Comprehensive SKS Polarization Analyses in the Marmara Region and Implications for the Upper Mantle Deformation

In the present study, deformation pattern within the upper mantle part beneath the Marmara region was investigated using SKS phases observed on the waveform recordings of teleseismic events. 572 good-quality SKS splitting measurements observed at 34 seismic stations, assuming a single-layer anisotropy, resulted in splitting time delays (TD) between fast and slow S-waves ranging from 0.97 s to 2.17 s. Station-averaged fast polarization directions exhibits an overall NE-SW oriented distribution. They vary between N10°E and N63°E. Staion-averaged splitting measurements are in a good accordance with those obtained at various parts of Anatolia as this implies observed seismic anisotropy beneath the Marmara region is likely due to the mantle convection flow and associated lattice preferred orientation (LPO) that have been developed by the roll-back effect of subducting African plate beneath the Anatolia along the Hellenic Trench. Two-layer anisotropy modeling results inferred from directional dependency of apparent SKS splitting parameters tend to support this result. Comparison of the findings from present study with those from local S-wave splitting-derived upper crust (8-10 km) anisotropy results suggest that there is no a vertical coherency in transmitting the deformation from the crust to lithosphere and upper mantle in the study area.Bu çalışmada, telesismik (uzak) depremlere ait dalga formu kayıtları üzerinde gözlenen SKS fazı kullanılarak Marmara Bölgesi’nin altında kalan manto yapısının deformasyonu ile ilişkili anizotropik bulgular incelenmiştir. Bu amaçla kullanılan 34 adet istasyonda, tek-tabakalı anizotropi modeli varsayılarak hesaplanan 572 adet iyi kalitede SKS ayrımlaşması parametresi, hızlı ve yavaş S dalgaları arasındaki zaman gecikmelerinin 0.97 sn ile 2.17 sn aralığında değiştiğini göstermektedir. İstasyon ortalamaları alınarak hesaplanan hızlanma polarizasyonu yönleri K10°D ile K63°D arasında değişerek büyük çoğunlukla KD-GB yönlü bir dağılıma işaret etmektedir. Hesaplanan istasyon ortalaması alınmış zaman gecikmeleri ve hızlanma yönleri, Anadolu için elde edilen ortalama değerlerle benzer bir dağılım gösterir. Bu ise bize, Marmara Bölgesi altında gözlenen sismik anizotropinin, Helenik Yay’ı boyunca Anadolu kıtası altına dalım yapan Afrika levhasının geriye çekme etkisi sonucu şekillenen manto konveksiyon akımları ve buna bağlı gelişen kafes tipi tercihi yönelim (LPO) ile ilişkili olduğunu göstermektedir. Buna ek olarak, SKS ayrışma parametrelerinin yönsel değişimleri üzerine uygulanan ikitabakalı anizotropik yapı modellemeleri bu sonucu destekler niteliktedir. Bu çalışmadan elde edilen bulgular, Marmara Bölgesi için önceki yıllarda lokal S dalgaları kullanılarak gözlemlenmiş üst-kabuk (8-10 km) anizotropisi ile kıyaslandığında, deformasyonun düşey yönde kabuktan litosfer boyunca üst mantoya kadar sürekli bir şekilde iletilmediğini göstermektedir

Localized crustal deformation along the central North Anatolian Fault Zone revealed by joint inversion of P-receiver functions and P-wave polarizations

The North Anatolian Fault Zone (NAFZ) is a major plate boundary that separates the Eurasian Plate to the north from the Anatolian Plate to the south and is associated with powerful damaging earthquakes. Despite numerous studies of the crust and upper mantle across the NAFZ, our understanding of the exact mechanisms and distribution of deformation with depth is still limited. Accurate models of the crustal velocity structure are key to assess seismic hazard associated with strike-slip deformation. Here, we address this need by employing a novel method that jointly inverts receiver function waveforms and P-wave polarizations to recover S-wave velocity structure from the surface to the upper mantle. The method is applied to a dense teleseismic data set collected across a segment of the central NAFZ in Turkey. The results provide important new constraints on the sedimentary thickness, depth to basement and Moho discontinuity beneath the region. Our estimates of uppermost sedimentary thickness range from 0 km in some areas (e.g. in the Central Pontides) to 6 km in the Çankırı Basin. Smaller basins are scattered along the NAFZ. A similar pattern is observed for the basement depth, with values exceeding 10 km beneath the Çankırı Basin, where the Moho is shallowest with a depth of ∼32 km. The Moho reaches a maximum depth of ∼42 km beneath the Central Pontides. Most other areas have an average Moho depth of 35–38 km. The results reveal clear structural–tectonic relationships in the crust: areas of fundamentally different sedimentary and crustal architecture are bounded by faults and suture zones. The NAFZ appears to accommodate small-scale basin and basement-highs, and acts as a thick-skinned (i.e. full crustal-scale) boundary between laterally displaced crustal blocks to the north and south. Seismicity clusters are centred on areas of low Vp/Vs ratios that may be representative of weak zones.publishedVersio

Fault-model of the 2017 Kos-Bodrum (east Aegean Sea) Mw 6.6 earthquake from inversion of seismological and GPS data – Preliminary Report

The 20 July 2017 Kos-Bodrum Mw 6.6 normal fault earthquake (AFAD, 2017) at the NW edge of the Quaternary Gökova Bay graben, was a destructive earthquake associated with a small tsunami (Yalciner et al., 2017). In addition, it is the first normal faulting earthquake in the Aegean covered by a dense array of continuous GPS stations which permit a detailed finite fault modeling (FFM). The preliminary seismological evidence (epicenters, hypocenters of the main shock and of the main aftershocks, and focal mechanism of the main shock) deriving from various agencies, data and techniques, indicate a shallow, nearly E-W striking normal faulting, but its details, including its dip (northerly or southerly) are not resolved. On the basis of independent analysis of seismological and geodetic data we obtained Finite Fault Models (FFM), which are very similar and hence describe the “true” fault

