Sürdürülebilir Kalkınma Amaçları
Yayınlar
- MakaleAçık Erişim2026Modeling Long-Term Postseismic Deformation Following the 2020 Mw 7.0 Samos Earthquake Using Campaign and Continuous GNSS Observations
Solak, Halil Ibrahim; Tiryakioglu, Ibrahim; Gezgin, Cemil; Aladogan, Kayhan; Yalvaç, Sefa; Aktug, Bahadir; Yigit, Cemal Ozer; Dönmez, Ergin; Demirelli, Ertugrul; Eyübagil, Eda Esma
Highlights What are the main findings? What are the implications of the main findings?Highlights What are the main findings? What are the implications of the main findings?Abstract 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.
- MakaleAçık Erişim2025The 2023 Mw 7.8–7.7 Kahramanmaraş earthquakes were loosely slip-predictable
Vavra, Ellis; Fialko, Yuri; Bulut, Fatih; Garagon, Aslı; Yalvaç, Sefa; Yaltırak, Cenk
Understanding the behavior of large earthquakes over multiple seismic cycles is limited by short time spans of observations compared to recurrence intervals. Most of large instrumentally-recorded earthquakes have occurred on faults lacking well-documented histories of past events. The 2023 Mw 7.8–7.7 Kahramanmaraş earthquake doublet is exceptional as it ruptured multiple segments of the East Anatolian Fault (EAF) system, where historical records of devastating earthquakes span over two millennia. Here, we use historical earthquake records, measurements of interseismic deformation, and published slip models of the 2023 events to evaluate the recurrence patterns of large earthquakes. We compare slip deficit that accrued on each fault segment since the respective penultimate events to the average coseismic slip of the 2023 doublet. We find that the coseismic slip equaled to or exceeded the accumulated slip deficit, suggesting that the slip-predictable recurrence model applies as a lower bound on strain release during the Kahramanmaraş earthquakes.
- MakaleAçık Erişim2024Monitoring Surface Deformations in a Fossil Landslide Zone and Identifying Potential Failure Mechanisms: A Case Study of Gümüşhane State Hospital
Alemdag, Selçuk; Yalvaç, Sefa; Bjelotomić Oršulić, Olga; Kara, Osman; Zeybek, Halil İbrahim; Bostanci, Hasan Tahsin; Markovinović, Danko
The escalating occurrence of landslides has drawn increasing attention from the scientific community, primarily driven by a combination of natural phenomena such as unpredictable seismic events, intensified precipitation, and rapid snowmelt attributable to climate fluctuations, compounded by inadequacies in engineering practices during site selection. Within the scope of this investigation, contemporary geodetic techniques using the GNSS were employed to monitor structural and surface deformations in and around a hospital edifice situated within an ancient fossil landslide region. Additionally, inclinometer measurements facilitated the determination of slip circle parameters. A subsequent analysis integrated these datasets to scrutinize both the hospital structure and its surrounding slopes. In addition to the finite element method, four different limit equilibrium methods (Bishop, GLE–Morgenstern–Price, Spencer, and Janbu) were used in the evaluation of stability. Since the safety number determined in all analyses was <1, it was determined that the slope containing the hospital building was unstable. The movement has occurred again due to the additional load created by the hospital building built on the currently stable slope, the effect of surface and groundwater, and the improperly designed road route. As a result of geodetic monitoring, it was determined that the sliding speed on the surface was in the N-E direction and was approximately 3 cm, and this situation almost coincided with inclinometer measurements.
