İstanbul deprem istasyonlarında alınan deprem ve mikrotremor kayıtlarının analizi
Başlık çevirisi mevcut değil.
- Tez No: 55761
- Danışmanlar: PROF.DR. ATİLLA ANSAL
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 74
Özet
ÖZET Depremler sırasında yapılarda görülen hasar üzerinde yapısal özelliklerin yanı sıra deprem kaynak ve dalga yayılma yolu özellikleri ile yerel zemin tabakalarının dinamik davranış özelliklerinin önemli etkisi bulunmaktadır. Bu yüzden, yapıların depreme dayanıklı olarak projelendirilmesinde oturtulacakları zemin tabakalarının başta hakim peryotlar olmak üzere dinamik özelliklerinin belirlenmesi büyük önem taşımaktadır. Yerel zemin tabakalarının dinamik davranış özelliklerinin belirlenmesinde kullanılan üç temel yaklaşım bulunmaktadır. Bunlardan ilki, yerel zemin tabakalarının depremler sırasında gösterdikleri davranış özelliklerinin gerçek deprem kayıtlarının analiz edilmesi ile belirlenmesi olup, bu yaklaşımın sınırlayıcı yönü, sismik açıdan fazla aktif olmayan yerlerde analiz için gerekli sayıda deprem kaydının alınmasının uzun zaman alabilmesidir. İkinci ve en fazla kullanılan yöntem, zemin tabakalarının dinamik özelliklerinin arazi ve laboratuvar deneyleri ile belirlenmesidir. Arazi ve laboratuvar deneylerinin maliyetlerinin yüksek oluşu bu yöntemin geniş bölgelerin analizinde kullanımım zorlaştırmaktadır. Diğer bir alternatif yöntem, ilgilenilen bölgede kaydedilen mikrotremorların analiz edilerek yerel zemin tabakalarının dinamik davranışları hakkında bilgi edinilmesidir. Mikrotremor verilerinin kaydedilmesi ve analizleri diğer yöntemlerle karşılaştırıldığında oldukça basit ve ekonomik olmaktadır. Ayrıca kayıt ve analiz için ihtiyaç duyulan süre de kısadır. Bu yönüyle mikrotremorlar, deprem mühendislerine geniş olanaklar sunmaktadır. Bu çalışma kapsamında, İstanbul'da kurulu bulunan deprem istasyonları tarafından kaydedilen depremlerin ivme, hız ve yerdeğiştirme tepki spektrumlan elde edilmiş ve istayonlann bazılarında mikrotremor hız kayıtlan alınmıştır. Deprem kayıtlarının tepki spektrumlarında görülen zemin hakim peryotlar ile mikrotremor kayıtlarının Fourier spektrumlarında ortaya çıkan hakim peryot değerleri karşılaştırılmış ve aralarda oldukça iyi uyum olduğu görülmüştür xı
Özet (Çeviri)
station were compared, it was seen that similar predominant periods appeared at these two spectra. When new settlements are planned or the potential earthquake site response of different regions that have been already settled wanted to be determined, microzoning studies have to be carried out. Especially for the crowded cities such as Istanbul, microzrination maps have to be prepared immediately. As the area of the city is very large, it will be very difficult to achieve an adequate microzoning study by means of in - situ or laboratory tests. In this study, it was shown that the earthquake response characteristics of the local soil layers could be successfully estimated by the use of microtremor data. As the time and money required for recording and analysis of microtremor data are low, microtremors seem to be an appropriate way for determining the earthquake response characteristics of soil layers. From the engineering point of view, microtremors offer very attractive advantages to the geotechnical engineers who need to have knowledge about the dynamic characteristics of the soil layer especially for microzoning studies. It is believed that, in Istanbul a microzonation study based on microtremor data will be very usefull for engineering purposes. As the cost of the operation and time required to get results are low relatively, using the microtremor Fourier spectra for determining the predominant periods of the local soil layers or using the microtremor spectral ratios for determinig the relative amplification ratios seem to be the best way for the cities such as Istanbul. xviMexico earthquake (M=8). In this event, despite of epicentral distance of several hundred kilometers, the ~2 sec fundamental vibration mode of the Mexico City lake- bed zone was reached and severe structural damages that led to thousands of casualties was caused due to the resonance. When the natural period of the structures are equal to the predominant periods of soil layers, than double resonance occurs. The spectral analysis is widely used in determining the characteristics of earthquake ground motions. In spectral analysis, mainly the time histories of the earthquake records are converted into the frequency domain by Fourier transform. The effect of earthquakes on the structures may be determined by the response spectra. For example, when the abbsolute acceleration spectra of an earthquake is known, the maximum shear force that will affect a building with a known natural period can be calculated easily. While the Fourier spectrum reflects the frequency-amplitude contents of earthquake waves, the response spectra reflect the maximum effect of the earthquakes on the structures which can be represented by a single mass system. So, it is obvious that the response spectra are more usefull from the engineering point of view. The best procedure for determining the site response of a particular location is to observe the ground motion during an actual event. This can be done by comparision of the strong motion data obtained on a sediment site and a reference site located on a firm ground. To achieve site response surveys in a reasonable period of time, this approach seems to be practical only in regions where the rate of seismicity is high. In many regions, the seismic activity is not so high as to be able to get an appropriate earthquake motion at any time and any place where a construction will be scheduled. Also, a network of strong motion recorders have to be installed in order to have an idea about the relative earthquke response characteristics of different regions. Determining the dynamic characteristics of local soil layers by means of in-situ and laboratory tests is a widely used method. But, as the cost of dynamic in-situ tests such as down-hole, cross-hole, seismic refraction, suspension P-S logging, etc. and laboratory tests such as dynamic triaxial test, simple shear test, resonant column test, etc. are too high, this method may not be considered as a convenient way for determining the dynamic characteristics of wide areas. The data obtained by in-situ and laboratory tests are used in theoretical soil models to determine the response charecteristics of soil layers. An alternative approch involves the use of ambient seismic noise called microtremors to estimate the earthquake site response. Microtremors are low amplitude oscillations of the ground surface produced by natural sources such as wind, ocean waves, geothermal reactions and small magnitude earth tremors. They can also be produced by artificial sources such as traffic, industrial activities etc. and this kind of artificial produced noise is called as cultural noise. Wave modes contributing to the mechanism of the microtremors have been inadequately defined. While