Halil İbRahim Solak

Postseismic deformation provides fundamental insights into earthquake-cycle processes, lithospheric rheology, and stress redistribution following large earthquakes. Although the 2020 Mw 7.0 Samos earthquake has been extensively investigated in terms of coseismic deformation and early postseismic behavior, the long-term evolution of deformation following the event remains poorly constrained. This study characterizes the long-term spatiotemporal evolution of postseismic deformation associated with the 2020 Mw 7.0 Samos earthquake using combined campaign and continuous GNSS observations. A total of 18 GNSS stations were analyzed over an approximately 4.5-year period following the earthquake. Pre-earthquake GNSS velocities were incorporated as prior constraints, while postseismic deformation was modeled using linear, logarithmic, exponential, and combined logarithmic–exponential functions. The preferred model for each station component was identified using the corrected Akaike Information Criterion (AICc), and model-selection robustness was evaluated through 1000 Monte Carlo observation–perturbation simulations. The results reveal a spatially heterogeneous postseismic deformation field with station-dependent temporal behavior. Among the nonlinear solutions passing the Monte Carlo and goodness-of-fit criteria, the seven single-process LOG and EXP solutions yielded characteristic relaxation times ranging from 182.6 to 730.5 days, with a median of 438.3 days. The two LOGEXP solutions additionally contained a logarithmic timescale of 109.6 days and exponential timescales of 292.2–438.3 days. These findings demonstrate that campaign GNSS observations, when integrated with continuous GNSS data and an objective statistical framework, can provide meaningful constraints on the long-term evolution of postseismic deformation despite sparse temporal sampling. More broadly, the results emphasize the strongly time-dependent nature of postseismic deformation and the critical role of observation timing in capturing its spatiotemporal evolution.

Batı Anadolu, küresel ölçekte en hızlı genişleyen kıtasal bölgelerden biri olarak kabul edilmekte olup, Akşehir-Simav Fay Sistemi (ASFS) bu rejim içindeki sismik açıdan en aktif yapılardan birisidir. ASFS’nin kuzeybatı bölümünü temsil eden Simav Fay Zonu’nun segmentlerinden birisi olan Banaz Fayı (BF); yapısal haritalama, 11 lokasyondan elde edilen 155 fay çiziği verisinin paleogerilme analizi ve jeodezik veriler ışığında yeniden değerlendirilmiştir. Yaklaşık 37 km uzunluğundaki Banaz Fayı; Gürlek, Kızılcaören ve Derbent olarak adlandırılan üç farklı segmentten oluşan karmaşık bir yapı olarak tanımlanmıştır. Paleogerilme analizleri, yerel gerilme alanında belirgin mekânsal ve zamansal değişimler olduğunu göstermektedir. Kuzeybatıdaki Gürlek segmenti, yataya yakın σ1 ekseni altında baskın sağ yanal doğrultu atımlı bir karakter sunar. Güneydoğuya doğru fay kavislenerek Kızılcaören ve Derbent segmentlerine geçiş yapmakta, burada σ1 ekseninin düşey konuma gelmesiyle mekanizma normal/oblik faylanmaya dönüşmektedir. Evrendede mevkiindeki birbirini üzerleyen kayma çizikleri, saf normal faylanmadan sağ yanal ve normal bileşenli oblik faylanmaya doğru bir geçişi ve σ3 ekseninin zamanla saat yönünün tersine döndüğünü kanıtlamaktadır. Jeolojik ve morfotektonik analizler, Pliyo-Kuvaterner'den bu yana yaklaşık 0,1 mm/yıl düşey kayma hızı göstermekte olup bu değer güncel GNSS gerinim hızları (1-2 mm/yıl) ile uyumludur. Fay doğrultularına (K55°B ve K40°D) paralel gelişen sırt tipi travertenler, fayın güncel aktivitesine işaret etmektedir. Sismik tehlike analizleri, segmentlerin tek tek kırılması durumunda Mw 6,12 – 6,56 aralığında, tüm zonun eş zamanlı olarak kırılması durumunda ise Mw 6,9 büyüklüğünde bir deprem üretme potansiyeli bulunduğunu ortaya koymaktadır. Sonuç olarak bu çalışma; genişlemeli rejimlerdeki atkuyruğu yapılarının üst üste binen farklı genişleme evreleri, segmentasyon kontrolü, sistematik atım dağılımı ve dinamik lokal gerilme değişimleri ile (eksen rotasyonları) geliştiğini; bu mekanizmaların ise derin hidrotermal akışkan yollarını doğrudan kontrol ettiğini ortaya koymaktadır.

