Alpay Özdemir

Recent studies have shown that large earthquakes can induce deformation at distances significantly greater than those predicted by simple elastic half-space models. This observation indicates that regional-scale effects must be considered when assessing post-earthquake deformation and seismic hazard. Several studies have demonstrated that the 6 February 2023 Kahramanmaraş earthquake doublet (Mw 7.8 and Mw 7.6) affected distant regions in addition to the immediately ruptured faults.Within the scope of our project, supported by TÜBİTAK 1001 (Project No. 123Y350), we investigate the current fault activity and seismic hazard of fault segments located north of the 2020 Mw 6.8 Sivrice earthquake and the 2023 Mw 7.8–7.6 Kahramanmaraş earthquakes. Our approach integrates multidisciplinary datasets, including seismology, geodesy (GNSS, InSAR, and creepmeters), and geology (morphometric analyses). The study area comprises the East Anatolian Fault (EAF)–Palu segment, the North Anatolian Fault (NAF)–Yedisu segment, and the Karlıova Triple Junction (KTJ).Following the 2020 Mw 6.8 Sivrice earthquake, seismicity increased along several sections of the EAF. Initially, aftershocks were concentrated within the rupture zone and subsequently migrated southwestward, while no significant increase in seismicity was observed along the Palu segment to the north. Approximately three years later, the Kahramanmaraş earthquake sequence (Mw 7.8 and Mw 7.6) occurred on 6 February 2023, after which seismic activity expanded over a broad region along the EAF. Compared to the ruptured areas and their immediate surroundings, seismicity remained relatively sparse along the northern sections of the EAF, where our study area is located.The Palu segment lies adjacent to the NE the Sivrice earthquake rupture zone and forms part of the EAF, whereas the Yedisu segment, located on the NAF, is characterized by a long-term slip deficit and is considered a seismic gap. The Karlıova Triple Junction represents the intersection of the North and East Anatolian faults and exhibits a complex faulting system resulting from active continental collision. Each of these fault segments displays distinct kinematic characteristics and has been affected by the 2020 and 2023 earthquakes to varying degrees.The current seismicity distribution within the study area (Palu, Yedisu, and KTJ) indicates that earthquake clusters observed prior to these large events remain active, with no anomalous seismic behavior identified to date. Despite the relatively low level of seismicity along the Palu segment compared to the main rupture zones, geodetic observations suggest that its well-known creep velocity has accelerated following the 2020 and 2023 earthquakes. In addition, we investigate the relationship between long-term and present-day geodetic deformation rates, morphological indicators, and slip deficits along active fault branches using continuous and campaign GNSS measurements together with InSAR data. These multidisciplinary datasets, currently under preparation, will be integrated intofault interaction modeling and seismic hazard assessments for the region at the conclusion of the project.

As a result of the interaction between the Anatolian Plate and the African Plate to the south, and the Aegean microplate to the west, a complex extensional regime has developed across Western Anatolia. This dynamic tectonic framework causes significant crustal deformation and temporal strain accumulation, particularly along the active Fethiye–Burdur and Gökova fault zones. The Aegean region is considered one of the most seismically active areas worldwide. The Mw 6.7 earthquake that occurred within the Gulf of Gökova on 21 July 2017 represents one of the most recent destructive earthquakes in the region. Despite the pronounced seismic activity in this area, no active fault zones are mapped in this section of the Turkish Active Fault Map. The absence of mapped active structures has highlighted the necessity of detailed investigations into the region’s present-day tectonic deformation characteristics. Within the scope of this study, the aim is to determine crustal deformation and temporal strain accumulation based on Global Navigation Satellite System (GNSS) observations. For this purpose, the region has been monitored since 2021 through campaign-based GNSS measurements and data obtained from continuously operating GNSS stations.In the study, GNSS data has been collected from 6 CORS-TR (Turkey National Permanent GNSS Network- Active) stations, 7 Turkey National Fundamental GNSS Network (TNFGN) sites, and 16 campaign GNSS sites. Four GNSS campaign measurements were carried out between 2021 and 2024 .The GNSS data were processed to generate coordinate time series and estimate station velocities using with Bernese GNSS Software version 5.4. Based on these results, a statistically significant velocity field was identified across the region, with horizontal southwest-directed velocities ranging from a maximum of 41.67 ± 1.76 mm/yr to a minimum of 22.05 ± 2.95 mm/yr. Also, temporal strain accumulation in the region was computed using a finite element method . The results indicate that the eastern and western parts of the region are characterized by different strain fields, and that the amount of strain has increased and expanded spatially over the observations.This work is supported by TUBITAK CAYDAG Project Number 121Y3

Active faults release part of the elastic strain energy stored in the crust via aseismic slip, either through slow slip events (SSEs) or steady slowly creep. However, spatial and temporal interactions between these different styles of aseismic slip have yet to be quantified especially at depth. Along the central section of the North Anatolian Fault, we apply a Multichannel Singular Spectrum Analysis (MSSA) on GNSS time series of ground motion to detect a 4.8 0.08 shallow SSE (2–5 km depth) lasting for 26 5 days, in agreement with local creepmeter observations. Our observations confirm the recurrence of SSEs next to a steadily creeping section of the fault. Finally, we discuss how steady creep and SSEs interact spatially and temporally along the fault segment.

