زمین شناسی مهندسی

زمین شناسی مهندسی

تعیین ساختار زیرسطحی کم عمق زمین شناسی با استفاده از روش های ژئوفیزیکی؛ مطالعه موردی ساختگاه عباس آباد

نویسندگان
1 دانشگاه آزاد اسلامی
2 پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله
چکیده
در این مقاله دقت و کارایی روش­‌های ژئوفیزیکی لرزه‌ای با منبع فعال و غیرفعال در تعیین ساختار زمین­‌شناسی زیر سطحی یک ساختگاه منتخب در شهر عباس‌­آباد واقع در شمال ایران مورد مطالعه قرار گرفته است. دراین راستا ابتدا با حفر چندین گمانه اکتشافی ساختار زمین‌­شناسی زیرسطحی ساختگاه مورد مطالعه با استفاده از آزمایش‌های زمین‌­شناسی مهندسی تعیین گردید. نتایج نشان داد که رسوبات سطحی ساختگاه عباس‌آباد از چهار لایه زمین­‌شناسی مجزا با جنس غالب ماسه­‌ای تشکیل یافته است. سپس با حفر دو گمانه مجزای دیگر آزمایش ژئوفیزیک لرزه‌­ای با منبع فعال از نوع پایین ­چاهی به منظور تعیین دقیق پروفیل سرعت موج برشی در لایه­‌های مختلف صورت پذیرفت. در بخش بعدی با استفاده از روش ثبت آرایه­‌ای امواج خردلرزه یا میکروتریمور که یک روش ژئوفیزیک لرزه‌­ای نوین و از نوع منبع غیرفعال می‌­باشد، برای تعیین ساختار زمین‌­شناسی زیرسطحی ساختگاه مورد مطالعه در قالب پروفیل سرعت موج برشی مورد استفاده قرار گرفت. برداشت آرایه­‌ای خردلرزه­‌ه‌ا با پانزده آرایش گوناگون گیرنده‌­ها (با تعداد و فواصل مختلف گیرنده‌­ها) و با دو روش F-K و SPAC مورد تحلیل قرار گرفتند. نتایج نشان داد که هر دو روش ژئوفیزیک لرزه‌­ای با منبع فعال و غیرفعال کارایی قابل قبولی در تعیین لایه‌­بندی زمین­‌شناسی زیرسطحی ساختگاه داشته‌اند. همچین نتایج نشان داد روش پایین ­چاهی با دقت بالا سرعت موج برشی در هر لایه را نسبت به برداشت آرایه‌­ای میکروترمور تعیین می­‌کند اما نیاز به تولید مصنوعی امواج لرزه‌ای و حفر گمانه دارد. روش برداشت آرایه‌ای خردلرزه‌­ها بدون نیاز به حفاری و تولید امواج لرزه‌­ای مصنوعی کارایی بالایی هم در تعیین لایه‌­بندی زمین و هم تخمین سرعت موج برشی هر لایه داشته و به طور کلی نتایج این مقاله نشان داد که در تخمین سرعت موج برشی نسبت به روش پایین­چاهی تا حداکثر ۱۰ درصد خطا نشان می‌دهد.
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