Geodetic and seismological analysis of the 2017 Kos-Bodrum Mw 6.5 earthquake (SE Aegean Sea) provides evidence for the evolution of normal faulting in Gökova graben

The epicentral area of the 2017, Mw 6.5 destructive Kos-Bodrum normal faulting earthquake, associated with a small tsunami in a touristic region, is located within the active Gökova graben and represents a case of a previously unrecognized, shallow normal fault without clear geomorphological signature. Analysis of teleseismic body-waveform data and geodetic data, both in the near- and far- field, indicate a well-constrained 25km long and 10km deep south-dipping normal fault which produced small uplift in the Bodrum peninsula. Modeled fault marks the NW edge of the actively extending part of the Gökova graben and was associated with two clusters of aftershocks, while only its eastern part correlates with known active faults. The 2017 earthquake seems to reflect an immature normal fault between Kos Island and the Anatolia mainland, and expansion of the Gökova graben, perhaps through echelon fractures, as is observed in seismic profiles farther east. Activation of normal faults with modest, if any geomorphic signature, hence not easily recognized before the earthquakes seems not unusual in the Aegean area, and represents a major issue for earthquake hazard analysis

Sub- and super-shear ruptures during the 2023 Mw 7.8 and Mw 7.6 earthquake doublet in SE Türkiye

An earthquake doublet (Mw 7.8 and Mw 7.6) occurred on the East Anatolian Fault Zone (EAFZ) on February 6th, 2023. The events produced significant ground motions and caused major impacts to life and infrastructure throughout SE Türkiye and NW Syria. Here we show the results of earthquake relocations of the first 11 days of aftershocks and rupture models for both events inferred from the kinematic inversion of HR-GNSS and strong motion data considering a multi-fault, 3D geometry. We find that the first event nucleated on a previously unmapped fault before transitioning to the East Anatolian Fault (EAF) rupturing for ~350 km and that the second event ruptured the Sürgü fault for ~160 km. Maximum rupture speeds were estimated to be 3.2 km/s for the Mw 7.8 event. For the Mw 7.6 earthquake, we find super-shear rupture at 4.8 km/s westward but sub-shear eastward rupture at 2.8 km/s. Peak slip for both events were as large as ~8m and ~6m, respectively

Isotropic and Anisotropic P and S Velocities of the Baltic Shield Mantle : Results from Analyses of Teleseismic Body Waves

The upper mantle structure of Swedish part of Baltic Shield with its isotropic and anisotropic seismic velocity characteristics is investigated using telesesismic body waves (i.e. P waves and shear waves) recorded by the Swedish National Seismological Network (SNSN). Nonlinear high-resolution P and SV and SH wave isotropic tomographic inversions reveal velocity perturbations of ± 3 % down to at least 470 km below the network. Separate SV and SV models indicate several consistent major features, many of which are also consistent with P-wave results. A direct cell by cell comparison of SH and SV models reveals velocity differences of up to 4%. Numerical tests show that differences in the two S-wave models can only be partially caused by noise and limited resolution, and some features are attributed to the effect of large scale anisotropy. Shear-wave splitting and P-travel time residual analyses also detect anisotropic mantle structure. Distinct back-azimuth dependence of SKS splitting excludes single-layer anisotropy models with horizontal symmetry axes for the whole region. Joint inversion using both the P and S data reveals 3D self-consistent anisotropic models with well-defined mantle lithospheric domains. These domains of differently oriented anisotropy most probably retain fossil fabric since the domains' origin, supporting the idea of the existence of an early form of plate tectonics during formation of continental cratons already in the Archean. The possible disturbing effects of anisotropy on seismic tomography studies are investigated, and found to be potentially significant. P-wave arrival times were adjusted based on the estimates of mantle anisotropy, and re-inverted. The general pattern of the velocity-perturbation images was similar but changed significantly in some places, including the disappearance of a slab-like structure identified in the inversion with the original data. Thus the analysis demonstrates that anisotropy of quite plausible magnitude can have a significant effect on the tomographic images, and should not be ignored. If, as we believe, our estimates of anisotropy are reasonably correct, then the model based on the adjusted data should give a more robust and correct image of the mantle structure

Extracting, computing, coordination: what does a triphasic ERP pattern say about language processing?

The current study aims at contributing to the interpretation of the most prominent language-related ERP effects, N400 and P600, by investigating how neural responses to congruent and incongruent sentence endings vary, when the language processor processes the full array of the lexico-syntactic content in verbs with three affixes in canonical Turkish sentences. The ERP signals in response to three different violation conditions reveal a similar triphasic (P200/N400/P600) pattern resembling in topography and peak amplitude The P200 wave is interpreted as the extraction of meaning from written.form by generating a code which triggers the computation of neuronal ensembles in the distributed LTM (N400). The P600 potential reflects the widely distributed coordination process of activated neuronal patterns of semantic and morphosyntactic cues by connecting the generated subsets of these patterns and adapting them into the current context. It further can be deduced that these ERP components reflect cognitive rather than linguistic processes. © 2021 Informa UK Limited, trading as Taylor & Francis Group.WOS:000722538700001Scopus - Affiliation ID: 60105072Science Citation Index Expanded - Social Sciences Citation IndexQ1 - Q2Article; Early AccessUluslararası işbirliği ile yapılmayan - HAYIRNovember2021YÖK - 2021-22Kası