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[U13-08] Strong ground motion simulation of the 2023 Turkey earthquake using the corrected empirical Green's function method
Keywords:the 2023 Turkey earthquake, Strong ground motion simulation
The 2023 Turkey earthquake occurred on February 6, 2023 with Mw 7.8. The rupture started on a branch of East Anatolian Fault (EAF) in Kahramanmaras province, southeastern Turkey. The rupture moved to the EAF and propagated bilaterally to the northeast and southwest. Surface ruptures with the range of 300 km were detected after the earthquake. Many strong ground motions were recorded along the EAF during the Mw 7.8 earthquake and aftershocks. These records are available from the website of AFAD. There are not many earthquakes with Mw 7.8 and many near-surface strong motion records available. Thus, analyzing the causes of strong ground motions is important for strong ground motion prediction of future large earthquakes.
In this study, strong ground motion simulations of the 2023 Turkey earthquake were conducted. The mechanisms of strong ground motion generation were investigated. The corrected empirical Green’s function method was used in the simulation. We first conducted spectral inversion analysis using aftershock data to evaluate empirical path and site amplification factors. Strong ground motion simulations were conducted using estimated path and site amplification factors. Rectangular asperities were used for the source. Simulations were conducted focusing on capturing the main phases of observed strong ground motions, thus parameters were not optimized. Target sites of the simulations were limited to the southwest side of the epicenter, where strong motions were densely recorded.
Surface ruptures can have strong effect on the near-fault strong ground motions as was observed in the 2016 Kumamoto earthquake. Near-fault strong motions of the 2016 Kumamoto earthquake can be characterized by the fault-parallel step-like displacement and strong velocity pulses. In addition, the directivity effect is another important factor to be considered. Observed strong ground motions of the 2023 Turkey earthquake showed both fault-parallel fault-normal strong velocity pulses, which exceeded 100 cm/s at some stations. Fault-normal pulse periods ranged from 3 s, which may be due to asperities, to 10 s, which may be due to the rupture propagation on the fault as a whole. Fault-normal fling-steps were confirmed by the opposite polarities of fault-normal component on both sides of the fault. Therefore, it is essential to appropriately combine both near-surface ruptures and asperities in the simulation. In this study, as a preliminary simulation, we used only asperities and aimed at capturing the main phases of observed strong ground motions assuming that high-frequency components were mainly generated by asperities. Modeling near-surface ruptures is one of the future tasks.
Empirical path and site amplification factors for the simulation were estimated by spectral inversion of small earthquake records. We used 736 records from 56 sites and 44 earthquakes. All the strong motions used were manually checked. A nonparametric inversion scheme was used. The source spectrum of the earthquake of 18:33, February 12, 2023 (Mw 4.6) was used as the constraint.
Strong ground motion simulations were conducted using the corrected empirical Green’s function method. Synthetic strong ground motions by this method consist of source, path, site amplification and site phase characteristics. Path and site amplification factors estimated by the inversion were used. Seven asperities were used in the simulation. Fault planes along the surface ruptures and the dip angle of 90° were assumed. Although the number of asperities and parameters can change in the future, the result suggests that strong motions were generated by continuous rupture propagation rather than by a small number of asperities. Good agreement was obtained in the acceleration time histories and Fourier spectra. Future tasks include the detailed modeling of strong pulses in fault-parallel and fault-normal components and adding near-surface ruptures.
In this study, strong ground motion simulations of the 2023 Turkey earthquake were conducted. The mechanisms of strong ground motion generation were investigated. The corrected empirical Green’s function method was used in the simulation. We first conducted spectral inversion analysis using aftershock data to evaluate empirical path and site amplification factors. Strong ground motion simulations were conducted using estimated path and site amplification factors. Rectangular asperities were used for the source. Simulations were conducted focusing on capturing the main phases of observed strong ground motions, thus parameters were not optimized. Target sites of the simulations were limited to the southwest side of the epicenter, where strong motions were densely recorded.
Surface ruptures can have strong effect on the near-fault strong ground motions as was observed in the 2016 Kumamoto earthquake. Near-fault strong motions of the 2016 Kumamoto earthquake can be characterized by the fault-parallel step-like displacement and strong velocity pulses. In addition, the directivity effect is another important factor to be considered. Observed strong ground motions of the 2023 Turkey earthquake showed both fault-parallel fault-normal strong velocity pulses, which exceeded 100 cm/s at some stations. Fault-normal pulse periods ranged from 3 s, which may be due to asperities, to 10 s, which may be due to the rupture propagation on the fault as a whole. Fault-normal fling-steps were confirmed by the opposite polarities of fault-normal component on both sides of the fault. Therefore, it is essential to appropriately combine both near-surface ruptures and asperities in the simulation. In this study, as a preliminary simulation, we used only asperities and aimed at capturing the main phases of observed strong ground motions assuming that high-frequency components were mainly generated by asperities. Modeling near-surface ruptures is one of the future tasks.
Empirical path and site amplification factors for the simulation were estimated by spectral inversion of small earthquake records. We used 736 records from 56 sites and 44 earthquakes. All the strong motions used were manually checked. A nonparametric inversion scheme was used. The source spectrum of the earthquake of 18:33, February 12, 2023 (Mw 4.6) was used as the constraint.
Strong ground motion simulations were conducted using the corrected empirical Green’s function method. Synthetic strong ground motions by this method consist of source, path, site amplification and site phase characteristics. Path and site amplification factors estimated by the inversion were used. Seven asperities were used in the simulation. Fault planes along the surface ruptures and the dip angle of 90° were assumed. Although the number of asperities and parameters can change in the future, the result suggests that strong motions were generated by continuous rupture propagation rather than by a small number of asperities. Good agreement was obtained in the acceleration time histories and Fourier spectra. Future tasks include the detailed modeling of strong pulses in fault-parallel and fault-normal components and adding near-surface ruptures.