Sismik izleme, sadece tektonik kökenli olayları değil aynı zamanda doğal veya kazara gerçekleşen olaylara da ışık tutabilecek potansiyele sahiptir. Sismolojinin bir kolu olan adli (forensic) sismoloji, dünya genelinde soğuk savaş sırasında ortaya çıkmıştır. Çeşitli ülkelerin nükleer silahları geliştirme hamleleri ve geliştirilen silahların test edilmesi safhalarında meydana gelen sismik sinyallerin sismoloji bilimi tarafından izlenebilme yeteneğinin fark edilmesi dünyada merak uyandırmıştır. Sismolojik analizlerle adli olaylara ait oluş zamanının, konumunun, büyüklüğünün, patlayıcı miktarının belirlenmesi ve patlamanın oluş düzeni gibi bilgiler elde edilebilmektedir. 5 Eylül 2012 tarihinde Afyonkarahisar'daki 500. İstihkâm Ana Depo Komutanlığı Şehit Uzman Çavuş Mete Saraç Kışlası'nda bulunan 32 nolu mühimmat deposunda kuvvetli bir patlama meydana gelmiştir. El bombalarının tasnif edilmesi esnasında meydana gelen patlama can ve mal kayıplarına neden olmuştur. Patlama esnasında sismik dalgaların yanı sıra yüksek basınçlı şok dalgaları oluşmuş ve bunlar bölgeye yakın olan sismometreler tarafından kaydedilmiştir. Bu çalışmada patlamaya ilişkin sismik ve akustik dalga kayıtları KOERİ ve AFAD istasyonlarından temin edilmiş ve zaman ve frekans ortamında incelenmiştir. Sismografların analizinde patlamanın 18:07:53.87 (UTC)'de gerçekleştiği tespit edilmiştir. Süreye ve yerel bağlı büyüklükleri sırasıyla Md=1.4 ve ML=1.4 olarak hesaplanmıştır. Patlamaya ilişkin konum tahmini ise güvenilir bir şekilde elde edilmiştir. Patlamada ne kadar malzemenin infilak ettiği sorusu ise krater çapı, ikincil şok dalgası gecikme süresi ve olay büyüklüğünü temel alan metotlar kullanılarak aydınlatılmaya çalışılmıştır. Üç verim tahmini yönteminden ikincil şok dalgası gecikme süresi temel alınarak yapılan verim tahmini patlayıcı malzemenin kimyasal özelliklerini hesaba katması ve sismogramlardan ikinci şok dalga gecikmelerinin net olarak tespit edilebilmesi nedeniyle diğer metotlara göre daha güvenilir bulunmuştur. Böylece infilak eden madde miktarı 21 ton olarak tespit edilmiştir. Frekans ortamı çalışmalarında P dalgalarının 3 Hz ve akustik dalgaların ise 20 Hz civarında baskın olduğu belirlenmiştir. Ayrıca çok kısa sürede birden fazla patlamanın gerçekleştiğine dair frekans ortamı analizlerinde bulgulara rastlanmıştır. Sismolojik araştırmalar terör saldırıları, büyük patlamalar ve çeşitli doğal olamayan olayların oluş süreçlerinin aydınlatılmasına bilgi sunmaktadırlar. Bu sayede acil durum planlamalarına katkılar sağlanabilir ve adli süreçlere ışık tutulabilir.
