Insights into Seismic Site Response in San Fernando and San Gabriel Basin using Geomorphometric Parameters

Ana Sotelo Romero, Rashid Shams, & Chukwuebuka C. Nweke

Submitted September 7, 2025, SCEC Contribution #14740, 2025 SCEC Annual Meeting Poster #TBD

Seismic site response is a critical component of Ground Motion Models (GMMs). Recent studies have shown that sedimentary basins with complex subsurface geometries can significantly amplify ground shaking. However, many current GMMs represent site conditions using one-dimensional features, neglecting multidimensional components of seismic wave propagation effects due to complex subsurface geomorphological and geological variability. This study evaluates whether geospatial parameters can improve the characterization of site response variability in the San Fernando and San Gabriel Basins, two tectonically active basins with complex depositional histories shaped by strike-slip and thrust fault systems. These two settings exhibit substantial heterogeneity in crystalline basement depth and ground topography.

We examined the geologic structure of these basins using geologic cross sections and two Community Velocity Models (CVM-H 15.1 and CVM-S4.26.M01). GIS-based methods were applied to derive geomorphometric indices, including slope, curvature, aspect, and the Topographic Roughness Index (TRI) from high-resolution digital elevation models and basement depth maps. Seismic stations were classified into geomorphic categories (basin interior, basin edge, valley, and mnt/hills) based on topographic setting, enabling the spatial integration of earthquake recordings with geomorphic variables and refinement of basin outlines were refined.

Correlations between geomorphometric attributes and site response were assessed using mixed effects-based site residuals across multiple periods. Slope, TRI, and standard deviation of z1.0 showed the strongest spatial trend with site response, with slope and TRI negatively correlating at longer periods, and standard deviation of z1.0 showing reduced dispersion in residuals. Results indicate that specific geomorphic indicators capture systematic spatial trends in site response, reflecting both surface morphology and underlying basin geometry. This integrated approach advances the development of a non-ergodic site response modelling framework by incorporating both shallow geomorphic features and deep structural controls.

Citation
Sotelo Romero, A., Shams, R., & Nweke, C. C. (2025, 09). Insights into Seismic Site Response in San Fernando and San Gabriel Basin using Geomorphometric Parameters. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology