توموگرافی امواج سطحی برای منطقه فرورانش مکران

نوع مقاله : مقاله پژوهشی‌

نویسندگان

1 دانشجوی دکتری، دانشکده علوم زمین، دانشگاه تحصیلات تکمیلی علوم پایه زنجان ، زنجان، ایران

2 دانشیار، دانشکده علوم زمین، دانشگاه تحصیلات تکمیلی علوم پایه زنجان ، زنجان، ایران

چکیده

در این مطالعه سعی شده است با استفاده از توموگرافی امواج سطحی و برگردان منحنی­های پاشش، مدل سه­بعدی ساختار سرعتی موج برشی برای منطقه فرورانش مکران تعیین و با استفاده از نتایج آن، به سؤالاتی درباره زمین‌ساخت منطقه و هندسه صفحه فرورونده پاسخ داده شود. برای این پژوهش از داده­های ثبت­شده در 58 ایستگاه لرزه­نگاری در منطقه مکران در فاصله زمانی 6/2016 تا 5/2019 استفاده شده و روش توموگرافی با فرض دو جبهه موج تخت برای توموگرافی موج سطحی به‌کاررفته­است. توموگرافی برای سرعت فاز در نه دوره تناوب بین 25 تا 125 ثانیه انجام شده و با وارون­سازی منحنی­های پاشش، مدل سه­بعدی سرعت موج برشی برای منطقه مورد مطالعه به‌دست­آمده­است. نتایج نشان می­دهد در بخش غربی مکران و در شمال تنگه هرمز، سنگ‌کره عربی به زیر ناحیه سنندج- سیرجان و کمان ماگمایی ارومیه- دختر رانده شده است. همچنین در بخش میانی منطقه (در مکران غربی و زیر گودال جازموریان) یک سنگ‌کره اقیانوسی تخت وجود دارد که احتمالاً باقی­مانده ورقه اقیانوسی فرورونده‌ای است که از این ورقه جدا شده و باقی مانده است. همچنین در شرق منطقه، یک سنگ‌کره اقیانوسی دیده می­شود که با شیب کم تا شمال گودال جازموریان امتداد دارد و سپس در زیر کمان آتشفشانی با شیب زیاد فرورانش می­کند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Surface wave tomography of the Makran subduction zone

نویسندگان [English]

  • Reza Zeynoddini Meymand 1
  • Khalil Motaghi 2
  • Esmail Shabnian 2
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
چکیده [English]

This study presents a 3-D model of the shear wave velocity (Vs) for SE Iran, containing the Makran subduction zone and termination of the Zagros collision zone. The model is developed using surface wave tomography and the associated local dispersion curves that were inverted to the Vs velocity maps. Our findings provide insights into the tectonics of the SE Iran region and the geometry of the subducting lithosphere. To obtain Rayleigh waveforms, we extracted data from 458 teleseismic earthquakes recorded by 58 seismic stations in the Makran region between June 2016 and May 2019. Events with magnitudes greater than 5.5, epicentral distances between 30º and 120º, and depths shallower than 50 km were considered for two-plane wave tomography. This resulted in phase velocity maps at nine periods ranging between 25 s and 125 s. Our results suggest the presence of a high-velocity anomaly at the northern coast of the Gulf of Oman extending ~100 km northward up to the Qasr-e Qand fault and the southern edge of the Jaz Murian depression as it was observed at shorter periods of 25-40 s. Further west of Makran and north of the Strait of Hormuz, there is also a high-velocity anomaly at the southwest of the Zendan-Minab-Palami fault at periods of 25-40 s. At periods of 50-125 s, this anomaly is observed at the northern latitudes beneath the Sanandaj-Sirjan zone at the termination of the Zagros collision zone. Our analysis suggests that this anomaly reveals underthrusting of the Arabian lithosphere under Sanandaj-Sirjan zone and Urumieh-Dokhtar magmatic arc. Additionally, we detected a low-velocity anomaly at periods of 25-33 s showing a crustal root potentially generated by underthrusting of the Arabian lithosphere in this region. At the second inversion step, we employed a nonlinear inversion of the local dispersion curves to construct a 3-D Vs model. Our results indicate that there is a flat
high-velocity anomaly in the middle of the study region (in the western Makran and under the depression of Jaz Murian), indicating a horizontal oceanic lithosphere, potentially remaining from a truncated oceanic lithosphere between the collision and subduction zones. Furthermore, our findings suggest the presence of a near-horizontal oceanic lithosphere in the eastern part of the study area, extending at a low angle underneath the northern edge of the Jaz Murian depression and subsequently subducting beneath the volcanic arc with a steep angle. Finally, we identified a low Vs anomaly at the crustal-scale in the Sistan suture zone, which stretches towards the north-northwest and is limited by the large N-S directed strike-slip faults.
 

کلیدواژه‌ها [English]

  • Makran
  • subduction
  • surface wave tomography
  • oceanic lithosphere
  • magmatic arc
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