ارائه الگوی لرزه زمین ساختی بر اساس مطالعۀ تطبیقی توزیع تنش کولمب با پارامترهای لرزه‌ای در زوج زمین‌لرزه اهر-ورزقان

نوع مقاله : سایر مقالات

نویسندگان

1 استادیار، دانشگاه پیام نور بیرجند، بیرجند، ایران

2 دانشجوی کارشناسی ارشد، دانشگاه پیام نور مرکز تهران شرق،تهران، ایران

10.22044/jrag.2020.8870.1263

چکیده

زوج‌ زمین‌لرزه اهر- ورزقان به صورت دو رخداد پیاپی در فاصلۀ زمانی و مکانی نسبتا کوتاهی از هم، در تاریخ 21 مرداد ماه 1391 (11 آگوست 2012) باعث ایجادگسیختگی سطحی بطول 12 کیلومتر و لرزش مناطقی شد که قبلا هیچ گسل فعالی در آن شناسایی نشده بود. با توجه به نظریۀ انتقال تنش و احتمال متأثر بودن رخداد دوم از رخداد اول، تغییرات تنش کولمب برای وضعیت‌های هندسی مختلف از صفحات گرهی دو رخداد مورد بررسی قرار گرفت و با توزیع مکانی پس‌لرزه‌ها مطابقت داده شد. با بررسی الگوی توزیع تنش کولمب در محیط اطراف و در نظر گرفتن پدیده برهم کنش، مشخصات °82، °89 و °164 برای امتداد، شیب و ریک گسل مسبب رخداد اول با سازوکار راست لغز و °7، °49 و °31 برای امتداد، شیب و ریک گسل مسبب رخداد دوم با سازوکار معکوس همراه با مؤلفۀ کوچک امتداد لغز در نظر گرفته شد. نتایج بدست آمده از الگوی توزیع تنش مطابقت زیادی با نقشه‌های تغییرات مکانی مقدار b (b-value) در داده‌های قبل از زلزله دارد. پارامترb در واقع شیب رابطۀ گوتنبرگ-ریشتر است که مرتبط با ساختار زمین ساختی منطقه بوده و وابسته به تنش موجود در منطقه می‌باشد. با توجه به منطقۀ حداقل مقدار b در داده‌های قبل از زلزله، الگوهای توزیع تنش کولمب برای گسل‌های منشاء، گیرنده و گسل‌های با جهت بهینه، نحوه انتشار گسیختگی نسبت به کانون رخداد اول و تظاهر سطحی آن و نیز سازوکار مختلف قطعات سیستم گسلی، ساختار خم فشارشی در حال توسعه برای منطقه متأثر از زوج زمین‌لرزه اهر-ورزقان پیشنهاد می‌گردد. این مدل ساختاری پیشنهادی می‌تواند به ارزیابی خطر لرزه‌ای در مناطق محتمل برای شکستگی‌های آتی کمک کند.

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