مقایسه سازوکارهای گسله‌های فعال در ترانشه‌های دیرینه لرزه‌شناسی و سازوکارهای کانونی در جنوب البرز مرکزی

نوع مقاله: مقاله تحقیقی‌ (پژوهشی‌)

نویسنده

دانشیار، پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله، تهران، ایران

10.30499/ijg.2020.106199

چکیده

صفحه­های گسلی از سه ترانشه (مطالعات دیرینه‌ لرزه­شناسی) با سن­های پلایستوسن جوان و هولوسن با سازوکارهای کانونی مقایسه شده‌اند تا ارتباط میان این دو داده مشخص شود. نشان داده شدکه ارتباط مستقیم میان داده­های سطحی (گسله­ها و خش‌خط آنها) و داده­های عمقی (سازوکار کانونی) وجود دارد. تانسور تنش با اندازه‌گیری­های سطحی از سه ترانشه راندگی شمال تهران، مشا و فیروزکوه به­دست­آمد. از تانسور تنش محاسبه­شده، صفحه­های گسلی‌ای انتخاب شدند که با روند عمومی گسله­های مشا و فیروزکوه همسو هستند. این داده با سازوکارهای کانونی همخوانی خوبی دارد. در ترانشه سوم که داده­ها برای حل تانسور تنش کافی نیستند، با تعیین اندازه میانگین روند، شیب و شیب خش‌خط­ها (ریک)، در جایی که آرامش لرزه‌ای برقرار است سازوکار کانونی دیرینه پیشنهاد شد. براساس یافته­های سطحی و سازوکارهای کانونی، بیشینه تنش افقی (5±45~N1s) و تنش کمینه (3s) شیب نزدیک به افق دارند و محور تنش میانی (2s) عمود بر زمین با رژیم زمین‌ساختی راستالغز است.
    گسله مشا با روند (E100N) و شیب به سوی شمال، سازوکار راستالغز چپ‌بر و یک مؤلفه کوچک کششی دارد که در پایانه خاوری خود به گسله فیروزکوه با روند (E60N) و شیب به سوی جنوب با سازوکار راستالغز همراه با یک مؤلفه فشاری می­پیوندد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Comparison of surface slip-data deduced from paleoseismological sites and focal mechanisms in the South Central Alborz

نویسنده [English]

  • mohammadreza Abbassi
Associate Professor, International Institute of Earthquake Engineering and Seismology, Tehran, Iran
چکیده [English]

Focal mechanism and surface slip data are used to investigate the relationship between kinematic studies conducted on young geological units, especially in trenches of paleoseismolical sites, Late Pleistocene and Holocene in age. It has shown that there is direct relationship between data obtained on surface and seismic data in depth. Kinematic measurements in three trenches for paleoseismological sites on North Tehran Thrust, Mosha fault and Firuzkuh fault are used to calculate the stress tensor. Stress tensors and their associated fault planes and focal mechanism data are compared. Fault planes obtained from calculated stress tensors whose fault planes lie parallel or close to the general trends of Mosha and Firuzkuh faults are in good agreement with focal mechanism. The third trench on North Tehran Thrust displayed insufficient data to obtain an appropriate stress tensor, however the average of strikes, dips and rakes allow to propose a paleofocal mechanism for an area of seismic quiescence. Based on fault plane inversion and focal mechanisms, overall, maximum (σ1~N045±5) and minimum (σ3) principal stresses are subhorizontal and the intermediate principle stress (σ2) is vertically oriented. This is consistent with a dominant strike-slip regime.
The Mosha fault (trending N100E, dipping to North) is a left-lateral strike-slip fault with a minor extensional component and joins Firuzkuh fault (trending N60E, dipping to South) as strike-slip fault with a compressional component.

کلیدواژه‌ها [English]

  • Central Alborz
  • Tehran
  • contemporary stress
  • Active fault
  • tectonic regime
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