Characterizing soil dynamic parameters through ambient seismic noise in the Sakarya region of the north anatolian fault system

Abstract This study characterizes the dynamic properties of soils in the seismically active Sakarya Region, located within the complex tectonic structures of the North Anatolian Fault Zone, using ambient seismic noise data collected from 63 stations. Parameters such as Vs 30 , peak ground acceleration (PGA), horizontal-to-vertical spectral ratio (HVSR), directionally dependent HVSRs (NS/UD and EW/UD), seismic vulnerability index ( K g ), and ground shear strain (GSS) were evaluated in a multi-dimensional framework. The distributions of Vs 30 and PGA indicate weak soil conditions and elevated seismic hazard, particularly in areas near fault zones. HVSR analyses identified low-frequency (0.35–2.4 Hz) and high-amplitude (> 6.0) resonance patterns in alluvial zones. Directionally dependent HVSRs revealed pronounced azimuthal amplification differences in areas where directionally dependent coefficients ( γ ) are greater than 0.7, which are closely associated with lateral heterogeneity. K g values (ranging from 0.34 to 285) and GSS assessments highlight zones with potential nonlinear deformation behavior under seismic loading. However, parameters such as Vs 30 and PGA represent regional-scale estimates derived from external datasets and probabilistic hazard models rather than site-specific measurements. Therefore, the spatial patterns identified in this study should be interpreted as indicative trends reflecting relative site conditions. These results emphasize the importance of integrating directional resonance characteristics and deformation-based metrics into seismic hazard assessments, offering a comprehensive approach for identifying critical zones and informing resilient engineering design and land-use planning in tectonically complex regions such as the Sakarya region.