In recent years, the rapidly advancing Light Detection and Ranging (LiDAR) technology has become an important tool in geosciences, particularly in paleoseismology, due to its ability to provide highly accurate topographic data. In this study, trench-based paleoseismological investigations were conducted at two different locations along the Gelenbe Fault Zone within the İzmir–Balıkesir Transfer Zone (İBTZ), as part of the project titled “Determination of the Paleoseismological Characteristics of Active Faults in Turkey” (Project No: 123G020). Gelenbe Fault Zone is a right-lateral strike-slip fault extending approximately in a NNE–SSW direction between Bigadiç (Balıkesir) and Akhisar (Manisa). Within the zone, the East and West Segments, measuring 35 km and 36 km in length respectively, are approximately parallel to each other. Within the scope of the study, the trench walls excavated across the fault were cleaned, gridded at one-meter intervals, and subsequently scanned using LiDAR technology to obtain high-resolution data. The acquired point clouds were integrated with photogrammetric data and modeled in three dimensions using Agisoft Metashape Professional and CloudCompare software. To evaluate the geometric accuracy of the model, the one-meter grids marked on the trench walls were used as reference points, and the root mean square error was calculated. The analyses revealed that the model’s accuracy value was ±17 mm, consistent with results obtained by similar methods in the literature. To determine the impact of this spatial error on seismotectonic interpretations, different displacement scenarios were tested, and the results demonstrated that the ±17 mm model error caused a negligible deviation of only ±0.02 magnitude in the calculated moment magnitudes. These findings demonstrate the applicability of LiDAR technology for producing high-accuracy Three-Dimensional models in paleoseismological studies and provide a valuable example for preserving refilled trenches as permanent digital archives

The North Anatolian Fault Zone (NAFZ) in the north of Türkiye is considered one of the most active faults on earth and have caused many major earthquakes in the last century. Surface ruptures by those earthquakes indicate that this tectonic feature consists of many segments, which reveal different characteristics in terms of geometry and mechanism. NAFZ lies along between Bingöl in the eastern Turkey and Saros Gulf in the west. This study focuses on the central part of the NAFZ between Niksar and Ilgaz provinces. In addition to the main branch, the central section of the NAFZ also contains two sub-branches extending southward: Merzifon-Esençay and Sungurlu Faults. In the literature, there are several studies for the region, however a comprehensive study mainly focusing on the main branch of the NAFZ and its sub-branches along the central NAFZ has not been conducted yet, which would fully reveal the fault mechanism and seismic potential in the region. The aim of this study is to derive an up-to-date high-spa-tial-resolution Global Navigation Satellite Systems (GNSS) velocity field for the central NAFZ and to correlate with the strain accumulations along the faults. Based on this, a high-spatial-resolution GNSS network consisting of 60 sites was established enclosing the central NAFZ. The previously archived GNSS data for the same observation sites were collected from the different studies in the region and a new GNSS campaign measurement was conducted between October 2023 and February 2024. All GNSS data were processed using GAMIT/GLOBK software, and the results indicate the GNSS velocities ranging from 3-30 mm/year and their associated uncertainties of maximum ± 1.5 mm/year with respect to the Eurasian tectonic plate.

