Correlations of Horizontal and Vertical Spectral Accelerations for the Chilean Subduction Zone

This study develops parametric models for the correlation between vertical and horizontal components of spectral accelerations in the Chilean subduction zone. The models are based on seismic records from national databases and recent ground motion models developed for the region. The effects of magnitude, distance, site conditions, and model selection on correlations are evaluated and found to be negligible, supporting the use of a simplified formulation. The proposed models are compared to existing models developed for other regions, showing significant differences, especially for inslab earthquakes. Despite these differences, the impact on practical applications is limited due to the low sensitivity of hazard estimates to variations in correlation at low correlation values. The results are suitable for use in seismic hazard analyses that incorporate vertical ground motion, enabling more comprehensive assessments for structures sensitive to this component. The study highlights the importance of developing region-specific models and identifies future needs, including expanding local ground motion models to additional intensity measures and refining correlation functions to better capture differences between interface and inslab events.