Elastic dislocation models have been successfully used to model co-seismic displacements in numerous studies. Expected far-field displacements (>500 km) are low and most of the time beyond uncertainty level of the global navigation satellite system (GNSS) measurements. In the case of the moment magnitude 7.8 and 7.6 Kahramanmaraş earthquakes on 6 February 2023, the Türkiye’s extensive and continuous GNSS network allowed us to show that large earthquakes can induce far-field crustal deformations (>700 kilometers), exceeding current predictions from elastic dislocation models. This and the asymmetry of the co-seismic displacements with respect to the East Anatolian fault provides crucial insights about the deformation of Earth’s crust at various scales and the interactions among tectonic plates. It also carries profound implications for seismic hazard assessments and necessitates a new perspective on crustal deformation and earthquake mechanics.

The Pütürge segment of the East Anatolian Fault (EAF) represents a critical link in the tectonic framework of the region. The northeastern end of this segment ruptured during the 2020 Sivrice earthquake (Mw 6.8), while the southwestern end marked the termination of the 2023 Kahramanmaraş earthquakes (Mw 7.7, Mw 7.6). Between these two events, the segment remained a notable seismic gap until the Mw 6.0 earthquake on October 16, 2024.This study utilizes GNSS and InSAR data to examine the deformation dynamics of the Pütürge segment before and after the 2024 earthquake. While the extent of rupture during the October event remains unclear, preliminary geodetic analyses provide valuable insights into strain accumulation, potential creep activity, and coseismic deformation patterns.Our findings contribute to understanding the seismic behavior of the Pütürge segment, emphasizing its importance in seismic hazard assessments and the broader tectonic setting of the East Anatolian Fault.

The increasing availability and affordability of low-cost Global Navigation Satellite System (GNSS) systems have made them a viable alternative for various geospatial applications. However, their performance and positioning accuracy require rigorous evaluation, especially when compared to geodetic-grade GNSS systems. This study investigates the accuracy of low-cost GNSS systems in positioning by comparing their results with those obtained from high-precision geodetic GNSS systems.To evaluate the performance of low-cost GNSS systems, campaign type GNSS measurements were conducted at four points using both low-cost and geodetic GNSS systems. The collected data were processed using the Canadian Spatial Reference System Precise Point Positioning (CSRS-PPP) and the AUSPOS relative positioning services. The positioning results from these services were analyzed to assess the performance of low-cost GNSS systems relative to their geodetic counterparts. Preliminary findings indicate that low-cost GNSS systems exhibit promising accuracy levels in comparison to geodetic systems. The results highlight the potential and limitations of low-cost GNSS technology for scientific and practical applications.This study contributes to the growing body of knowledge on low-cost GNSS technologies and provides insights into their applicability in fields such as tectonic monitoring and geodetic research. Future work will focus on refining processing techniques to further enhance the reliability of low-cost GNSS systems.

Seismic waves from distant earthquakes are known to trigger earthquakes and slow slip events on active faults. However, the underlying physics of such interaction is poorly understood. Dynamic rearrangement of grains in a granular medium, pore pressure changes within that same gouge or the response of a frictional interface have been proposed to explain such distant triggering. The main issue is the lack of observations at various scales of the same triggered slip event in nature, from seconds to years and from the local meter-scale to a full-scale image of induced slip on the fault.We use data from a dense seismogeodetic network, InSAR imagery and four creepmeters located at Ismetpasa along the North Anatolian Fault to quantify the temporal and spatial evolution of a sequence of transient shallow slow slip events triggered by the passage of the waves from the 2023 Kahramanmaras doublet. Cumulative slip amounts to 1 cm over a few months and accumulates in the form of multiple mm-amplitude slip events lasting from minutes to weeks. Slip nucleated initially during the passage of surface waves from the M7.8 Kahramanmaras and M7.5 Elbistan earthquakes. High-rate (1s) GNSS time series were used to derive complete time series of dynamic aerial strain and stress tensors to compute the dynamic change in Coulomb stress change during the passage of surface waves. Although the timing of dynamic Coulomb stress change is consistent with the initiation of the first slip events, it is difficult to physically quantitatively relate the amplitude of the shaking with the amplitude of the slip events. Three of the creepmeters subsequently recorded multiple creep events with logarithmically decaying fault slip (Tau> 1.7 hours) following an initial offset of a few tens of microns. We note that the amplitude of the second slip event, triggered by the M7.5 Elbistan earthquake, is larger than that of the first one, triggered by the M7.8 Kahramanmaras earthquake. Subsequent events in the following weeks initiate when local atmospheric pressure drops severely, a feature that was not observed prior to the sequence. Finally, we observe that, for all these slow slip events, slip rate is slowed down by the local increase in atmospheric pressure with a logarithmic relationship between slip rate and pressure.We interpret these slow slip events as the signature of the progressive weakening of the fault zone, weakening first initiated dynamically by the passage of the surface waves from distant earthquakes and progressively continued with the cumulation of slip along the fault. The first incoming waves from the Kahramanmaras earthquake dynamically re-arrange material in the fault gouge, initiating a slip instability at depth, potentially further facilitated by elevated pore pressure, then progresses to the surface and expands along the fault. Each wave train further weakens the fault plane allowing for more slip, which itself further weakens the fault. Once no strain is available, the fault recovers and regains its strength over time. Our study provides a first view of the dynamics of triggered events by combining seismological, geodetic and atmospheric observations.