GNSS-derived strain-rate analysis, geodetic earthquake recurrence modeling, and seismic potential estimations were integrated to investigate segment-scale deformation behavior along the central North Anatolian Fault Zone (NAFZ) using a high-resolution geodetic velocity field. The obtained strain rates reveal that deformation within the central NAFZ is distributed across a geometrically complex and kinematically heterogeneous fault network rather than being restricted to the main fault strand alone. While the main fault accommodates the majority of regional deformation, significant strain accumulation is also observed along major splay fault systems, including the Merzifon–Esençay, Ezinepazarı, Sungurlu, Eldivan, and Ekinveren faults. The derived strain patterns further indicate the coexistence of localized transtensional and transpressional deformation regimes controlled by fault geometry, segment boundaries, and structural discontinuities. Geodetically derived earthquake recurrence periods display pronounced spatial variability, with shorter recurrence periods concentrated along the main fault strand and comparatively longer earthquake cycles characterizing structurally complex splay systems. Among the investigated structures, the eastern and central segments of the Merzifon–Esençay Fault (MEF) exhibit relatively elevated strain accumulation and seismic potential. In particular, the estimated potential earthquake magnitudes reaching Mw 7.3–7.5, together with paleoseismological evidence indicating that the most recent major surface-rupturing event along the Esençay segment occurred approximately 3700 years ago, suggest that this fault system may represent a candidate seismic gap within the central NAFZ. Overall, the results demonstrate that deformation within the central NAFZ is strongly partitioned among interacting fault segments and highlight the importance of segment-scale geodetic analyses for improving seismic hazard assessments in complex strike-slip fault systems.

The Sındırgı region of western Anatolia, located within the extensional tectonic regime of Türkiye, experienced two moderate earthquakes in 2025, occurring on 10 August (Mw 6.1) and 27 October (Mw 6.1). In this study, high-rate (1 Hz) Global Navigation Satellite System (GNSS) observations were analysed to estimate earthquake magnitudes using peak ground displacement (PGD) measurements. GNSS data from 10 stations for the August event and 12 stations for the October event were processed using the PRIDE PPP-AR software to derive displacement time series. Earthquake magnitudes were estimated from PGD values using empirical relationships proposed in previous studies. Overall, the GNSS-based magnitude estimates show good agreement with values reported in seismic catalogues, ranging between Mw ≈ 5.5 and 6.1, with one of the evaluated empirical PGD–Mw relationships providing the closest agreement (Mw = 6.07 ± 0.3 and Mw = 6.13 ± 0.2, respectively). In addition, a strong consistency was observed between GNSS-derived PGD onset times and S-wave arrival times recorded at seismometer stations, particularly within 10–50 km of the epicentre, demonstrating the capability of GNSS observations to reliably capture both coseismic displacement and seismic-wave propagation characteristics. Furthermore, the observed consistency between co-located low-cost and geodetic-grade GNSS receivers highlights the potential of low-cost GNSS systems for reliable coseismic deformation monitoring and for the development of dense GNSS observation networks.

The Caucasus region represents the northern edge of the Arabia–Eurasia continental collision and accommodates complex deformation involving crustal shortening, lateral block motion, and strike-slip faulting across multiple tectonic domains, including the Greater and Lesser Caucasus, the Kura Basin, and northwestern Iran block. Despite its tectonic significance, the spatial partitioning of present-day deformation and the role of vertical motions were not completely resolved. In this study, we present a comprehensive geodetic analysis of active deformation across Azerbaijan and the surrounding Caucasus region based on long-term continuous GNSS observations. Ten years (2014–2023) of data from 24 permanent GNSS stations were processed to derive a consistent Eurasia-fixed velocity field. To enhance spatial resolution, these new velocities were integrated with previously published regional GNSS solutions using a common reference frame and transformation strategy, resulting in a unified and unprecedented velocity field of 131 GNSS sites. Strain rates were estimated from the combined velocity field, and fault slip rates and block rotations were quantified through elastic block modeling. The horizontal velocity field indicates N-NE motion of ~ 12 mm/yr relative to Eurasia, with pronounced eastward rotation and velocity increase toward the Caspian margin. Vertical deformation at regional scale with high accuracy, revealing coherent uplift of ~ 4–5 mm/yr along the Greater Caucasus. Apart from the highest spatial resolution of deformation with 131 GNSS sites in the region, the sufficiently accurate vertical deformation rates are presented for the first time in the region through 24 permanent GNSS stations. Strain-rate and block modeling results demonstrate strong deformation partitioning, with thrust-dominated shortening concentrated along the Greater Caucasus and right-lateral strike-slip motion accommodating eastward escape along major fault systems. These results provide refined constraints on the kinematics of the Arabia–Eurasia collision in the Caucasus and offer important implications for regional tectonic evolution and seismic hazard assessment. Graphic abstract

