Linear and Nonlinear Site Response Evaluation Using Single-Station Time-Frequency Analysis: Applications Across Regions

Understanding site response is important for assessing seismic hazards. We present methods — Time-Frequency Resonance Analysis (TFRA) and the Envelope of the Power Spectrum of Displacement to Jerk (EPSDJ) for analyzing both linear and nonlinear site responses. These techniques require only a single surface station with weak to strong motion records, eliminating the need for a reference site. While they do not provide site amplification values, they effectively identify broadband site resonances and nonlinear site behavior.

The methods are first applied to seismic data from KiK-net, Japan, with borehole responses serving as a benchmark. We then extend the analysis to southeastern Türkiye, comparing results with Horizontal-to-Vertical Spectral Ratio (HVSR) and Generalized Inversion Technique (GIT) methods to identify the most effective combination for site response assessment in the region. After validation in regions with reference data, the method is applied to seismic records from the Taiwanese seismic network across diverse geological settings. 

The results highlight the complexity of site response, with linear and nonlinear behaviors varying across frequency bands and regions. We observe that local geology significantly influences the ground motion, controlling the seismic hazard and its uncertainty over a broadband frequency range. The evaluation includes nonlinear behavior in the regions of interest, identifying stations that are more susceptible to nonlinearity, and quantifying both local and regional levels of nonlinear site response. Additionally, the findings indicate that nonlinearity can manifest during weak motion (< 30 cm/s²), a behavior observed consistently across all regions studied.