تغییرات میدان تنش در منطقه گذار بین زاگرس و مکران با استفاده از وارون‌سازی سازوکار کانونی زمین‌لرزه‌ها

نوع مقاله : مقاله تحقیقی‌ (پژوهشی‌)

نویسنده

استادیار پژوهشگاه بین‌المللی زلزله‌شناسی و مهندسی زلزله، تهران، ایران

10.30499/ijg.2020.221729.1253

چکیده

 وارون‌سازی تانسور تنش با استفاده از سازوکار کانونی زمین‌لرزه­ها یکی از روش­های مورد استفاده در مطالعه تنش­های زمین‌ساختی است. در این مطالعه با استفاده از این روش، راستای تنش بیشینه افقی در منطقه گذار بین زاگرس و مکران تعیین شده است. نتایج، نشان­دهنده تغییرات زیاد در راستای محورهای اصلی تنش در این منطقه است. در اطراف تنگه هرمز، محورهای تنش افقی بیشینه می­چرخند و الگوی پیچیده‌ای را نشان می­دهند. این چرخش در سمت راست خط عمان، به‌صورت ساعت‌گرد از باختر به خاور حول این خط فرضی اتفاق می­افتد، اما در سمت دیگر، به‌خصوص جایی که جزیره قشم قرار دارد، جهت‌گیری­های متقاطع تنش افقی بیشینه نشان­دهنده پیچیدگی میدان تنش است. احتمال دارد که تفاوت خصوصیات پوسته اقیانوسی و قاره‌ای مسئول تفاوت در جهت‌گیری‌های میدان تنش در این منطقه باشد. راستاهای تنش بیشینه افقی با توجه به روند امتداد گسل­های فعال منطقه، به‌خوبی با سازوکار گسلش در مناطق مورد مطالعه همخوانی دارد. دیگر روش­های ژئوفیزیکی نیز چرخش مشابهی را در اطراف تنگه هرمز به نمایش می­گذارند و این راستاها با اطلاعات حاصل از آنها سازگارند. این مطالعه می­تواند با فراهم کردن نگرشی نو، به درک ساختار و فرایندهای زمین‌ساختی در این منطقه پیچیده کمک کند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Stress field variations in the Zagros-Makran transition zone by using earthquake focal mechanism stress tensor inversion

نویسنده [English]

  • Shahrokh Pourbeyranvand
Assistant Professor, International Institute of Earthquake Engineering and Seismology Tehran, Iran
چکیده [English]

Knowing about stress variations in the Zagros and Makran transition zone in the southwest of Iran is necessary to study the deformation resulting from the oblique collision between the Eurasian and the Arabian plates and gain insight into the complicated tectonics of this crucial region. The stress tensor inversion of earthquake focal mechanisms is one of the methods used to study tectonic stresses. In this study, the direction of maximum horizontal stress in the transition zone between the Zagros and Makran was obtained using this method. The results indicate significant changes in the principal axes of stress in this region and show the stress field's complicated pattern. The rotation in the right of the Oman Line takes place in a clockwise manner from west to east around this imaginary line. Still, on the other side, especially where Qeshm Island is located, the opposing direction of the maximum horizontal stress directions indicates the stress field's complexity. The axis of maximum horizontal stress in this region is compared with the single earthquake focal mechanism's P axis. Since almost all earthquake faulting mechanisms are of reverse and strike-slip type, the comparison shows a good agreement between the resulting directions. The maximum horizontal stress directions are also investigated concerning the trend of the active faults consistent with the fault mechanism in the studied areas. Focal mechanism data were used to obtain information on the state of stress in 5 subdivisions of the data, including teleseismic and local events in the Zagros region. The investigation shows acceptable agreement between the observed faulting mechanisms and what can be predicted based on the fault plane orientations and stress directions in the area. These alignments also correlate with the data from other geophysical methods that exhibit a similar rotation around the Strait of Hormuz. The plate motion velocity vectors were estimated using the NOVEL-1A model. On the right side of the Oman Line in the SE Zagros, the stress and plate motion directions are similar, while in the western part of the Zagros, they differ by about 35 degrees. This angular difference between the stress and plate motion velocity vectors is obverse between the Qeshm Island and the area in the Strait of Hormuz's left-hand side in the Zagros. The oceanic and continental crust differences in the area may be responsible for the variation of these directions in the region. By providing a new perspective, this study can help in understanding the tectonic structure and processes in this complex region.

کلیدواژه‌ها [English]

  • focal mechanism
  • Inversion
  • Makran
  • Stress
  • Tectonic
  • transition zone
  • Zagros
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