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Artalan Sismik Gürültüler (ASG), yerkürenin, gerek kendi içindeki hareketlenmeleri gerekse de dış etkenlerle etkileşimi sonucunda sismik enerjinin açığa çıkmasıyla oluşan farklı periyot bantlarına sahip cisim ve yüzey dalgalarıdır. Daha önceleri veriyi kirlettiği gerekçesiyle istenmeyen ve süzgeçlenerek bastırılmaya çalışılan gürültü sinyalleri son yıllarda geliştirilen yöntemlerin de katkısıyla, yüzey dalgalarından Green fonksiyonu eldesi ile kabuk ve manto hız yapısının araştırılması, petrol aramaları, zemin araştırmaları gibi pek çok çalışmada veri olarak kullanılmaktadır. Aynı zamanda gürültünün nitelendirilmesi dünyada binlercesi kurulu olan sismografların performansını daha iyi anlamaya ve veri kalitesini artırmaya yardımcı olacaktır. Bu tez çalışmasının amacı, nüfusu yüksek, endüstriyel anlamda gelişmiş ve tektonik olarak aktif bir coğrafyada bulunan sedimanter Adana Havzası ve çevresinin sismik gürültü niteliğinin zamana, konuma, jeolojiye ve kültürel yapılarak bağlı olarak araştırılması ve değerlendirilmesidir. Çalışmada kullanılan 2011 ve 2012 yıllarına ait sürekli sismik kayıtlar, Boğaziçi Üniversitesi Kandilli Rasathanesi Deprem Araştırma Enstitüsü (KRDAE) ve T.C Başbakanlık Afet ve Acil Durum Yönetimi Başkanlığı Deprem Dairesi Başkanlığı (AFAD-DAD)' na ait, Adana Havzası' nda bulunan 17 adet geniş bantlı Güralp CMG-3T ve Güralp CMG-3ESP marka hız kayıtçıları ile toplanmıştır. Havzanın sismik gürültü değerlendirmesine geçmeden önce yöntem ayrıntılarının verilmesinin yanı sıra programı ve kullanılacak verileri tanımaya yönelik bir takım çalışmalarda bulunulmuştur. Uygulanan gürültü analizi yönteminde, düşey bileşenli verilerin güç yoğunluğu spektrumları (GYS), olasılık yoğunluk fonksiyonları (OYF) ve spektrogramları açık kaynaklı PQLX (Passcal Quick Look eXtented) programı kullanılarak hesaplatılmış ve çizdirilmiştir. Havzadaki gürültü dağılımının zamana ve konuma bağlı değişiminin incelenmesi için GMT programı kullanılarak hazırlanan haritalarda, kültürel gürültülerin yani mikrotremörlerin (kaynak: trafik, insan, makine vb.) baskın olarak gözlendiği 0.1-1 s bandı ve mikrosalınım olarak da bilinen mikroseizmların (kaynak: derin ve sığ su etkileşimleri) gözlendiği 4-8 s (İkincil Yüksek Frekans veya Double Frequency Peak) ve 10-20 s (Birincil Yüksek Frekans veya Single Frequency Peak) bantlarındaki gürültü verileri, 2011 yılı, yaz-kış mevsimleri ve gece-güz saatleri için haritalanmıştır. Öte yandan kıyıya yakın bir istasyon ile karasal ortama kurulmuş ve aynı jeolojik formasyon üzerindeki istasyon arasındaki farklar spektrogramları hesaplanarak incelenmiştir. Bölgede üç bileşen xviii kaydı mevcut olan KRDAE verileri kullanılarak gürültülerin mod değerlerinin yatay ve düşey bileşenlerdeki durumu incelenmiş ve gözlenen farklar tartışılmıştır. Elde edilen sonuçlara göre gün içindeki gürültü seviyesi değişimlerinin yüksek frekanslı kültürel gürültülerden kaynaklandığı gözlenmiştir. Mevsimler arasındaki değişimler ise ancak uzun periyotlarda gözlenebilmiştir. Genel olarak, kültürel gürültüler yerleşimin ve sediman kalınlığının fazla olduğu havza içinde her zaman yüksek değerlerde gözlenirken, uzun periyotlu mikrotitreşimlerin daha çok havza sınırlarını etkilediği söylenebilir. Çalışmada 2011 yılı düşey bileşen kayıtlar için periyoda bağlı elde edilen en yüksek ve en düşük mod değerleri grafiklenerek bölgeye ait yüksek ve düşük gürültü modeli oluşturulmuştur. Bu çalışma ile bölgedeki istasyonların ve toplanan verinin kalitesi hakkında bilgi sağlanmıştır. Özellikle bazı istasyonlarda veri kayıtlarının sürekli olmadığı veya alet kökenli arızalar nedeniyle veri kalitesinin bozulduğu gözlenmiştir. Kullanılan yöntem, kurulu istasyonların sürekli izlenmesi ve arızaların öngörülüp zamanında müdahale edilmesine ve dolayısı ile veri kaydı sürekliliğine katkı sağlayabilir. Çalışmada elde edilen en yüksek ve en düşük gürültü modeli ve gürültü haritaları, bundan sonra bölgeye yerleştirilecek güncel istasyonlar için referans model olarak kullanılabilir. Gürültü seviyesi düşük bölgeler daha düşük manyitüdlü depremlerin kayıtlarına olanak sağlayabilirken, yüksek gürültülü bölgelerde manyitüdü daha büyük depremler kayıt edilebilecektir. Bu çalışmada elde edilen bilgiler yine gürültü verilerinin kullanılacağı dizilim işleme, yatay/düşey spektral oranlama, artalan sismik gürültü tomografisi, zemin özelliklerini ve sediman kalınlığını belirlemeye yönelik gürültü kökenli birçok çalışmada referans olarak kullanılabilir. The ambient seismic noise is widely used in imaging the subsurface structure. One of the popular applications is