بررسی اثر ساختگاه در حاشیه حوزه رسوبی از طریق پردازش های میکروترمور و تحلیل عددی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه مهندسی عمران، واحد علوم و تحقیقات تهران، دانشگاه آزاد اسلامی، تهران، ایران

2 پژوهشکده مهندسی ژئوتکنیک، پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله، تهران، ایران

3 گروه مهندسی عمران، دانشگاه ارومیه، ارومیه، ایران

چکیده

علیرغم کارهای گسترده ای که در زمینه پردازش های میکروترمور و آنالیز نسبت طیفی مولفه افقی به قائم(H/V) انجام یافته است در مطالعات محدودی تلاش شده است که این مشاهدات و نتایج تجربی از طریق مدلسازی­های عددی 2 و3 بعدی تفسیر و توجیه گردد که این موضوع در مقاله حاضر  با انتخاب حوضه رسوبی  شهر ارومیه مورد بررسی واقع گردیده است. مطالعات قبلی ریز­پهنه­بندی لرزه­ای در این شهر نشان دهنده قله­های نسبت طیفی H/V  پهن یا  دوقله­ نزدیک به هم در نقاطی از حاشیه حوضه رسوبی است. با بررسی توابع تبدیل حاصل از تحلیل­های عددی یک و دوبعدی انجام یافته روی یک مقطع  شرقی-غربی از حوضه رسوبی در این شهر مشخص گردید که این مساله می تواند ناشی از تغییر ناگهانی ضخامت آبرفت و تداخل موج­های برشی دو محیط مختلف در طرفین نقطه اندازه­گیری شده و بیانگر وجود شرایط دوبعدی باشد. در این بررسی همخوانی بسیار مناسبی بین موقعیت دو قله تلفیق شده در منحنی H/V  و منحنی تابع انتقال حاصل از تحلیل عددی دو بعدی بدست آمد. در این مطالعه نشان داده شد که فرکانس­های غالب در شرایطی که اثرات دوبعدی حاکم باشد نسبت به شرایط یک بعدی به سمت فرکانس­های بالاتر جابجا می­گردد. همچنین این مطالعه پیشنهاد می کند که در تفسیر منحنی­های H/V  جهت تشخیص قله­های واقعی مرتبط با اثر ساختگاه، روند تغییرات فرکانس­های غالب  منطقه مورد توجه قرار گیرد و هر منحنی بصورت منفرد ارزیابی نگردد.

کلیدواژه‌ها


عنوان مقاله [English]

Site Effect Evaluation in Basin Edge Using Microtremor Data and Numerical Modeling

نویسندگان [English]

  • Mahdi Kouklanifar 1
  • Ebrahim Haghshenas 2
  • Mohsen Kamalian 2
  • Hadi Bahadori 3
1 Science and Research Branch, Islamic Azad University, Tehran, Iran
2 Geotechnical Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
3 Urmia University, Urmia, Iran
چکیده [English]

Despite extensive studies on the microtremor processing technics and horizontal to vertical (H/V) spectral ratio analysis, limited studies have been tried to interpret the observations and experimental results and confirming them via two and three-dimensional numerical modeling. The present article deals with this issue by selecting the Urmia alluvial basin. Previous seismic microzonation studies in this city show a broad peak or two neighboring peaks, close to each other at some points near to the edge of sedimentary basin. By examining the transfer functions obtained from one-dimensional and two-dimensional numerical analysis performed on an east-west section of the Urmia sedimentary basin, it was found that this issue could be due to a sudden change in thickness of the soil profiles on either side of measuring point and coupling of shear waves passing through these two different environments. This study shows a very good agreement between the frequency position of the two neighboring peaks between the H/V curve and two-dimensional transfer function. In addition, this study shows that when two-dimensional site effect is predominant, the resonance frequencies are higher compared to one-dimensional conditions. This study also suggests that for recognition of the real peaks in H/V curves, the variation trend of dominant frequencies between the different measuring points in study area should be considered and each curve should not be evaluated individually.

کلیدواژه‌ها [English]

  • Microtremor
  • Two and Three-Dimensional Site Effects
  • Alluvial Basin Edge
  • Shear Waves Coupling
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