INVESTIGATING OF RELATIVE CRUSTAL THICKNESSES VARIATION OF CRETAN REGION WITH MAGNETIC AND FREE AIR GRAVITY ANOMALIES

Girit yayı bölgesi Doğu Akdeniz'de aktif dalma-batma olgusunun devam ettiği Afrika ve Ege levhalarının etkileştiği bir bölgedir. Bu bağlamda Girit yayı Doğu Akdeniz tektoniğinin en karmaşık alanıdır. Bu yapıyı açıklamak için 230 00ı-280 00ı doğu boylamları ve 330 00ı-360 40ı kuzey enlemleri arasında kalan bölgenin serbest hava gravite ve manyetik anomalilerinden kabuk yapısı araştırılmıştır. Bu anomalilerin değerleri arasında kabuk kalınlıkları belirlenmesinde ters bir orantı mevcuttur. Dolayısıyla bu yaklaşım göreceli kabuk kalınlıkları hakkında genel bilgileri vermektedir. Girit adasının güney kısmında kabuk kalınlığı kuzeydekine göre daha fazla olduğu ve Ege Denizi içlerinde kabuk kalınlığının adanın güneyine göre daha ince olduğu hem gravite hem de manyetik anomalilerin ortak değerlendirilmesi ile ortaya konmuştur. Sonuç olarak bu uygulama özellikle göreceli kabuksal kalınlık değişiminin ilksel alan değerlendirmelerinde yardımcı olacaktır. Cretan Arc area where the plates of Africa and Aegean converge, is an active subduction still undergoing. In this respect the Cretan Arc is one of the most complex within the Eastern Mediterranean tectonics. In order to explain this structure, the crustal structure of this area lying in the coordinates 230 00ı-280 00ı east longitudes and 330 00ı-360 40ı north latitudes was tried to be investigated with free-air gravity and magnetic anomalies. There is a reciprocal relationship between the anomalies for determining crustal thicknesses. Therefore this approach can give general information about relative crustal thicknesses. The crustal thickness are thicker in the south of the Island of Crete compared with its north and accordingly the crustal thickness get relatively thinner toward the inward of the Aegean Sea observed from the both gravity and magnetic anomalies

Examination of the kinematic structures in İzmir (Western Anatolia) with repeated GPS observations (2009, 2010 and 2011)

The Western Anatolia and the Aegean Sea regions are one of the most significant seismically active and rapidly deforming fields in the world. Generally, seismic activities cause deformations and these deformations are monitored with Global Positioning System (GPS) /Global Navigation System (GNSS). In this context, GPS data were used to determine the deformation of İzmir and its surrounding to estimate the relative plate motions. In this study, the kinematic structures of the faults, which control the seismic hazard in İzmir and its surroundings, processing results of the three-year (2009, 2010 and 2011) episodic GPS observations and the estimation of displacements for 21 GPS stations were presented. The aim of this study is to examine interplate motion of the stations and their relations with the tectonic structures, seismicity and paleomagnetism and additionally, to interprete the motions of the study area relative to different block motions. Consequently, the mean motion of the study area was found approximately 25 mm/yr (towards the SSW) in the Eurasia fixed frame solution. The Aegean block fixed frame and the Anatolian block fixed frame solutions were computed relative to Euler vectors. In Aegean and Anatolian block solutions it was determined that the stations move separately, not as a group. In Euler pole solution, some stations are separated from each other and meanwhile some stations are grouped by considering the differences and similarities of the station motions. According to this solution three lines and two regions were described in the study area. The relations between seismicity and paleomagnetic studies and the kinematic structures determined in Anatolian block fixed frame and Euler pole solution were also investigated. When the Anatolian block fixed frame solution and the earthquakes occurred between the years 1973 and 2011 were evaluated together, it was found that in the high seismically active region especially near to Sığacık bay, the motions of GPS stations were different even though their locations were close to each other. As a result of this, the relationship between the vector directions and active tectonism was determined. Additionally, in the Euler pole solution directions of the motion were found to be coherent with the paleomagnetic results, particularly in Urla and its surroundings. Here, the block fixed frame and Euler pole solutions and additionally, relations of them with seismicity and tectonism were mentioned as difference from previous studies. Besides, in this study, high importance was given to locate each station in main geological formations of the study area. Keywords: GPS/GNSS; Western Anatolia; Izmir; Tectonic feature