the retrieval of surface waves Green's functions that are used to obtain the velocity distributon in the Earth's crust and mantle. Ambient noise is also used in oil exploration and in near-surface studies for soil characterizations. In such studies the characterization of the noise can help to better understand the performance of each seismograph and the noise levels at each station which can contribute to interpretations of the results obtained by other ambient noise studies. In this study the characteristics of background seismic noise levels in the Adana Basin and its surroundings (Southern Turkey) are investigated. The Adana Basin is an inter-mountain, NE-SW trending basin. The depositional history, geological formations and thickness of the sediments suggest high potential for hydrocarbon settings. Besides, it is a developing region both in population and industry, a tectonically active area and hence prone to seismic hazards. Several studies are performed or under progress to understand the subsurface structure of the region. The characterization of the quality of noise data and the ambient seismic noise levels of the region may contribute to the ongoing and future studies, such as tomography, array processing and H/V spectral ratio studies, based on ambient noise. For this purpose the continuous noise data is processed recorded in 2011 by the noise analysis method given in Chapter 2. Adana Basin and its surroundings, is an arcuate, open V shape structure extending in NE-SW direction in the northeastern Mediterranean Sea. The basin is developed on Tauride basement rocks mainly in Neogene times, affected by the interplay of the African plate with the Arabian and Anatolian microplates. The basin is primarily controlled by NE-SW trending faults that are splays of the larger sinistral East Anatolian Fault. Three main rivers occupy the Adana Basin and form a major deltaic complex in the region. The previous studies suggest a sediment thickness between 3 km to 6 km. The aim of this study is to characterize the seismic noise and the quality of the continuous noise data in the region which will contribute to the recent and future seismic studies. For this reason, the vertical component continuous data recorded during 2011 by seventeen broadband Guralp CMG-3T, Güralp CMG-3T and Güralp CMG-3ESP velocity sensors with sampling rates 50 and 100 sps are used. The national seismic networks in the investigated sites are operated by KOERI (Kandilli Observatory and Earthquake Research Institute) and ERD (Earthquake Research Department of Disaster and Emergency Management Presidency of Turkey). xx In a continuous seismic record, besides noise, earthquakes, system transients and instrumental glitches (data gaps, clipping, spikes, mass recenters, calibration pulses) will be present. For the characterization of the noise, removal of this kind of distortions is necessary. In the method mentioned in Chapter 2 the discrimination of these distortions are provided by the calculation of the probability density functions (PDFs) of the seismic data. As the distortions are represented by low probabilities, the power values with high probabilities correspond to stationary background noise at each station. Details of system transients and instrument glitches are given in Chapter 3 with some demonstrations of seismic traces and PSD curves. In Chapter 4, investigation of spatial and temporal noise properties in the Adana Basin and its surroundings are studied. At last, final comments and results are discussed (Chapter 5). In this study the open source software Passcal-Iris Quick Look eXtented (PQLX) is use for processing the data. The data is prepared by selecting 1-hr time series segments with an overlap of 50%. Each 1-hr segment is divided into 13 segments with 75% overlap to reduce variance of the power spectral density (PSD) estimates. After removing the mean, trend and instrument response, 10% cosine taper is applied to the ends of the time series to reduce the spectral leakage in the resulting Fast Fourier Transform (FFT). After computing the PSD of each time series segment the results are converted to ground acceleration to compare with the NLNM and NHNM. After calculating the PSDs and PDFs, first results show that the main features of noise are coherent in general with the new low-noise model (NLNM) and new high-noise model (NHNM) of Peterson noise models but different at few localities. These features are cultural noise (T=0.1-1s, noise source: traffic, machinery) and microseisms that are classified as Double Frequency Peak (DFP, T=4-8s, noise source: ocean waves) and Single Frequency