Analiza poremećaja ubrzanja sile teže graničnih struktura na području Egejskog mora i Zapadne Anatolije

Western Anatolia has been shaped N–S-trending extensional tectonic regime and W-E trending horst, grabens and active faults due to the collision of Africa, Arabian and Eurasia plates. The borders of the Aegean Sea tectonic is limited between eastern of Greece, western of Anatolia and Hellenic subduction zone in the south of Crete. To evaluate these tectonic elements gravity disturbance data of the Aegean Sea and Western Anatolia was used in this study. It is thought that the gravity disturbance data reflects the tectonic elements and discontinuities way better than gravity anomaly due to the calculation from the difference between gravity and normal gravity at the same point so thus the tensors and invariants of the study area were calculated and the power spectrum method was applied to the gravity disturbance data. Various boundary analysis methods were applied to the gravity disturbance data to compare the discontinuities obtained from the tensors both theoretical and case study. These methods were tested initially on theoretical data. Within the scope of the theoretical study, a single model and three bodies model were taken into consideration. When the results are examined, it is observed that the Tzz tensor component gives very clear information about the location of the structure. Likewise, when the Txx, Tyy components and invariant results are examined, the vertical and horizontal boundaries were successfully obtained. In addition, the mean depths of these structures were determined using the power spectrum method. In the case application stage, the gravity disturbance data obtained from the Earth Gravitational Model of the eastern of the Aegean Sea and western of Anatolia were evaluated. The tensor and invariants of this gravity disturbance data were first calculated. New possible discontinuities have been identified in the tensors and some of the obtained discontinuities were clarified in their previous discussions. Also, the mean depths of the possible structures were calculated by the power spectrum method at four profiles taken from gravity disturbance data. These depth values are consistent with the depth values of the structural discontinuities obtained from previous studies. Finally, the upward continuation was applied to Tyy, Tyz and Tzz tensors up to 20 km. The positive anomaly values in Tyz and Tzz components and negative anomaly values in Tyy component are consistent with the Western Anatolia Transfer Zone. The structural differences between the eastern and the western of Western Anatolia are noteworthy in the upward continued results of the tensors. In addition, the positive and negative anomalies are notable in areas where the big earthquakes occurred in the last 3 years in the Tyz invariants.Zapadna Anatolija je oblikovana u smjeru sjever-jug zahvaljujući ekstenzivnom tektonskom trendu i zapadno-istočnim uzdizanjima, grebenima I aktivnim rasjedima kao posljedicom kolizije Afričke, Arapske i Euroazijske ploče. Granice tektonskog područja Egejskog mora ograničene su između istočne Grčke, zapadne Anatolije i Helenske subdukcijske zone na jugu Krete. Za procjenu tih tektonskih elemenata korišteni su podaci o poremećaju ubrzanja sile teže na području Egejskog mora i Zapadne Anatolije. Smatra se da podaci o poremećaju ubrzanja sile teže odražavaju tektonske elemente i diskontinuitete bolje nego anomalija ubrzanja sile teže zbog računanja razlike između ubrzanja sile teže i normalnog ubrzanja sile teže na istoj točki, tako da su izračunati tenzori i invarijante na promatranom području i metoda spektra snage je primijenjena na podatke poremećaja ubrzanja sile teže. Različite metode analize granica primijenjene su na podatke poremećaja ubrzanja sile teže kako bi se usporedili diskontinuiteti dobiveni iz tenzora. Te su metode najprije ispitane na teoretskim podacima. U okviru teorijske studije uzeti su u obzir jedan samostalni model i tri modela tijela. Prilikom interpretacije rezultata, uočeno je da Tzz tenzorska komponenta daje vrlo jasne informacije o lokaciji strukture. Isto tako, kada se ispitaju Txx, Tyy komponente i nepromjenjivi rezultati, uspješno su dobivene vertikalne i horizontalne granice. Također, srednje dubine tih struktura određene su metodom spektra snage. U stupnju primjene slučaja ispitani su podaci poremećaja ubrzanja sile teže generirani iz Zemljinog gravitacijskog modela EGM na području istočnog Egejskog mora i zapadne Anatolije. Najprije su izračunati tenzor i invarijante poremećaja ubrzanja sile teže. Identificirani su novi mogući diskontinuiteti u tenzorima, a neki od dobivenih diskontinuiteta razjašnjeni su u prethodnim raspravama. Također, prosječne dubine mogućih struktura izračunate su metodom spektra snage na četiri profila iz podataka o poremećaju ubrzanja sile teže. Ove dubinske vrijednosti su u skladu s dubinskim vrijednostima strukturnih diskontinuiteta dobivenih iz prethodnih studija. Naposljetku, kontinuacija prema gore primijenjen je na tenzore Tyy, Tyz i Tzz do 20 km. Vrijednosti pozitivnih anomalija u Tyz i Tzz komponentama i negativne vrijednosti anomalija u Tyy komponenti u skladu su sa transfer zonom Zapadne Anatolije. Strukturne razlike između istočnog i zapadnog dijela Zapadne Anatolije značajne su u daljnjim rezultatima tenzora. Također, pozitivne i negativne anomalije su značajne u područjima gdje su se dogodili veliki potresi u posljednje 3 godine u Tyz invarijantama

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