Analysis and interpretation of the eastern Mediterranean geophysical data

Doğu Akdeniz Bölgesi'nin neotektoniğini, Afrika Plakası, Arap Plakası ve Avrasya Plakasının göreceli hareketleri denetlemektedir. Bölge, Anadolu Plakasının Kuzey Anadolu Fay Zonu (KAFS) boyunca batıya kaçması ve bu plakanın Yunan Kesme Zonunun etkisi ile Güney- Batı yönlü hareketi ile şekillenmektedir. Girit ada yayı ve buradaki dalma-batma zonu plaka hareketlerinin etkileşim mekanizması ile sürecini günümüzde halen devam ettirmektedir. Dolayısıyla günümüzde devam eden tektonizma özelliklerini ortaya koymak ve bölgeye genel bir tektonik model oluşturmak için 23-28 boylamları / 33-38 enlemleri ile sınırlandırılmış çalışma alanında sismoloji ve gravite verileri irdelenmiştir. Bu amaç doğrultusunda, sismolojik veriler USGS'ten, gravite verileri ise 1971-74 Shakleton çalışmalarından sağlanmıştır.Kabuk kalınlığının volkanik ada yayı boyunca izafi bir incelme içinde olduğu yay önünde ise göreceli parçalı incelme ve kalınlaşmaların olduğu Von Frese (1982)' deki yaklaşımı ile saptanmıştır. Özellikle Pliny, Strabo hendekleri boyunca sistemin doğrultu atımlı sisteme dönmesi ve Fethiye Burdur Fay hattı ile etkileşimi güneybatı Türkiye ana karasında oluşabilecek depremlerin irdelenmesi açısından da önem göstermektedir.Tüm yapılan bu çalışmalar ile bölgenin batimetrik ve tektonik bilgilerini kullanarak winlink modelleme programında modelleme uygulaması yapılmıştır. Elde edilen gravite modelleri moho derinliği değişimi ve kıtasal kabuk okyanussal kabuk sınırlarının tespitini sismolojik veriler ile destekleyerek ortaya çıkarmıştır. Neotectonics of the Eastern Mediterranean is still active and the motion of the African Plate, Arabian Plate and the Eurasian Plate controls it. The westward motion of the North Anatolian Fault Zone and southwestward rotation of the Aegean region shape this region. Therefore, to create the subduction model of the Cretan Arc, Seismological data (USGS) and gravity data (from 1971-74 Shakleton Cruise) of the region, which is defined by the 23-28 longitudes and 33-38 latitudes, were collected.Thickness of crust values were found relatively low along the volcanic arc same as Von Frese (1982). Especially, changing of the system around the Pliny, Strabo trenches (strike slip fault system) affect the structural conditions. Because of the undulated bathymetric values can be related the relative thickness differences in the southeast region of the Crete and these strike slip fault system to reach over to Turkey with Fethiye Burdur fault system. Therefore analyzing of this system is very important to solve tectonic problems in global focusing in coastal civilization in future.Finally, bathymetric and tectonic knowledge were combined and then Bouguer Gravity Anomaly Model were created with winlink software According to this geometry of subduction zone crustal thickness variations and moho depth were defined and characteristics of the region were described with seismological and gravity data

Availability of TOPEX V28.1 gravity data across the continent excluding seas; A case study, Western Anatolia example

In geosciences, satellite data are very important, where in-situ methods cannot be applicable. Especially the gravity data are very important for investigating the buried structures and discovering the changes of subterranean media alongside laterally. Nowadays, many global satellite models are used for solving these problems. The TOPEX V28.1 data set has a much more frequent sampling interval than other models. However, the TOPEX data set obtained in the general application is free air anomaly values. For this reason, researchers do not prefer TOPEX dataset for evaluation. In this study the target is using of TOPEX data set, which has a much more frequent sampling interval, to obtain Bouguer gravity values. These calculated new Bouguer gravity results have been compared with the results of the EGM08 and WGM2012 models to check coherence. The depth values which calculated by using the power spectrum method were investigated the findings have been compared with the result of the horizontal derivatives and finally findings of the general tectonic of the western Anatolian which obtained by using 3-D Euler depth solutions were discussed

Investigation of distribution of embedded shallow structures using the first order vertical derivative of gravity data

The utilization of the first order vertical derivative method, applied to a gravity field, in the determination of relatively low density and high density areas within the same unit can be helpful, defining such areas. In this study, the first order vertical derivative method was first applied to synthetic data and the workability of the method was investigated by creating scenarios having different densities within the same unit. Later, to compare the result of the scenarios, Adala-Manisa/Turkey and surroundings having a volcanic history were selected because of the existence of underground structures formed as a result of embedded volcanic areas. Real data set was obtained by using Scintrex CG-5 and Leica 1200 + GNSS for investigating the geological structure of the Adala-Manisa, at 400 stations. After the gravity reduction process the residual gravity anomaly values of the Adala-Manisa were obtained by removing a first order regional trend from the Bouguer gravity map. In the following process, the first order vertical derivative method was applied to the residual anomaly map. Thus, results of the synthetic anomalies and real data anomalies were compared and discussed by using the residual Bouguer gravity anomaly map. Consequently, the first order vertical derivative application in the determination of suppressed and undefinable shallow weak resources in the same media as Alluvial Fans and Alluvium units, especially on the Bouguer gravity anomaly map produces acceptable effective results. (C) 2014 Elsevier B.V. All rights reserved

Structure of the Hellenic Subduction Zone from Gravity Gradient Functions and Seismology

The Normalized Full Gradient (NFG) method has widespread applications in the analysis of potential fields, especially the gravity and magnetic fields. This method is used to identify the lateral and horizontal density variations in the crust and lithosphere. In this study, the NFG method was applied to the gravity data of the Cretan Arc and its surroundings. Because of the tectonic features of the eastern Mediterranean, the Cretan Arc and the neighboring areas are seismically very active. Especially the subduction zone and the complicated crustal features have been defined applying many different geophysical methods. In this study, first the NFG method is tested with synthetic prisms (two cubes). After that, the NFG method was applied to the Bouguer gravity data of the Cretan Arc and its subduction zone (Hellenic subduction zone) and Hellenic subduction zone was defined with the foci depth data (USGS) along the south-north direction. Thus, geometry of the focal depth distribution has been created to determine probable media depths and their localizations. According to the NFG results, vertical structural transitions were observed at a depth ranging between 10 and 180 km. Also, these results were compared with the foci depth model and the other results of the related publications. Finally, some considerations in vertical solution with the NFG method have been presented and locations of the different structures at horizontally have been defined with application of the NFG method