بررسی کارآمدی مدل پوسته CRUST 1.0 برای تخمین عمق موهو در منطقه خاورمیانه

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری، گروه علوم زمین، دانشگاه آزاد اسلامی، واحد علوم و تحقیقات، تهران، ایران

2 استاد، گروه فیزیک زمین، مؤسسه ژئوفیزیک، دانشگاه تهران، تهران، ایران

3 استاد، گروه علوم زمین، دانشگاه آزاد اسلامی، واحد علوم و تحقیقات، تهران، ایران

چکیده

با توجه به پیچیدگی و تنوع ساختار‌ تکتونیکی در منطقه خاورمیانه، استفاده از روشی که بتواند عمق موهو را با بیشترین همخوانی با این ساختارها را ارائه دهد، از اهمیت ویژه‌ای برخوردار است. در این مقاله به مقایسه عمق موهو به‌دست‌آمده در منطقه خاور‌میانه با استفاده از دو شیوه متفاوت؛ 1) وارون‌سازی گرانی منشور‌های کروی، 2) تخمین عمق موهو با به‌کار‌گیری منشور‌های کروی و استفاده از مدل پوسته لرزه‌ایCRUST1.0 ، می‌پردازیم. در حالت کلی به‌دست آوردن عمق از داده‌های گرانی یک مسئله وارون غیرخطی است. در هر دو شیوه داده‌های گرانی با استفاده از روش یودا برگردان می‌شوند. با توجه به وسعت منطقه، استفاده از منشورهای کروی به‌جای منشورهای تخت در روش وارون‌سازی به‌کار رفته علاوه‌بر در نظر گرفتن انحنای زمین موجب کارآمدی روش نیز می‌شود. کمینه عمق موهوی به‌دست آمده از روش اول ۱۲ کیلومتر مربوط به بخش‌هایی از اقیانوس هند و بیشینه عمق موهو ۵۴ کیلومتر مربوط به قسمت‌های غربی فلات تبت است که با مرز صفحات و ساختارهای تکتونیکی همبسته است. محدوده عمق موهو در روش دوم در بازه‌ ۵/۷ تا ۴۹ کیلومتر است که مقدار کمینه مربوط به بخش‌هایی از اقیانوس هند و مقدار بیشینه مربوط به قسمت‌هایی از زاگرس است. مقایسه نتایج دو روش نشان می‌دهد که نتایج حاصل از روش اول به‌دلیل وارون‌سازی داده‌های گرانی‌سنجی نسبت به روش دوم که از مدل پوسته لرزه‌ای CRUST 1.0 برای تخمین عمق موهو استفاده کرده، کاملاً با مرز صفحات همخوانی داشته و کلیه ساختار‌های تکتونیکی منطقه را نشان‌ می‌دهد.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Evaluating CRUST1.0 crustal model efficiency for Moho depth estimation in Middle East region

نویسندگان [English]

  • Parastoo Jalooli 1
  • Hamid Reza Siahkoohi 2
  • Hossein Zomorrodian 3
1 Ph.D. Student, Department of Earth Sciences, Islamic Azad University, Science and Research Branch, Tehran, Iran
2 Professor, Department of Earth Physics, Institute of Geophysics, University of Tehran, Tehran, Iran
3 Professor, Department of Earth Sciences, Islamic Azad University, Science and Research Branch, Tehran, Iran
چکیده [English]

Study of Moho in Middle East and surrounding region is of great importance for scientists, because it has a rich geological history and contains parts of the Eurasian, Indian, African and Arabian plates as the main plates and some small plates. According to complexity and different tectonic structures in Middle East using a proper method that yields a Moho depth model which is in accordance with these structures, has a great importance. In this paper we compare the Moho depth obtained from two different methods, 1) Gravity data inversion of spherical prisms (tesseroids) and 2) Moho depth evaluation using tesseroids and CRUST1.0 crustal model. Determining of Moho depth from gravity data is a nonlinear inverse problem. Regarding the extent of the study area we use an efficient inversion method (Uieda’s inversion method) in order to consider the earth's curvature by using spherical prisms instead of rectangular prisms. In this method one needs to minimize the  cost function, where is the fidelity term,  is the penalty term and  is regularization parameter. In this method in addition to Moho depth, we need to estimate three hyper parameters namely the regularization parameter ( ), Moho reference level ( ) and density contrast ( ). They are estimated in two steps during the inversion by holdout-cross validation methods.To estimate the relief of the Moho from gravity data, first one must obtain the gravitational effect of the target anomalous density distribution attributed to the Moho relief, this requires eliminating all gravity effects other than that of the target anomalous density from observed data. In the first method tesseroid modeling is used to calculate the gravity effect of the topography and sediments. The effect of topography and crustal sediments are removed using global topography and crustal models. In the second method first we extract Moho depth over the study region from CRUST1.0 model and then evaluate gravity effect arising from this anomalous Moho, then using inversion method to estimate the Moho depth from CRUST 1.0 model. According to the results, the minimum depth of Moho is about 12 km in some parts of Indian Ocean and the maximum depth is about 54 km in the west of Tibetan plateau from the first method which is in accordance with plate boundaries and correlates well with the prominent tectonic features of the Middle East region. The Moho depth obtained from the second method varies between 7.5 and 49 km where the minimum depth is related to the parts of Indian Ocean and maximum depth is appeared in parts of the Zagros in Iran. Comparing the results of two methods demonstrates the acceptable performance of the adapted inversion procedure and utilization of spherical prisms but the calculated Moho depth from second method failed to estimate acceptable Moho depth especially in divergent boundary at Red sea, Gulf of Aden and Indian Ocean. The results indicate that the CRUST1.0 model, at least over an area with large extent, is not a suitable model for gravity inversion and Moho depth estimation.

کلیدواژه‌ها [English]

  • Moho depth
  • spherical prisms
  • gravity data inversion
  • CRUST1.0 crustal model

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فیزیک زمین و فضا
دوره 48، شماره 1
تاریخ انتشار الکترونیکی: 19 اردیبهشت 1401
اردیبهشت 1401
صفحه 1-11

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