Forensic sciences are defined as a bundle of sciences contributed by a large number of sciences used to reveal crimes and disputes. Although forensic sciences have not gained the identity of a science on its own, it can be described as a general collection of different disciplines (geophysics, geology, medicine, chemistry, biology, psychology, social science, etc.). The concept of forensic event can be defined as the events that are investigated by law enforcement officers, prosecutor's office and courts ex officio or through a complaint and that have an element of crime within the scope specified in criminal law. In order to clarify these events, the collection of crime scene and all kinds of evidence related to the crime provides significant benefits. In parallel with the development of earth sciences in recent years, its contributions to other different disciplines are significant. Geology, Geophysics, Geochemistry and their sub-disciplines (seismology, mineralogy, sedimentology, geomorphology, etc.) are used to make great contributions to forensic investigations. In recent years, detailed analyses of natural and unnatural seismic sources have been used as a tool to contribute to investigations. Seismology, one of the main branches of geophysical engineering, studies earth movements and earthquakes. An important branch of this main science is forensic seismology. Forensic seismology emerged worldwide during the Cold War. The realisation of the ability of seismological science to monitor the seismic signals that occur during the development of nuclear weapons by various countries and the testing of the developed weapons has aroused curiosity in the world. The fact that seismic signals can often be detected many kilometres away from the sites of explosions quickly made it clear that seismological methods are a powerful tool for monitoring these tests. One of the biggest challenges in forensic seismology is to distinguish between seismic signals generated by earthquakes and those generated by explosions. Today, many researchers have made significant contributions to the literature on this subject. The rapidly developing seismological observatories around the world have resulted in numerous examples of how seismic observations are potentially being used to support forensic investigations. Important examples include the use of seismic and acoustic signals to estimate the time of impact and location of aircraft crashes, to estimate the time of detonation and quantity of explosives after terrorist attacks, to detect underground nuclear tests, to estimate the details of chemical factory explosions, and to analyse explosive burglaries. Natural and artificial seismic sources represent movements in the earth's crust. Natural seismic sources refer to seismic waves caused by earthquakes and other movements in the earth's crust. Some of the energy generated is propagated in the form of seismic waves and recorded by seismometers. Artificial seismic sources are sources of vibration or energy produced deliberately or accidentally by humans. Artificial vibrations are generated as a result of forensic events such as factory explosions, terrorist attacks, aircraft crashes and some of them are recorded by devices. Both natural and artificial seismic sources serve to understand the internal structure and movements of the Earth's crust. Earthquakes and explosions release enormous amounts of energy into the environment when they occur. In terms of waveforms, since the forces related to these events are different, there are differences in waveforms. Explosions occur in very shallow parts of the earth's surface. All the energy released during their realisation is emitted from a volumetrically small source. When the force mechanism of explosions is analysed, there is a force mechanism with equal forces in all directions. If a large explosion occurs, a chemical reaction starts rapidly. As the reaction progresses, the explosive material turns into a very dense, very hot and highly pressurised gas. At the beginning of the explosion, the explosive material attempts to equilibrate with the ambient air at high temperatures and a high-pressure shock wave is released. Shock waves are powerful pressure waves generated by events (e.g. explosions) that produce severe changes in pressure in an elastic medium. The wave front where compression occurs is a region of sudden and violent changes in stress, density and temperature. Shock waves therefore propagate differently from acoustic waves. Shock waves travel faster than sound and their speed increases as the amplitude increases. The intensity of spherical shock waves caused by explosions decreases rapidly as they move away from the centre of the explosion and becomes equal to the speed of sound (average 340 m/s under standard conditions). The intensity of the shock wave decreases faster than the intensity of the acoustic wave. Acoustic waveforms have a sharper onset and shorter duration than seismic waveforms. Acoustic and seismic waves can be recorded by seismometers and observed in seismogram. On 5 September 2012, around 21:15 local time, an explosion occurred during the sorting of hand bombs at the ammunition depot in Afyonkarahisar. 25 soldiers were martyred in the explosion. In addition, 8 people, including 4 soldiers, were seriously injured. After the explosion, unexploded grenades, tank bombs, mines and pieces of ammunition were scattered as far as Çiftlik, 500 metres away. The explosion, which was felt from a distance of approximately 20 kilometres, caused the destruction and burning of trees in the vicinity. Significant damage was also observed in military facilities. In the damage assessment studies conducted by the Disaster and Emergency Management Presidency (AFAD) teams, it was reported that a total of 240 houses and 16 vehicles were damaged in Afyon Kışlacık village and Ataköy neighbourhoods. It was stated that the main cause of damage was the pressure waves caused by the explosion. In this study, the explosion will be evaluated seismologically. For this purpose, it is aimed to obtain information such as the time of occurrence, determination of the amount of explosives, the order of the explosion and to produce information that can be useful for emergency planning and administrative investigations. Different types of seismic events were analysed in time and frequency domain. The zSacWin EQ Processing computer software was used to analyse and display the data. Seismic Analysis Code (SAC) analysis package was preferred for analysing the waveforms of seismic events