Peak (SFP, T=10-20s, noise source: shallow coastal waters). Before the noise characterization, the usage and properties of PQLX, its inputs and outputs, arrangement of the suitable response function format, organization of the data set's header informations etc. are investigated and applied. In order to investigate the noise characteristics in the basin and its surroundings, PSD mode values are used for the cultural noise and microseism periods and noise distribution maps are prepared for annual, seasonal and diurnal variations by using GMT (Generic Mapping Tools). To observe the annual noise changes, PSD mode values for the 3 different period band have mapped for the year of 2011. For the cultural noise band (T=0.1-1s), it is clearly seen that the noise level is higher than the other bands (DFP, SFP) and high noise propagates from the coast region towards the basin. For the DFP band (T=4-8s), relatively higher noise level stands near the border of the basin and also cay station which has always the highest noise level in the basin. For the SFP band (T=10-20s), there is a sharp noise decreasing as near as 30 dB through the whole basin, but still middle of the basin has higher noise values. To observe the seasonal noise changes, summer months (June, July, August 2011) and winter months (December 2011, January-February 2012) are processed. In the cultural noise band, noise distribution in summer is more extensive and propagates from all coastal side into the basin; in winter, high noise level distribution remains only on the coastal side. Contrarily, for the DFP band, noise variationss are observed only on the borders of the basin except cay in summer, while almost whole study xxi area has affected by the high noise such as -120 dB and -130 dB in winter. Lastly, for the SFP band, again there is a sharp noise level decreasing for both seasons, but it is seen that, in winter, especially Adana Basin and around the Taurus Mountain (Northwest of the study area) has relatively high noise values. In addition to these noise maps, to observe the seasonal changes with different graphs, spectrograms were analysed for two different seasons as wet and dry seasons. To observe the daily noise changes, the day (06:00-20:00) and the night (20:00-06:00) times data are mapped. For the cultural noise, the day time shows high noise levels especially near the coast and in the basin region. This high noise level reduces about 10-20 dB at the night times. For the DFP, there is no significant variation between day and night times. At SFP both for the day and the night times, the noise levels in the basin are higher in comparison to mountain sides. The relatively high noise levels in the basin are spread to wider area in the day time when compared to the night times. Consequently, in daily basis, the significant variations occur at cultural noise levels, almost no variation is observed at SFP, and slight variations are observed at DFP periods. In addition to three specific period band that defined above, for the 0.5-3s band, we observe the DFP changes during a year and half yearly. It is seen that, local sea wave activity affects the noise level, bathimetry changes could also be a good reason for these changes. Besides the noise map interpretations, some other investigations are also studied and some are briefly mentioned as follows. Noise level difference between the coastal and the crustal based stations which installed on the same geological structure is studied by the analysis of the spectrograms. Also, as three-component data sets are available for the KOERI stations, those mode values are graphed for the seven stations and it is seen that the horizontal components (E, N) have higher noise levels with respect to vertical (Z) component in high periods. Vertical-component PSD mode curves for 17 stations are coherent with the Peterson noise models. The Adana Basin mode high- and low- noise models are estimated which will provide useful information before the installation of any station and also in earthquake magnitude interpretations. In this study, unfortunately it is observed that at some stations the data quality is poor due to the interruption of data transfer, mass recenter and similar reasons, therefore significant part of the data could not be used in processing. For the future studies, the PSD calculations for the year 2012 and for the horizontal components of the time series are under progress. Afterwards array processing and the horizontal to vertical spectral ratio (HVSR) studies will be performed for the region for further characterization of both noise and subsurface structure. 101