This study presents a new high-resolution GNSS-derived velocity field and the first internally consistent, segment-resolved block model for the Havran–Balıkesir Fault Zone (HBFZ) in western Anatolia. Inversion of the GNSS velocity field was performed using a dense network of 77 sites within a 3D elastic half-space framework to estimate fault slip rates and interseismic coupling. The results reveal that the HBFZ behaves as a kinematically heterogeneous fault system, with deformation systematically partitioned along strike. Block-modeling results indicate pronounced along-strike variations in interseismic coupling and slip-deficit accumulation. While the westernmost Havran segment is weakly coupled and accommodates limited accumulation, the Turplu and Gökçeyazı segments emerge as major strain-accumulation zones with high and laterally continuous slip-deficit rates. In particular, the Gökçeyazı segment exhibits slip-deficit rates of ~4–6 mm/yr and nearly two millennia of seismic quiescence, implying the potential for a future large-magnitude earthquake (Mw ~7.1–7.3). The strong agreement between GNSS-derived deformation patterns and independent geological and paleoseismological constraints suggests that this segment is currently in an advanced stage of the seismic cycle. These findings highlight the importance of segment-scale geodetic observations for seismic hazard assessment in northwestern Anatolia.

Bu çalışmada, 2023 Kahramanmaraş depremleri (Mw:7.7 Pazarcık ve Mw:7.6 Ekinözü) sonrası Kuzeydoğu Anadolu Fay Zonu üzerinde bulunan Erzurum ve çevresindeki kosismik yer değiştirmelerin hesaplanması amacıyla 22.FENBIL.30 no’lu proje kapsamında kurulan 17 noktalı GNSS ağı kullanılmıştır. Ağda yer alan noktalarda 2022 ve 2023 yıllarında gerçekleştirilen GNSS ölçümlerinden elde edilen koordinatlar, bölgede yer alan TUSAGA-Aktif istasyonları ve TUTGA-99A noktalarının intersismik ve postsismik hızları kullanılarak deprem epoğuna taşınmıştır. Elde edilen sonuçlar Kahramanmaraş depremleri kaynaklı kosismik yer değiştirmelerin Erzurum civarında vektörel olarak 2.5 mm ile 30 mm arasında olduğunu ve bölgede GB yönlü bir atımın meydana geldiğini göstermektedir. Bu sonuçlar, sol yanal atım karakterine sahip fayların ürettiği bu yıkıcı depremlerin dış merkezleri ve odak mekanizma çözümleri ile literatürde gerçekleştirilen geniş ölçekli çalışmalarla uyum içerisindedir. Ayrıca, Erzurum ve çevresindeki mevcut sismik tehlikeyi değerlendirmek amacıyla 1900-2024 yılları arasını kapsayan KRDAE deprem kataloğu kullanılarak hesaplanan a ve b parametreleri, 3 ayrı alt bölgeye ayrılan alanda bulunan faylarda farklı aktivite ve gerilim birikim düzeyleri olduğunu göstermiştir. Hesaplamalar sonucunda a parametresi, Erzurum’un B-KB’sındaki bölgede yüksek (a=5.29), diğer bölgelerde ise orta seviyede sismik aktiviteyi işaret etmektedir. b parametresi ise Erzurum’un batısında küçük depremlerin daha sık olduğunu (b=0.90), doğusunu kapsayan bölgede büyük depremlerin daha fazla olabileceğini (b=0.69), güneyinde ise daha dengeli bir tehlike profili olduğunu ortaya koymuştur (b=0.76). Elde edilen sonuçlar, bölgenin sismik aktivitesiyle uyumlu olup, bölgedeki heterojen tektonik yapıların büyük deprem potansiyeli taşıdığını göstermektedir. Bu bulgular, bölgedeki gelecekteki deprem tehlike analizleri için önemli bir temel oluşturmaktadır.