in time and frequency domain. SAC is a free software package that is widely used for general analysis and processing of seismic data (remote or regional). With SAC, seismic events can be displayed in time domain, Fourier amplitude spectra and spectrograms can be obtained. In addition, it is of great importance to determine the amount of explosive material after a seismic event in order to shed light on forensic investigations. There are many methods in this context. In the following sections, frequently used ones will be detailed. Seismic stations of two different seismological observatories are located in the area where the explosion occurred. Seismic stations of Kandilli Observatory and Earthquake Research Institute-Regional Earthquake and Tsunami Monitoring Centre (KRDAE-BDTIM) and Disaster and Emergency Management Presidency Earthquake Department (AFAD-DDB) were used in the investigations. Stations with clearly identifiable seismic arrivals recorded by regional seismic networks were preferred in the analyses. It was determined that the explosion was recorded by 9 three-component broadband seismic stations (weak motion) at a distance of approximately 36 to 181 km from the location of the explosion. The closest station to the explosion, BOLV (epicentre distance ≈ 36 km), is located east of the explosion. In the analyses of 9 stations, acoustic waves were observed only in the seismogram of the nearest BOLV station. The zSacWin EQ Processing computer software was used to determine the location, origin time and magnitude of the explosion. Based on the arrival times of P and S waves read from the seismograms, the location of the explosion was determined at coordinates 38.6957oN-30.5102oD. The original time of the explosion was determined to have occurred at 21:07:53 local time (18:07:53 GMT). The local and duration dependent magnitudes were calculated as Md=1.4 and ML=1.4, respectively. The velocity of P wave was determined by using the arrival times of P waves. For this purpose, P wave arrival times were obtained for each station and wave velocity was determined by linear regression. Vp wave velocity was determined as 6.3 km/s. The acoustic wave velocity calculated based on the BOLV station is 356 m/s. If the explosive material is known when an explosion occurs, the amount of detonating material can be obtained by experimental relations. In addition, the amount of detonating material can be determined by using different types of parameters. In this study, for the 2012 Afyon ammunition depot explosion, three different methods such as crater dimensions, magnitude-yield estimation calculated using seismic waves, and finally the secondary shock wave parameter obtained from acoustic waves were used to estimate the yield. Firstly, it is a calculation method based on the dimensions (depth and diameter) of the crater formed after the explosion for yield estimation. According to the 2012 Afyon ammunition depot expert reports, no crater was found in the depot. There is only a crater with a diameter of 3 metres at the right front entrance of the armoury. It was stated that this crater was caused by another small explosion. According to the available data, a calculation based on the diameter of the crater shows that 0.89 tonnes of explosive detonated. Another method is the secondary shock wave method. Using the equations given by Rigby and Gitterman (2016), the mass of the explosive can be determined with the secondary shock wave of the 2012 Afyon explosion. 'PETN', i.e. plastic explosive chemical, was detected at the scene in the expert reports. The Vod value of this explosive substance is 8300 (m/s) and the density of the explosive substance ρ is 1.77 (kg/m3). Based on this information, it was determined that 20 880 kg ∽ (21 tonnes) ± 2% of a material detonated. This value is the weight of the material detonated in the explosion expressed in tonnes. Another method is to estimate the size of the explosion. With this method, the amount of explosive detonated was estimated as 7.1 t. In the 2012 Afyon ammunition depot explosion, no crater was reported inside the depot. The estimate based on the small crater reported outside the depot is far from the truth. The estimate based on the magnitude of the event calculated from seismic waves represents only the lower limit of the explosion. Considering that most of the energy transfer to the atmosphere takes place by shock waves, the estimation made with this method is largely incomplete. In order to estimate the yield using secondary shock wave delay time, detailed parameters such as explosion velocity and compound density of the detonating material, scaled distance and delay times that can be clearly read from seismograms are used. This increases the precision compared to other methods. When all these conditions are evaluated, it is considered that the yield estimation with the secondary shock wave delay time is closer to reality and more accurate for the 2012 Afyon ammunition depot explosion. Analysing the waveforms of seismic events in the frequency domain reveals how the spectral content changes with time. In the analyses, Fast Fourier Transform (FFT) was used to show how the amplitude changes with frequency and spectrograms of the burst were obtained to observe how the signal strength changes as a function of time at different frequencies. For the BOLV station, Fast Fourier Transform (FFT) was used to show how the amplitude changes with frequency and spectrograms were obtained to observe how the signal strength changes as a function of time at different frequencies. In the frequency environment analysis, it was determined that P waves were dominant around 3 Hz and acoustic waves were dominant around 20 Hz. In addition, there were findings in the frequency environment analysis that more than one explosion occurred in a very short period of time. In recent years, the number and quality of seismic networks has been increasing all over the world, especially for the study of earthquakes. With detailed seismic monitoring, detailed information on events subject to forensic investigations such as explosions can be obtained by analyzing the records of these seismic stations. In the aftermath of powerful explosions, a large amount of information such as the origin time, size and amount of material exploded can be quickly obtained without being affected by the chaos of search and rescue operations. In the light of the reliable information obtained, emergency planning and administrative investigations can benefit.
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