Complementary Physical Dimensions of Vrancea (Romania) Intermediate-Depth Ground Motions: Intensity Measures and Their Implications for Sustainable Structural and Geotechnical Risk Assessment

Ground-motion intensity measures (IMs) are key parameters for seismic hazard and risk assessment. However, seismic hazard characterization and code-based design spectra commonly rely on a limited set of parameters, particularly peak ground acceleration (PGA), spectral acceleration, and control periods defining spectral shape. Such representations may not fully capture seismic input relevant to structural response, soil deformation, slope instability, and indirect environmental impacts. This study analyzes 220 horizontal accelerogram components recorded during the Vrancea earthquakes of 4 March 1977, 30 August 1986, 30 May 1990, and 31 May 1990. Twenty-three IMs were computed, covering peak and effective amplitudes, velocity-related measures, cumulative and energy-based indicators, spectral intensities, duration, cyclicity, and impulsivity, together with a set of frequency content-related parameters. Pearson and Spearman correlations were evaluated using both the geometric mean and the maximum of the two horizontal components. Hierarchical clustering, PGA-centered correlation profiles, event-specific comparisons, and spatial representations were used to assess redundancy, complementarity, and relationship stability. Results show that amplitude-, velocity-, and spectrum-related IMs form strongly correlated groups, whereas duration, cyclicity, and impulsivity remain more distinct. Spatial comparisons also show that different IMs may produce different station rankings and regional patterns for the same event. These findings support selecting complementary IM families for more comprehensive, risk-informed structural and geotechnical applications.