پاسخ لرزه ای رسوبات آبرفتی ناشی از مؤلفه قائم زلزله های حوزه ی نزدیک گسل

نوع مقاله : Articles

نویسندگان

1 دانشگاه تهران/دانشکده مهندسی عکران

2 دانشگاه تهران

چکیده

یکی از راهکارهای متداول برای تعیین خصوصیات مؤلفه قائم زلزله طرح به­صورت ویژه ساختگاه استفاده از روابط تجربی نسبت طیفی شتاب قائم به افقی (V/H) است. با این ‌حال اثرات ساختگاهی تاکنون به­صورت دقیق در این روابط وارد نشده است. در این مقاله اثرات محلی ساختگاه بر روی خصوصیات مؤلفه قائم شتاب زلزله‌های میدان نزدیک بررسی شده است.  به این منظور ساختگاه­های مختلف با ویژگی­های دینامیکی متفاوت به­جای دسته‌بندی‌های کلی روابط تجربی در نظر گرفته شده و تحت تحریک مجموعه‌ای از زلزله‌های میدان نزدیک به ‌صورت دو بعدی تحلیل دینامیکی شده‌اند. نتایج به‌دست‌آمده نشان می‌دهد که نسبت طیفی شتاب قائم به افقی (V/H) از عواملی نظیر پریود اساسی ارتعاشی ساختگاه در حالت انتشار موج فشاری، نسبت پواسون خاک (υ) و همچنین مشخصات تحریک ورودی تأثیرپذیر است. مقایسه‌ی نسبت­های V/H به­دست­آمده از تحلیل‌های عددی با روابط تجربی موجود نشان می‌دهد که همخوانی نتایج در حالت اشباع بودن خاک نسبت به حالت خشک بیشتر است و با افزایش نسبت پواسون از میزان تأثیر نوع خاک بر نسبت‌های طیفی شتاب V/H کاسته می‌شود. در نهایت پیشنهاد می‌شود از معکوس امپدانس لرزه‌ای یک‌چهارم طول ‌موج بر مبنای سرعت موج فشاری، در روابط کاهندگی تجربی V/H برای لحاظ نمودن اثرات ساختگاهی استفاده شود.

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