some researchers accept them as surface waves, the others believe that they are body waves. In general, it appears that surface sources such as wind, ocean waves and cultural noise act as surface wave generators, whereas extremely small magnitude, naturally occuring earth tremors act as body wave xuistation were compared, it was seen that similar predominant periods appeared at these two spectra. When new settlements are planned or the potential earthquake site response of different regions that have been already settled wanted to be determined, microzoning studies have to be carried out. Especially for the crowded cities such as Istanbul, microzrination maps have to be prepared immediately. As the area of the city is very large, it will be very difficult to achieve an adequate microzoning study by means of in - situ or laboratory tests. In this study, it was shown that the earthquake response characteristics of the local soil layers could be successfully estimated by the use of microtremor data. As the time and money required for recording and analysis of microtremor data are low, microtremors seem to be an appropriate way for determining the earthquake response characteristics of soil layers. From the engineering point of view, microtremors offer very attractive advantages to the geotechnical engineers who need to have knowledge about the dynamic characteristics of the soil layer especially for microzoning studies. It is believed that, in Istanbul a microzonation study based on microtremor data will be very usefull for engineering purposes. As the cost of the operation and time required to get results are low relatively, using the microtremor Fourier spectra for determining the predominant periods of the local soil layers or using the microtremor spectral ratios for determinig the relative amplification ratios seem to be the best way for the cities such as Istanbul. xviMexico earthquake (M=8). In this event, despite of epicentral distance of several hundred kilometers, the ~2 sec fundamental vibration mode of the Mexico City lake- bed zone was reached and severe structural damages that led to thousands of casualties was caused due to the resonance. When the natural period of the structures are equal to the predominant periods of soil layers, than double resonance occurs. The spectral analysis is widely used in determining the characteristics of earthquake ground motions. In spectral analysis, mainly the time histories of the earthquake records are converted into the frequency domain by Fourier transform. The effect of earthquakes on the structures may be determined by the response spectra. For example, when the abbsolute acceleration spectra of an earthquake is known, the maximum shear force that will affect a building with a known natural period can be calculated easily. While the Fourier spectrum reflects the frequency-amplitude contents of earthquake waves, the response spectra reflect the maximum effect of the earthquakes on the structures which can be represented by a single mass system. So, it is obvious that the response spectra are more usefull from the engineering point of view. The best procedure for determining the site response of a particular location is to observe the ground motion during an actual event. This can be done by comparision of the strong motion data obtained on a sediment site and a reference site located on a firm ground. To achieve site response surveys in a reasonable period of time, this approach seems to be practical only in regions where the rate of seismicity is high. In many regions, the seismic activity is not so high as to be able to get an appropriate earthquake motion at any time and any place where a construction will be scheduled. Also, a network of strong motion recorders have to be installed in order to have an idea about the relative earthquke response characteristics of different regions. Determining the dynamic characteristics of local soil layers by means of in-situ and laboratory tests is a widely used method. But, as the cost of dynamic in-situ tests such as down-hole, cross-hole, seismic refraction, suspension P-S logging, etc. and laboratory tests such as dynamic triaxial test, simple shear test, resonant column test, etc. are too high, this method may not be considered as a convenient way for determining the dynamic characteristics of wide areas. The data obtained by in-situ and laboratory tests are used in theoretical soil models to determine the response charecteristics of soil layers. An alternative approch involves the use of ambient seismic noise called microtremors to estimate the earthquake site response. Microtremors are low amplitude oscillations of the ground surface produced by natural sources such as wind, ocean waves, geothermal reactions and small magnitude earth tremors. They can also be produced by artificial sources such as traffic, industrial activities etc. and this kind of artificial produced noise is called as cultural noise. Wave modes contributing to the mechanism of the microtremors have been inadequately defined. While some researchers accept them as surface waves, the others believe that they are body waves. In general, it appears that surface sources such as wind, ocean waves and cultural noise act as surface wave generators, whereas extremely small magnitude, naturally occuring earth tremors act as body wave xuistation were compared, it was seen that similar predominant periods appeared at these two spectra. When new settlements are planned or the potential earthquake site response of different regions that have been already settled wanted to be determined, microzoning studies have to be carried out. Especially for the crowded cities such as Istanbul, microzrination maps have to be prepared immediately. As the area of the city is very large, it will be very difficult to achieve an adequate microzoning study by means of in - situ or laboratory tests. In this study, it was shown that the earthquake response characteristics of the local soil layers could be successfully estimated by the use of microtremor data. As the time and money required for recording and analysis of microtremor data are low, microtremors seem to be an appropriate way for determining the earthquake response characteristics of soil layers. From the engineering point of view, microtremors offer very attractive advantages to the geotechnical engineers who need to have knowledge about the dynamic characteristics of the soil layer especially for microzoning studies. It is believed that, in Istanbul a microzonation study based on microtremor data will be very usefull for engineering purposes. As the cost of the operation and time required to get results are low relatively, using the microtremor Fourier spectra for determining the predominant periods of the local soil layers or using the microtremor spectral ratios for determinig the relative amplification ratios seem to be the best way for the cities such as Istanbul. xvi
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