Cemal Ozer Yigit

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.

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.

With the advancement of GNSS data processing strategies and the availability of data at 20 Hz sampling rate or higher, GNSS has become an essential and effective method for monitoring dynamic defor...

In the last few decades, GNSS observations have frequently been used in Structural Health Monitoring (SHM) and Earthquake Early Warning (EEW) systems. The primary advantage of high-frequency GNSS techniques is to detect displacements directly in a terrestrial reference frame compared to conventional geotechnical sensors. Among GNSS techniques, the real-time kinematic (RTK) has predominantly been employed in dynamic displacement monitoring because it provides high accuracy simultaneously. Nevertheless, an external GNSS infrastructure is essential in RTK applications to achieve high positioning accuracy, which restricts its use in possible mega earthquake events. On the other hand, Precise Point Positioning (PPP), which can provide high positioning accuracy with a standalone GNSS receiver on a global scale, emerged as an alternative to traditional GNSS techniques. However, the requirement of an external internet connection for real-time PPP applications is the main restriction of this technique in the employment of possible mega earthquake events like the RTK technique. Instead, the variometric approach (VA) can provide high accuracy in determining dynamic behaviors with a standalone GNSS receiver and broadcast ephemeris only, which means it doesn't require any external infrastructure and connection. Furthermore, the emergence of new navigation systems, such as Galileo and BeiDou, brings considerable opportunities to improve the performance of the VA technique in detecting dynamic behaviors. Thanks to progress in GNSS receiver technology, low-cost GNSS receivers have been introduced and taken considerable attention from the GNSS community. Their more compact design makes low-cost GNSS receivers very usable for establishing monitoring networks in harsh environments, such as high-rise buildings and bridges. In this context, this study aims to evaluate the capability of the VA technique with a low-cost GNSS receiver in detecting horizontal dynamic motion simultaneously. For this purpose, this study employs single-frequency (SF) observations of GPS, GLONASS, Galileo, and BeiDou satellites from the u-blox ZED-F9P receiver for the VA technique. Harmonic motions from 5 to 20 mm with frequencies between 0.3 and 5.0 Hz were generated by a single-axis shake table to analyze the capability of the SF-VA technique in detecting structural motion. Also, a simulation of Mw 6.9 Kobe, 1995 earthquake was performed using the shake table to understand the feasibility of the SF-VA technique in possible EEW systems. In the evaluation, displacements from the Linear Variable Differential Transformer (LVDT) were selected as the reference to assess the capability of the SF-VA technique. The results indicated that the peak frequency value of short-term harmonic oscillations up to 5 Hz can be detected with the SF-VA technique adopting GNSS observations from the low-cost receiver. Besides, the results demonstrated that the SF-VA technique can determine the strong ground motions resulting from mega earthquakes at mm-level.

30 Ekim 2020 tarihinde Sisam adası kuzeyinde Mw:6.9 büyüklüğünde bir deprem meydana gelmiştir. Bu deprem İzmir şehir merkezinde ve bazı ilçelerinde can ve mal kayıplarına yol açmıştır. Deprem sonrası İzmir ve güneyinde yapılan çalışmalar, en büyüğü Seferihisar'da olmak üzere İzmir ve güneyinde 4-14 cm arasında değişen miktarlarda yatay atım meydana geldiğini göstermiştir. İzmir ve güneyinde ise Mw:6.1 ile Mw:6.9 arasında deprem üretme potansiyeline sahip olan diri faylar yer almaktadır. Meydana gelen bir depremin civardaki fayların neden olabileceği depremleri etkileyebilmesi nedeniyle bu bölgede postsismik deformasyonun takip edilmesi amacıyla 27 noktalık bir GNSS ağı kurulmuştur. Bu ağda 2020-2022 arasında 6 aylık periyotlar halinde 4 kampanya GNSS ölçümü gerçekleştirilmiştir. GNSS verileri kullanılarak tüm noktaların Avrasya sabit hızları elde edilmiştir. Elde edilen sonuçlar ağdaki noktaların hem deprem sonrasında kendi aralarındaki hem de deprem öncesi hızlarla aralarındaki farkların 6 mm'ye ulaştığını, buna bağlı olarak bölgede postsismik etkinin devam ettiğini göstermektedir.

30 Ekim 2020 tarihinde Sisam adası kuzeyinde Mw:6.9 büyüklüğünde bir deprem meydana gelmiştir. Bu deprem İzmir şehir merkezinde ve bazı ilçelerinde can ve mal kayıplarına yol açmıştır. Deprem sonrası İzmir ve güneyinde yapılan çalışmalar, en büyüğü Seferihisar'da olmak üzere İzmir ve güneyinde 4-14 cm arasında değişen miktarlarda yatay atım meydana geldiğini göstermiştir. İzmir ve güneyinde ise Mw:6.1 ile Mw:6.9 arasında deprem üretme potansiyeline sahip olan diri faylar yer almaktadır. Meydana gelen bir depremin civardaki fayların neden olabileceği depremleri etkileyebilmesi nedeniyle bu bölgede postsismik deformasyonun takip edilmesi amacıyla 27 noktalık bir GNSS ağı kurulmuştur. Bu ağda 2020-2022 arasında 6 aylık periyotlar halinde 4 kampanya GNSS ölçümü gerçekleştirilmiştir. GNSS verileri kullanılarak tüm noktaların Avrasya sabit hızları elde edilmiştir. Elde edilen sonuçlar ağdaki noktaların hem deprem sonrasında kendi aralarındaki hem de deprem öncesi hızlarla aralarındaki farkların 6 mm'ye ulaştığını, buna bağlı olarak bölgede postsismik etkinin devam ettiğini göstermektedir.

This study presents the capability of the single-frequency (SF) variometric approach (VA) technique with low-cost GNSS observations to detect short-term dynamic behaviors. Harmonic oscillations with amplitudes between 5 and 20 mm and frequencies between 0.3 and 5.0 Hz were generated employing a single-axis shake table to investigate the performance of the SF-VA technique in the structural health monitoring (SHM) system. Besides, a Mw 6.9 Kobe, 1995 earthquake simulation was generated using the shake table to analyze the SF-VA performance for the earthquake early warning (EEW) system. A low-cost u-blox ZED-F9P GNSS receiver and ANN-MB-00 patch antenna were used to collect GNSS observations at a 20 Hz sampling rate during the experiments. The observations were processed using the MATLAB-based open-source PPPH-VA software in real-time (RT) mode, considering eight different satellite combinations. The capability of the SF-VA technique to detect horizontal dynamic behaviors in RT mode was investigated in the frequency and time domains, accepting the displacements from the linear variable differential transformer sensor as a reference. The results in the frequency domain demonstrate that the SF-VA technique with low-cost GNSS observations can successfully detect the peak frequency value of short-term harmonic oscillations up to 5 Hz. Moreover, time domain findings emphasize that the short-time dynamic oscillations can be determined with the SF-VA technique with an accuracy ranging from 0.8 to 6.4 mm. Earthquake simulation experiment results demonstrate that the strong ground motions caused by mega earthquakes can be determined at mm-level by the SF-VA method. The results of both experiments show that multi-GNSS observations contribute to the SF-VA technique considerably. Overall, the findings reveal that the SHM and EEW systems can be operated with low-cost GNSS receivers, and the natural frequency of the man-made structures and accurate displacement values of seismic waveforms can be determined in RT with the SF-VA technique.