault and seismicity associated with the magnitude of earthquakes are investigated by the distribution of earthquakes and faults. The basis of the calculation of the b-value parameter is estimated using a frequency–magnitude distribution and correlation integral methods. Contrary to other methods, in this method, the time and space distribution of the parameters, the cumulative properties of the data and the tectonic stress level of the region associated with different earthquake seismic processes. In order to calculate these parameters, different seismic catalog (internal and external bases) have been used. Considering the distribution of earthquakes and magnitude data seismicity parameter was calculated and it is changed between 0.8<b<1.6 values. Considering the b-value quantity at any point, the map of differential stress (σ1-σ3) is calculated according to MPA (62-450 MPa).
    Based on the study of changes in seismicity parameters in the Makran zone and clustering of large earthquakes that form areas with high-stress concentration, the heterogeneity of seismicity parameters covers a significant part of the study area. Large b-values indicate the random occurrence of small earthquakes, indicating low-stress structures in parts of the region. Heterogeneity of seismic zones leads to changes in the value of b. Based on the seismicity parameters calculated in the Makran zone, the highest concentration of seismic potential for destructive earthquakes with probability is located in the southern terminal of Nehbandan, Bam, Gowk fault systems (connection zones of Nehbandan fault system terminal, Chaman, OrnachNal and Qazband with the thrust faults of Makran zone).

کلیدواژه‌ها [English]

  • Makran zone
  • seismicity
  • b-value
  • differential stress

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مجله ژئوفیزیک ایران
دوره 16، شماره 2
شهریور 1401
صفحه 191-205

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