Abstract Compressional and extensional tectonics following northward plate convergences since the Miocene have formed the major surface features in Turkey, such as faulting and orogeny. Despite increasing efforts in last few decades aiming to elucidate the current architecture of the crust and mantle beneath Turkey, several issues regarding the depth extent of the deformation zones, crust‐mantle interaction (e.g., coupling and decoupling) in relation to the deformation, and stress transmission in the lithosphere remain elusive. Here we present high‐resolution 3‐D P wave isotropic and azimuthal anisotropic velocity models of the crust and uppermost mantle beneath Turkey by inverting 204,531 P wave arrival times of 8,103 local crustal earthquakes. Our results reveal low‐velocity anomalies or velocity contrasts down to the uppermost mantle along the North and East Anatolian Fault Zones. The fast velocity directions (FVDs) of azimuthal anisotropy in the lower crust and uppermost mantle are parallel to the regional maximum extensional directions in western Turkey, and the FVDs in the crust and uppermost mantle are parallel to the surface structures in southeastern Turkey. These results indicate that vertically coherent deformation between the crust and uppermost mantle occurs in western and southeastern Turkey. However, in central northern Turkey, the FVDs in the uppermost mantle are oblique to both the FVDs in the lower crust and the maximum shear directions derived from GPS measurements, suggesting that the crust and lithospheric mantle are decoupled there.
The eastern Mediterranean which is one of the most tectonically active collisional regions where Eurasian, African and Arabian plates converge, provides an excellent opportunity to investigate the evolution of various scales of deformation throughout the Earth. In such a region with highly complex and active tectonic structures, a detailed study of geodynamic processes and related mantle kinematics is required to better understand the development of complex structures at the surface. For example, the region of study, the Anatolian plate and surroundings host several complicated deformation regimes with two large transform faults (North and East Anatolian Faults; NAF and EAF, respectively), regions of extensional and compressional tectonics in the west and east of Anatolia. Seismic anisotropy provides a robust link between seismic observations and geodynamic processes which play a key role for controlling the past and/or present deformations in the mantle lithosphere and asthenosphere. In this study, we perform shear wave splitting analyses on teleseismic core-refracted S-waves (e.g. SKS and SKKS phases) recorded by ~600 broad-band seismic stations located in the region. We estimate seismic anisotropy parameters (e.g., fast polarization direction; FPD and delay time; DT) beneath each seismic station by employing conventional shear wave splitting (e.g., transverse energy minimization and eigenvalue) and splitting intensity approaches. Exploiting a large earthquake dataset, spanning through 2000-2022 with Mw ≥ 5.5 events, that covers a wide range of back-azimuths enables the reliable estimates of complex anisotropic models, such as two-layer and dipping anisotropy models. Our preliminary results largely indicate the NE-SW directed FPDs throughout the study area, except for SW Turkey (NW-SE) and central parts of Anatolia (E-W) that can be mainly explained by the lattice-preferred orientation (LPO) of olivine minerals in the upper mantle induced by the mantle flow related to the roll-back process of the Hellenic slab. Findings from our two-layer grid search algorithm indicated strong evidences for two-layer anisotropy models beneath the seismic stations in eastern Aegean and western Anatolia, in particular close to the western branches of NAF in the Aegean.