The East Anatolian Fault (EAF) is an approximately 420 km long sinistral strike-slip fault extending between Karlıova (Bingöl) in the northeast and Türkoğlu (Kahramanmaraş) in the southwest. The earthquake in Sivrice (Elazığ) on January 24, 2020, with a magnitude of Mw 6.8, along with the earthquakes in Pazarcık (Kahramanmaraş) on February 6, 2023, with a magnitude of Mw 7.8, and Elbistan (Kahramanmaraş) with a magnitude of Mw 7.6, has increased the seismic potential of the left-lateral strike-slip East Anatolian Fault.This study involved a total of 12 campaign measurements conducted at a GNSS network consisting of six sites in Palu (Elâzığ) segment of EAF between the years 2015 and 2023. The distance of the survey GNSS sites and continuous GNSS stations from the fault varies between approximately tens of meters to hundred of kilometers. Before and after the earthquakes on February 6, 2023, near field GNSS data were utilized in the analysis of crustal movements related with the earthquakes in 2020-2023. The estimated deformation in the GNSS network campaign results between September 2021 and September 2023, varies from approximately 10 ± 2.6 mm to 40 ± 2.9 mm in Palu segment. These estimations include not only the postseismic effects of the 2020 Sivrice (Elaz) earthquake, but also the coseismic and early postseismic effects of the 2023 Kahramanmaraş earthquake sequence, along with ongoing shallow creep observations.

On January 24, 2020 the Mw 6.8 Sivrice (Elazığ) earthquake was arrested by the ~80 km long Pütürge segment. On February 6, 2023, the first earthquake of the Kahramanmaras Earthquake Sequence, also ended at the southwest end of this segment. Is it creep also that arrest 2023 Pazarcik rupture? We analyzed InSAR data over the Pütürge segment to answer this question. We used over 5000 ARIA standard product interferograms from two ascending and two descending tracks of the Sentinel-1 satellites and the MintPy software to produce InSAR time series and velocity maps for the area. Also we processed both survey and continuous GNSS data with GAMIT/GLOBK GNSS software (v10.7) from 2014. We analysed the results in three time periods – before, between, and after the two earthquakes. InSAR shows that before both earthquakes the segment was creeping and GNSS data is confirming that outcome. We also are searching for any unbroken part of this segment and if this could be another danger in the future.This work is supported by TUBITAK project numbers 114Y250, 118Y435 and 121Y400.

The Aegean region is under the influence of tectonic extension due to subduction zone along the Hellenic Arc. This extension leads to many earthquakes of magnitude 6 and above in the region. The earthquake that occurred on July 21, 2017, in Bodrum Mw 6.7 increased curiosity about the region due to the seismic activities in the Gulf of Gökova and the absence of an active fault in the area according to the active fault map published by the General Directorate of Mineral Research and Exploration (MTA). In the nearby region of the 2017 earthquake, there are the Gökova Fault Zone and the Fethiye-Burdur Fault Zone. Morphological linearity and the seismicity are observed between these two fault zones, and some recent studies indicate the existence of active faults. The aim of this study is to determine whether there are active faults in the Akyaka-Ula region with geodetic measurements. For this purpose we started to observe the area with GNSS campaigns and continuous data since 2021.For this purpose, the data of Turkish National Permanent GNSS Network (CORS-TR) continuous stations, Turkish National Fundamental GNSS sites campaign measurements and survey data of a GNSS network established by our research group were processed together. The GNSS network stations were strategically placed in both near field and far field to the potential fault. GNSS data processed by using Bernese 5.2 software. According to the calculations based on the data from TNPGN-Active and TNFGN stations, the region exhibits an southwestward movement at a rate of approximately 3cm/year.This work is supported by TUBITAK Project Number 121Y3