Attenuative behaviours of western Anatolia and southern Spain using single and multiple scattering models
Başlık çevirisi mevcut değil.
- Tez No: 35939
- Danışmanlar: PROF. DR. A. GÜNGÖR TAKTAK
- Tez Türü: Doktora
- Konular: Jeofizik Mühendisliği, Geophysics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1994
- Dil: İngilizce
- Üniversite: Dokuz Eylül Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Jeofizik Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 279
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Özet (Çeviri)
ABSTRACT By analyzing the decay of coda wave amplitude, coda Q, Qc, have been determined in the Western Anatolia (Turkey). Using the Single Isotropic Scattering Model, 116 earthquakes which registered at the GEBZE station were analyzed for five narrow frequency bands centered at 1.5, 3, 6, 8 and 10 Hz. Coda Q values were obtained using different lapse times, between 30 to 190 seconds, in steps of 10 seconds. Coda Qc for Western Anatolia depends on frequency and lapse time. For a lapse time of 30 seconds, the frequency dependence ofQc is Qc(f)=50.7fl-°] and for a lapse time of 190 seconds, it is Qc(f)=183.2j0-76. in this region, the exponential value of the Qc frequency of dependence is practically constant, between 0. 7 and 1.0. The obtained coda Qc values were compared with others estimated in different regions. The coda Qc for lapse times between 60 to 100 seconds for Western Anatolia and Southern Spain are practically the same, indicating similar coda waves attenuation patterns in both regions of the Mediterranean Basin. A separation of intrinsic and scattering attenuation in two iectonically active areas of the Mediterranean Basin, Southern Spain and Western Anatolia has been obtained using the Multiple-Lapse Time Window Method. In Southern Spain, Qs is predominant over Qi for frequencies lower than 4 Hz; between 4 to 8 Hz, results show similar scattering and intrinsic attenuation. For frequencies higher than 8 Hz, intrinsic attenuation is clearly dominant over scattering. Le~J does not change uniformly with frequency; it increases until 8 Hz and decreases at frequencies greater than 8 Hz. The integrated energy curves of Western Anatolia do not show regular change with distance. For the first energy window (0-15 seconds), there is a clear increase of the energy with distance between 0 to 80 km and then, a decrease after 80 km. The fit of the experimental data in the full hypocentral distance range is not good. The experimental energy curves were divided into two different segments, 0-80 and 80- J 70 km. In 0-80 km, Bq is close to 1 and the Le~l values are low (0.004-0.013). In the second distance range (80-170 km) intrinsic attenuation is predominant over scattering. Qs~l is more frequency dependent than Qf1, (This is i.e. f1-47 against f1-29)- It was observed that coda Q-l is equal to the observed Qi~l for intermediate frequencies, in both regions. However, Qc~l is really similar to Qsrl for short distances and is located between Qi and Qs for long distances in Southern Spain at low frequencies. Qc is similar to the observed Qt in both regions at high frequencies. The poor fit of the simulated curves with experimental data can be explained by introducing geometrical spreading values different than ones used here. It is necessary to improve the used model taking into account phenomena like, non isotropic scattering, variation of attenuation with depth or a geometrical spreading value different than the theoretical value used The attenuation of Lg waves for crustal paths in Western Anatolia and Southern Spain were compared with other regions over source-receiver distances of about 100-400 km. The coda normalization method which was used here, is based on elimination of the source and site effects from observed spectra of Lg waves. Q for Lg waves in the crust and upper mantle was determined as a function of frequency in the range 1.5-10.0 Hz for Western Anatolia, 1.5-12 Hz for Southern Spain. Then, the decay with distance of coda normalized Lg wave amplitudes with frequency dependent Q and also geometrical spreading exponent were parametrized We found the Qlâ?? shows a strong dependence on frequency in both regions. The decay of Lg waves amplitudes from 1.5 to 10 Hz in Western Anatolia is fit with a frequency dependent Q\g as a form ofQig(f)=83fl-0 and geometrical spreading around 0.6-0.7. For Southern Spain, it was found a Lg wave Q as a frequency dependent, Qlg(f)^82fl-^, with geometrical spreading approximately 0.5.
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