مجله ژئوفیزیک ایران

مجله ژئوفیزیک ایران

مطالعه زمین‌ساخت فعال البرز (ایران) با استفاده از داده‌های ژئودتیکی

نوع مقاله : مقاله پژوهشی‌

نویسندگان
1 دانشجوی دکتری ژئوفیزیک، دانشکده علوم زمین، دانشگاه تحصیلات تکمیلی علوم پایه زنجان، زنجان، ایران
2 دانشیار، دانشکده علوم زمین، دانشگاه تحصیلات تکمیلی علوم پایه زنجان، زنجان، ایران
3 استادیار، دانشکده مهندسی، دانشگاه زنجان، زنجان، ایران
4 استاد، دانشکده علوم زمین، دانشگاه تحصیلات تکمیلی علوم پایه زنجان، زنجان، ایران
چکیده
در این پژوهش آهنگ تغییرشکل البرز با استفاده از تلفیق داده‌های شبکه‌های جدید جی‌پی‌اس دائمی موقعیت‌یابی یکپارچه مالکیت‌ها (شمیم) و شهرداری تهران (سمت) و شبکه جدید موقت IASBS_NCC با داده‌های ایستگاه‌های دائمی و موقت سازمان نقشه‌برداری کشور بررسی شده است. افزایش تعداد ایستگاه‌ها باعث بهبود میدان سرعت‌ شده است که نشان می‌دهد مسبب تغییرشکل فعال در تمام عرض البرز، چندین گسله فعال است. برخلاف باور غالب درباره تقسیم کرنش در البرز بین گسله‌های امتدادلغز در پهلوی جنوبی و گسله فشارشی خزر در پهلوی شمالی، میدان سرعت جدید نشان­دهنده پخش بودن حرکات امتدادلغز و فشارشی در طول گسله‌های مختلف در عرض البرز است. در مطالعات پیشین به علت نبود ایستگاه‌ بین گسله خزر و دیگر گسله‌های دامنه شمالی، تمام تغییرشکل مشاهده‌شده در نیمه شمالی البرز به گسله خزر مرتبط دانسته شده است. در میدان سرعت جدید، وجود یک بردار جی‌پی‌اس جدید بین گسله‌های شمال البرز و خزر در قسمت شرقی البرز بر نقش غالب گسله شمال البرز در جایدهی کرنش دلالت دارد. نقشه جدید همانند نقشه‌های قبلی، مقدار کرنش کلی کمتری برای غرب البرز نشان می‌دهد که در همخوانی با سطح لرزه‌خیزی کمتر مشاهده­شده در این منطقه است. میدان سرعت جدید نشان­دهنده وجود سامانه کششی فعال در غرب البرز در بازه طول جغرافیایی ۴۹ تا ۵/۵۰ درجه است و همچنین نشان­دهنده حرکت امتدادلغز دو میلی‌متری در لبه شمالی ایران مرکزی است که می‌تواند با پهنه گسلی آران- طرود و گسله عطاری مرتبط باشد. با وجود اینکه مطالعات زلزله‌نگاری دال بر فعالیت بیشتر نیمه شرقی گسله مشا است و مطالعات زمین‌شناسی، آهنگ تغییرشکل آن را دو میلی‌متر بر سال برآورد کرده است، میزان هر دو حرکت امتدادلغز و فشارشی در طول گسله مشا کمتر از یک میلی‌متر بر سال است. در محدوده کلان‌شهر تهران، میزان حرکت امتدادلغز و فشارشی چشمگیر نیست و در حد کمتر از یک میلی‌متر است که به معنای دوره بازگشت بسیار طولانی زلزله‌های بزرگ است.
کلیدواژه‌ها

عنوان مقاله English

Constraint on the active tectonics of the Alborz (Iran) using geodetic data

نویسندگان English

Mohammad Javad Banimahdi Dehkordi 1
Zahra Mousavi 2
Esmaeil Shabanian 2
Madjid Abbasi 3
Abdolreza Ghods 4
1 Ph.D. Student, Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran
2 Associate Professor, Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran
3 Assistant Professor, Department of Surveying (Geomatics) Engineering, Faculty of Engineering, University of Zanjan, Iran
4 Professor, Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran
چکیده English

In this research, the deformation pattern of Alborz is investigated using a combination of data from the new permanent GPS networks that belong to State Organization for Registration of Deeds and Properties (SHAMIM) and Tehran Municipality (SAMT), the new temporary IASBS_NCC network and the permanent and temporary stations of the National Cartographic Organization. The addition of the 27 new GPS stations has improved the obtained velocity field, which shows that the active deformation happens across the entire width of Alborz from south to north by several faults and active fault zones. Contrary to the common belief about the strain partitioning in the Alborz Mountains between the strike-slip faults in the southern flank of the Alborz and along the compressional south-dipping Khazar fault in the northern flank of the Alborz, the new velocity field indicates a spread of strike-slip and compressional movements along different faults across the width of the Alborz. In previous works, due to the lack of GPS stations between the Khazar fault and other active faults in the northern flank of the Alborz (e.g. North Alborz fault), all the observed deformation in the northern flank of the Alborz has been associated with the Khazar fault. In the improved velocity field, the presence of a new GPS vector between the North Alborz and the Khazar fault in the eastern part of the Alborz indicates a dominant role of the North Alborz fault in the strain accommodation once compared to the Khazar fault. Like the previous works, the new velocity field shows a lower total strain for the western Alborz, which is consistent with the lower observed seismicity in the western Alborz. The new velocity field indicates an active extensional system in the western Alborz in a longitude range of 49o to 50.5o around the Tarom Valley. The extensional system might be related to the counterclock wise rotation of the South Caspian Basin relative to Eurasia. The improved velocity field shows a noticeable strike-slip motion of 2 mm/yr at the northern edge of Central Iran which could be related to the Aran-Torud fault zone and Attari fault. There is also a shortening rate of ~2 mm/yr between the northern edge of Central Iran and the Eastern Alborz which could be related to the salt tectonic within the Great Kavir fault. The improved velocity field shows a right-lateral strike-slip motion of ~1 mm/yr across the Indes and Kushk-Nosrat faults. Despite the observed large seismic activity and a geological slip rate of 2 mm/yr for the eastern part of the Mosha fault, both strike-slip and compressional slip rates along the Mosha fault are less than 1 mm/yr. Within a radius of ~50 km from the center of Tehran metropolitan area, there is no noticeable rate of strike-slip or compressional movement and the strain rate is around the error limit or less than 1 mm/yr. The low strain rate implies a very long earthquake return period for large earthquakes in Tehran metropolitan area.

کلیدواژه‌ها English

Alborz
GPS
hazard analysis
Tehran
velocity field
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