<p>Seismic anisotropy studies can provide important constraints on geodynamic processes and deformation styles in the upper mantle of tectonically active regions. Seismic anisotropy parameters (e.g. delay time and fast polarization direction) can give hints at the past and recent deformations and can be most conventionally obtained through core-mantle refracted SKS phase splitting measurements. In order to explore the complexity of anisotropic structures in the upper mantle of a large part of the Aegean region, in this study, we estimate splitting parameters beneath 25 broad-band seismic stations located at NW Anatolia, North Aegean Sea and Greece mainland. To achieve this we employ both transverse energy minimization and eigenvalue methods. Waveform data of selected earthquakes (with M<sub>w</sub> &#8805; 5.5; 2008-2018 and with epicentral distances between 85&#176;&#8211;120&#176;) were retrieved from Earthquake Data Center System of Turkey (AFAD; http://tdvm.afad.gov.tr/) and European Integrated Data Archive (EIDA; http://orfeus-eu.org/webdc3/). A quite large data set, the majority of which have not been studied before, were evaluated in order to estimate reliable non-null and null results. In general, station-averaged splitting parameters mainly exhibit the NE-SW directed fast polarization directions throughout the study area. These directions can be explained by the lattice-preferred orientation of olivine minerals in the upper mantle induced by the mantle flow related to the roll-back process of the Hellenic slab. We further observe that station-averaged splitting time delays are prone to decrease from north to south of the Aegean region probably changing geometry of mantle wedge with a strong effect on&#160; the nature of mantle flow along this direction. The uniform distribution of splitting parameters as a function of back-azimuths of earthquakes refers to a single-layer horizontal anisotropy for the most part of the study area. However, back azimuthal variations of splitting parameters beneath most of northerly located seismic stations (e.g., GELI, SMTH etc.) imply the presence of a double-layer anisotropy. To evaluate this, we performed various synthetic tests especially beneath the northern part of study region. Yet, it still remains controversial issue due to the large azimuthal gap and thus requires further modelling which may involve the use of joint data sets.</p>
After the 1999 Izmit and Duzce earthquakes, the multi-method SEISMARMARA seismic survey has been carried out with the aim to constrain the seismogenic part of the North Anatolian Fault (NAF) immersed into the Marmara Sea. During this survey, a network of 35 3-components Japanese Ocean Bottom Seismometers (OBS) placed on a 2D grid and land stations have recorded the current seismic activity for a period of 6 weeks and 2000 km of MCS profiles shot in the North Marmara Trough (NMT).
Gokova Korfezi Turkiye’nin guneybatisinda Ege Denizi kiyisinda yer alan ve bolgedeki tektonik ve depremsellik acisindan aktif graben sistemlerinden biridir. Son yillarda ozellikle 2004-2005 tarihleri arasinda korfez icerisinde bir cok sayida orta buyuklukte (M w ³ 5.0) deprem meydana gelmistir. Bu calismada ters cozum teknikleri ve telesismik uzakliklarda kaydedilen P ve SH dalga sekilleri kullanilarak bolgede olusan guncel depremlerin kaynak mekanizmasi parametreleri ve fay duzlemi uzerinde meydana getirdikleri kayma dagilimi ve yirtilma surecleri modelleri elde edilmistir. En kucuk hatali kaynak mekanizmasi cozumlerine gore depremler genel olarak D-B dogrultulu normal faylanma mekanizmasi ile sig odak derinliklerinde meydana gelmektedirler. Kaynak mekanizmasi cozumlerinde cok kucuk miktarlarda dogrultu atimli faylanma bilesenleri bulunmaktadir. Telesismik cisim dalgalarinin ve yakin alan istasyonlarin ters cozum ile modellenmesi sonucu elde edilen kayma dagilimi modelleri ise depremlerin oldukca basit sekilli ve dalim yonunde ilerleyen dairesel kirilmalar ile meydana geldiklerini gostermektedir. Ayrica, Hellenik Yayi’nin dogu uzanimi uzerinde yer alan Rodos adasi ve cevresinde tarihsel donem icerisinde meydana gelen ve tsunami (depresim) dalgalarina neden oldugu rapor edilen bircok sayida deprem bulunmaktadir. 1481 yilinda meydana gelen tarihsel depremler icin sig su dalgasi teorisine dayali yontemlerle ve GEBCO-BODC batimetri verisi ile tsunami dalga simulasyonlari yapilmistir. Simulasyon sonuclari bu bolgede meydana gelen bir depremin daha cok episantira yakin bolgelerde ornegin Rodos adasi ve cevresinde ve Gokova Korfezi - Fethiye kiyilarinda etkili tsunami dalgalarina neden oldugunu gostermektedir. Anahtar Kelimeler: Anadolu , deprem, Gokova Korfezi, Rodos-Dalaman, sismotektonik, tsunami.
