Teleseismic source inversions of the 2000 sultandağ (Mw≈6.0) and 2002 çay-eber (Mw≈6.4) earthquakes (western Türkiye)

Teleseismic source inversion methods have been employed as a crucial tool for investigating the rupture processes of the 2000 Sultandağ and 2002 Çay-Eber earthquakes. This study focuses on teleseismic data-based source inversion analyses to understand the seismic structure of Western Turkey and to resolve tectonic movements in the region. Teleseismic source inversion is a widely used method for understanding the mechanisms of large earthquakes worldwide, providing effective results in determining the characteristics of earthquake sources. In this context, the study highlights the significance of teleseismic analyses by conducting an extensive literature review of seismic activity in Western Turkey and previous studies in the area. The developed method was applied for the point-source inversion. A summary of the findings is as follows: 2000 Sultandağ Earthquake: The 2000 Sultandağ earthquake was successfully modeled using a single point-source model, which provided a clear explanation of the rupture process. The point source, representing the location of the earthquake's initial rupture, was determined to be situated 6 km southeast of the earthquake's hypocenter at a depth of 9 km. The main rupture event, which is characterized as the primary phase of fault movement, lasted approximately 10 seconds. The corresponding seismic moment, a key parameter that quantifies the energy released by the earthquake, was calculated as 1.11 x 10^25 dyne.cm. This value of seismic moment is indicative of a moderate-to-large magnitude earthquake, with an estimated magnitude of approximately Mw=6.0. Additionally, the geometrical characteristics of the faulting, including the strike, dip, and rake angles, were derived as 294°, 38°, and -82°, respectively. These angles describe the orientation and direction of the fault rupture, with the strike angle indicating the horizontal orientation of the fault, the dip angle representing the angle at which the fault plane dips into the Earth, and the rake angle specifying the direction of slip along the fault. The calculated values suggest a normal faulting mechanism, typical for the region's tectonic setting. 2002 Çay-Eber Earthquake: The 2002 Çay-Eber earthquake was initially analyzed using a single point-source model. However, this approach was later found to be insufficient to fully capture the complexity of the rupture process, and a two-point-source model provided a more accurate representation of the event. The first point source was located 24 km northwest of the earthquake's hypocenter, at a depth of 4 km. The main rupture associated with this point source lasted approximately 15 seconds, with a corresponding seismic moment of 2.93 x 10^25 dyne.cm. This value suggests a magnitude of Mw≈6.3, which is slightly larger than the 2000 Sultandağ earthquake. The strike, dip, and rake angles for this primary point source were calculated as 282°, 54°, and -70°, respectively. These values indicate a fault orientation that is different from that of the Sultandağ earthquake, with a steeper dip and a different direction of slip along the fault. The second point source, which contributed to the overall rupture process, was located 8 km northwest of the hypocenter and at a deeper depth of 16 km. This secondary rupture lasted approximately 8 seconds and had a smaller seismic moment of 0.52 x 10^25 dyne.cm. The strike, dip, and rake angles for this point source were calculated as 261°, 57°, and 50°, respectively. These values indicate that the second rupture was associated with a different fault segment, with distinct fault geometry and a reverse slip mechanism, as evidenced by the positive rake angle. When the two point sources were combined, the overall faulting mechanism of the earthquake was modeled as a composite of both sources, with the resulting strike, dip, and rake angles calculated as 282°, 53°, and -60°, respectively. This two-point-source model provided a more comprehensive understanding of the rupture process, highlighting the complex interaction between different fault segments and rupture modes. The two-point-source model also suggests that the earthquake involved both normal and reverse faulting components, which is consistent with the tectonic environment of the region, where active faulting is influenced by a combination of extensional and compressional forces. Fault Characteristics of the Earthquakes: The solution for the 2000 Sultandağ earthquake indicates that the Sultandağ Fault dips to the northeast and represents a normal faulting rupture moving toward Akşehir Lake. In the case of the 2002 Çay-Eber earthquake, the larger point source indicates a rupture occurring west of Çay district along the east-west segment of the Sultandağ Fault, while the smaller point source shows a relatively smaller-scale rupture between Çay and Sultandağ districts. The methodology section of the study explains how teleseismic analyses are performed and provides detailed information on the data collection techniques, seismic network configurations, and the advanced inversion techniques applied. The data collection process focuses on the collection of broadband P-wave data recorded at teleseismic distances and the advanced seismic network systems used to properly analyze these data. The accurate acquisition of these data is critical for determining the location, depth, and seismic moment of the earthquake source. Additionally, the details of the inversion techniques used, such as the point-source model demonstrate how these methods are applied in such analyses and the accuracy of the solutions they provide. The analyses reveal significant differences in the rupture processes of the 2000 Sultandağ and 2002 Çay-Eber earthquakes. The ruptures are characterized by different source mechanisms, with varying strike, dip, and slip angles. The study emphasizes that the two earthquakes exhibit distinct features, as each occurred on different fault segments and involved different rupture mechanisms. These differences provide a better understanding of the tectonic structures and stress distributions in the region. A comparison of the results offers in-depth insights into the seismotectonic structure of Western Turkey, helping to model the distribution of tectonic stress and rupture processes more clearly. This study not only contributes to a deeper understanding of these specific earthquakes but also provides important implications for seismic hazard assessment and the development of risk mitigation strategies in Western Turkey. Accurate determination of earthquake source characteristics facilitates the creation of more reliable seismic hazard maps for future large earthquakes, which is of great significance given the population density and infrastructure in the region. Furthermore, the data obtained can be used in the development of seismic risk management strategies, particularly in assessing whether settlements and critical infrastructure are at risk. The study underscores the critical role of teleseismic source analyses in understanding earthquake dynamics. Determining the characteristics of earthquake sources is a fundamental tool for understanding how fault systems behave and what types of rupture mechanisms are at play. When combined with local seismic network data, teleseismic analyses provide more comprehensive and accurate results. In this sense, this study not only provides insights into the two specific earthquakes but also serves as a guide for broader future research in seismology. Future studies can continue examining other significant earthquakes and potential hazards in the region, further enhancing the applicability of such analyses on both local and global scales.