Orta Anadolu’nun kabuksal hız yapısının araştırılması

Year 2010, Volume: 1 Issue: 1, 49 - 60, 01.06.2010

Aytek Ersan , Murat Erduran

Abstract

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

Keywords

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

Investigation of the crustal velocity structures in the Central Anatolia

Abstract

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.

Keywords

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