تعیین فرکانس غالب و طبقه‌بندی ساختگاه در تعدادی از ایستگاه‌های شتابنگاری شمال‌غرب ایران، با استفاده از اندازه‌گیری میکروتریمورها

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشگاه شهید مدنی آذربایجان، تبریز، ایران

2 پژوهشگر، دانشگاه گیفو، ژاپن

چکیده

در این مطالعه با استفاده از اندازه‌گیری میکروتریمورها در 15 ایستگاه شتابنگاری در شمال‌غرب کشور، فرکانس غالب تعیین شده و بر اساس آن طبقه‌بندی ساختگاه انجام گرفته است. برای این منظور اندازه‌گیری‌ها به مدت 20 شبانه روز انجام گرفتند. پس از تصحیح داده‌های خام، نسبت طیفی مولفه‌ی افقی به مولفه‌ی قائم محاسبه شده و فرکانس متناظر با دامنه‌ی حداکثر به عنوان فرکانس غالب ساختگاه لحاظ گردید. همچنین در 11 ایستگاه با کیفیت مناسب میکروتریمورها، نسبت‌های طیفی میکروتریمورها و رکوردهای زلزله‌ی ثبت شده در ایستگاه‌های شتابنگاری مقایسه شده‌اند. انطباق این دو نسبت طیفی رضایت بخش ارزیابی می‌شود. بر اساس تحلیل میکروتریمورها، حداقل و حداکثر فرکانس به ازای ساختگاه‌های مختلف به ترتیب برابر 72/1 و 34/7 هرتز حاصل شده‌اند. در این مطالعه همچنین با استفاده از مطالعات گذشته، سرعت موج برشی در 30 متر بالایی تعیین و به کمک آیین‌نامه‌های مختلف، نوع خاک ساختگاه‌ها طبقه‌بندی شده‌اند. اگر تقسیم بندی بر اساس فرکانس غالب ساختگاه با تقسیم بندی بر اساس سرعت موج برشی در 30 متر بالایی گزارش شده توسط مرکز تحقیقات راه، مسکن و شهرسازی مقایسه شود، اختلافات قابل توجهی مشاهده می‌شود. این اختلاف می‌تواند ناشی از عدم قطعیت در سرعت موج برشی گزارش شده و هم در فرکانس غالب تخمین زده شده باشد.

کلیدواژه‌ها


عنوان مقاله [English]

Determination of Dominant Frequency and Site Classification Using Microtremor Measurements for Some Strong Motion Stations in North-Western Iran

نویسندگان [English]

  • Abdolhossein Fallahi 1
  • Meghdad Samaei 2
  • Jafar Karashi 1
1 Shahid Madani University, Tabriz, Iran
2 Researcher, Gifu University, Japan.
چکیده [English]

In the current study, using microtremor measurements at 15 stations of strong ground motion network in North-western Iran, dominant frequency is determined and sites are categorized. After correction of raw data, horizontal to vertical spectral ratio is calculated and the frequency corresponding to the greatest amplitude is acknowledged as the dominant frequency. Also at 11 stations with good quality of recorded microtremors, horizontal to vertical ratio of earthquake motion is calculated. Agreement between these two spectral ratios is quite satisfactory. Maximum and minimum observed dominant frequencies are 1.72 and 7.34 respectively. Correspondingly, using past studies, shear wave at the top 30 m ( ) is estimated and based on different seismic codes, sites are categorized. If the categorization based on predominant frequency is compared with categorization based on reported by building and housing research center, dramatic differences will be observed. These differences could be attributed to uncertainties in reported Vs30 as well as estimated dominant frequencies.

کلیدواژه‌ها [English]

  • microtremors
  • Strong Motion Station
  • dominant frequency
  • Natural Period
  • Site Classification

کتابنگاری

مرکز تحقیقات راه، مسکن و شهرسازی، 1393- آیین‌نامه طراحی ساختمان‌ها در برابر زلزله (استاندارد 2800)، ویرایش چهارم، 19 ص.

 

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