Joint inversion of H/V and SPAC methods: A case study of Eskişehir Basin

The analysis of seismological data is crucial for understanding subsurface structures and informing earthquake engineering practices. The Eskişehir Plain, a significant agricultural and industrial hub in Turkey, is experiencing rapid urbanization. To obtain one-dimensional (1D) seismic velocity profiles, the microtremor records collected at seven different points and multi-layered initial model was assumed within the study area were subjected to an inversion process. This approach provided detailed information about the subsurface structure of different regions within the plain. The basin, characterized by a flat plain surrounded by elevated regions, was investigated using Nakamura's H/V spectral ratio and SPAC methods to determine shear wave velocity (Vs), sediment thickness (h), and dominant frequency (f). Inverse modeling with a 7-layer initial model and Monte Carlo simulation was employed to obtain S-wave velocity depth profiles. Results indicate a highly variable subsurface structure. Engineering bedrock depths ranged from 20 to 130 meters, with corresponding Vs values reaching approximately 530 m/s. Dominant frequencies were observed at 0.6 Hz, 0.8 Hz, 1.3 Hz, 3 Hz, and 8 Hz. These variations in subsurface properties suggest that seismic risk is spatially variable within the plain. The findings from this study have significant implications for urban planning, earthquake-resistant design, and disaster risk reduction in the Eskişehir Plain.