- MakaleYalnız künye2023Excessive groundwater withdrawal and resultant land subsidence in the Küçük Menderes River Basin, Turkey as estimated from InSAR-SBAS and GNSS measurements
Yalvaç, Sefa; Alemdağ, Selçuk; Zeybek, Halil İbrahim; Yalvaç, Murat
Küçük Menderes River Basin (KMRB) is located in the western part of Turkey in the city of İzmir. The basin hosts about half a million people and 90% of the population makes their living from farming and animal husbandry. Most of the water needs for agricultural irrigation, animal husbandry, and drinking are met from groundwater resources in the basin. Since the water pumped from the aquifers cannot be naturally recharged by surface waters and precipitation, the groundwater level is rapidly receding and a decrease of up to 150 meters has been observed in the historical groundwater level time series since the 1990s. For this reason, land subsidence occurred in the basin and as a result of this, crustal surface cracks have formed and infrastructure and superstructure facilities have been endangered. To prevent loss of life and property that may occur in the future, it has become necessary to estimate the magnitude and the expansion zone of the land subsidence by carrying out geodetic monitoring studies in the region. In this study, the analyzes performed by Interferometric Synthetic Aperture Radar-Small Baseline Subset (InSAR-SBAS) and Global Navigation Satellite System (GNSS) methods to monitor land subsidence in the KMRB are presented. For this purpose, monthly 74 SAR images from 2017 to the end of 2022 were evaluated according to the SBAS procedure in the GMTSAR academic analysis software. In order to, both validate the InSAR-SBAS results and convert the deformation rate in the Line of Sight (LOS) to the ellipsoid normal direction, 3 periods of GNSS campaign were performed between 2021 and 2023 in 5 different GNSS stations and evaluated with the GAMIT/GLOBK software. According to the analyses, the land subsidence rate of up to −165 mm/year has been estimated in the KMRB, especially in the district centers of Bayındır and Ödemiş. In addition, unlike many studies, different rates and propagation of subsidence were determined in different parts of the basin depending on the aquifer type and precipitation. Monthly time series of the deformations were created and the behavior of the deformations and its relationship with the groundwater withdrawal and the lithological structure in the region was scrutinized. Thus, the spatio-temporal behaviour of the land subsidence and the associated geological factors were revealed.
- MakaleAçık Erişim2021Anatomy of october 30, 2020, samos (Sisam) –kuşadası earthquake (mw 6.92) and its influence on aegean earthquake hazard
Bulut, Fatih; Doğru, Aslı; Yaltirak, Cenk; Yalvaç, Sefa; Elge, Murat
We investigated rupture geometry, size, and slip distribution of October 30, 2020, Samos (Sisam)–Kuşadası earthquake combining seismographs, GPS measurements, and SAR analysis. Right after the earthquake, we measured 13 additional campaign-based GPS sites to intensify the available GPS network consisting of 10 continuous stations. We combined all available seismographs to have the best possible accuracy for mainshock and aftershock hypocenter locations. We compiled all available seismic profiles and integrated them using high-resolution bathymetry to map seismically active faults. The mainshock hypocenter is located at 37.913 ± 0.009 N° and 26.768 ± 0.017 E° and a depth of 12.3 ± 1.7 km. Our fault plane solution shows that the mainshock has almost a pure normal-type mechanism. Based on accurate aftershock locations as well as InSAR results, the mainshock rupture is subsegmented with two north-dipping rupture planes. The rupture probably starts on a low angle plane generating 1.1 m average slip between the depths of 9–14 km. It merges to a steep plane at 9 km depth where it generates 1.2 m average slip extending towards the surface near the shoreline of Samos (Sisam) Island. Total size of the two rupture planes and their average slips determine that the magnitude of the mainshock is (Mw ) 6.92 ± 0.02. The mainshock has substantially increased Coulomb stress on several fault segments near the towns Kuşadası and Söke, which have the potentials to generate strong earthquakes. It also nonnegligibly increased Coulomb stress on several fault segments south of İzmir giving a warning for increased earthquake hazard in this highly inhabited area.
- MakaleYalnız künye2018Multipath interference cancelation in GPS time series under changing physical conditions by means of adaptive filtering
Üstün, Aydın; Yalvaç, Sefa
Multipath, a highly autocorrelated signal is observable phenomena during time periods longer than the sidereal period of Global Positioning System (GPS) satellites in their constellations. Multipath pattern and sidereal repeat time interaction are examined in terms of time series correlations of topocentric coordinates using GPS code and phase observations collected at high and low frequencies. The horizontal and vertical components at 5 and 30 s sampling rates are analyzed to detect and remove multipath classified by their MP1 levels and baseline lengths. For the selected 11 stations that have 24-hour data from CORS stations in the USA and Turkey, the repeat times of the GPS constellation were identified as a function of maximum cross-correlation of adjacent time series. The multipath interference signal from two-day time series data is removed by an adaptive filter to improve time series of coordinate estimates. After the filtering process, an effective epoch based position tracking has been accomplished, especially in the height component. The position errors disappeared to maximum possible extent in the pseudo-range measurements. Up to 70% improvement for the phase derived coordinates in reflective environment has been achieved over the baselines ranging from 1 km to 175 km. For the phase observables, the filter success directly related to the multipath level which is specific to the station.