Orta Anadolu’nun kabuksal hız yapısının araştırılması

Öz

Bu çalışmada Orta Anadolu altında kabuk ve üst-manto hız yapısının tespiti için P dalgası alıcı fonksiyon analizi kullanılmıştır. Bu amaçla Bayındırlık ve İskân Bakanlığı Afet İşleri Genel Müdürlüğü, Deprem Araştırma Daire Başkanlığı bünyesinde aktif olarak çalıştırılan geniş-bantlı ANTO (Ankara), BBAL (Ankara), CDAG (Kırşehir), ELDT (Çankırı) ve ILGA (Çankırı) deprem istasyonlarında kaydedilen telesismik depremlerin zaman ortamı P alıcı fonksiyonları hesaplanmıştır. Ayrıca bölgesel yüzey dalgası grup hızı bilgileri ile her deprem istasyonunda hesaplanan radyal alıcı fonksiyon sinyalleri birlikte ağırlıklı ters çözülerek çok çözümlülük sorunu da giderilmiştir. Ters çözüm sonuçlarından ANTO istasyonu altında kabuksal kalınlık 36 km ve makaslama hızı 4.33 km/sn, BBAL istasyonu altında kabuksal kalınlık 38 km ve makaslama hızı 4.28 km/sn, CDAG istasyonu altında kabuksal kalınlık 40 km ve makaslama hızı 4.33 km/sn, ELDT istasyonu altında kabuksal kalınlık 36 km ve makaslama hızı 4.21 km/sn, ILGA istasyonu altında kabuksal kalınlık 36 km ve makaslama hızı 4.20 km/sn elde edilmiştir. Bu durum Orta Anadolu’da kuzeyden güneye doğru bir kabuksal kalınlaşmanın olduğunu gösterir. Bölgenin tektonik bakımdan Ezinepazarı-Tuz Gölü Fayı, Ecemiş Fayı, Kırıkkale-Erbaa Fayı ve kuzeyden İzmir-Ankara-Erzincan ile güneyden Toroslar’ın paleosütur kuşaklarının sıkıştırma etkisi altında olması, güneydeki bu kabuksal kalınlık artışının nedenidir. İstasyonlar altında üst-kabuk makaslama hızları 2.20-3.49 km/sn arasında değişmektedir ve üst-manto hızı

Anahtar Kelimeler

• Alıcı fonksiyon, kabuk hız yapısı, Orta Anadolu, ters çözüm, yüzey dalgası.

Investigation of the crustal velocity structures in the Central Anatolia

Öz

Studying area is located in Central Anatolia, surrounded by the locations of Pontides to the northnorthwest and Anatolides to the south. Fundamental tectonic structures of the area are namely North Anatolian Fault Zone, Kırıkkale-Erbaa Fault Zone, Eldivan-Elmadağ Pinched Wedge, Ezinepazarı-Tuz Gölü Fault Zone. In this study, P receiver function analysis is used to estimate the crustal and the upper mantle velocity structures beneath the Central Anatolia. To reach this goal, time domain P receiver of teleseismic events are computed, which are recorded by a total number of 5 broad-band stations, namely ANTO (Ankara), BBAL (Ankara), CDAG (Kırşehir), ELDT (Çankırı) and ILGA (Çankırı) which belong to actively operating General Directorate of Disaster Affairs, Earthquake Research Department, Seismology Division of Ankara. Moreover, computed radial receiver functions and regional surface wave group velocities are inverted as weighted in each individual earthquake station; thus, non-uniqueness problem is solved. Receiver function analysis is operated helping with the digital three component earthquake records, are higher than 20° epicentral distance. Time domain deconvolution technique is applied in this study, intends to acquire the source-time function of complex body waves from deconvolution of synthetic seismograms, obtained from observational wave forms. Radial and tangential receiver functions are initially computed for each determinated earthquake. In order to applicate the technique; before 10 s and after 90 s, first P arrival is selected as 100 s, for three component. Horizontal components of selected signals (N-S and E-W) are converted theoretical radial and tangential components considering backazimuth values. Observational vertical component seismogram is distinguished from radial and tangential component seismograms by use of deconvolution; hence, radial and tangential component receiver function signals are computed. Computed radial and tangential receiver functions ranged as back-azimuths and placed in backazimuth-epicentral distance projection. Earthquakes in each station, are grouped in accordance with the back-azimuth and the epicentral distance classification. It is totally analysed 21 groups in 5 stations. Computed radial receiver functions and regional surface wave group velocities are inverted as weighted in each individual earthquake station; thus, non-uniqueness problem is solved. Inversion results show that crustal thicknesses and shear velocities beneath the stations ANTO, BBAL, CDAG, ELDT, ILGA are stated 36 km, 4.33 km/s; 38 km, 4.28 km/s; 40 km, 4.33 km/s; 36 km, 4.21 km/s and 36 km, 4.20 km/s, respectively. This result indicates that crustal thickening is present from the north to the south. The reason of rising crustal thickening to south is that the area is compressed by paleosutures of Toroids from south and of IzmirAnkara-Erzincan from north and Ezinepazarı-Tuz Gölü Fault, Ecemiş Fault, Kırıkkale-Erbaa Fault tectonically. Upper-mantle shear velocities vary from 2.20 to 3.49 km/s beneath the stations and upper-mantle velocity is lower than 7.8 km/s. No abnormal low velocity zone (LVZ) at middle-crust and upper-crust is observed. Shear velocity changes are approached up to 60 km beneath the each station. Inversion results will dissipate lack of priori information and provide substantial contribution of neotectonic interpretation in the region.

Anahtar Kelimeler

• Central Anatolia, crustal velocity structure, inversion, receiver function, surface wave.