Characterizing Soil Dynamic Parameters through Ambient Seismic Noise in the Sakarya Region of the North Anatolian Fault System

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), directional HVSR, seismic vulnerability index (Kg), 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. Directional analyses revealed pronounced azimuthal amplification differences in areas where γ > 0.7, which are closely associated with structural discontinuities. Kg values (ranging from 0.34 to 285) and GSS assessments highlight zones with nonlinear deformation potential and elevated seismic risk. These findings underscore the necessity 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.