Geosyntec provides comprehensive seismic hazard services including regional seismic hazard analyses, site-specific seismic hazard adjustments, development of earthquake ground-motion record suites, development of floor design spectra, and seismic risk analyses.

For owners of high-consequence dams, Geosyntec is experienced at implementing experience-based modifications to the seismic source characterization and ground-motion models implemented in these software programs which can result in improved quality and consistency of the seismic hazard assessments. Geosyntec performs Probabilistic Seismic Hazard Analysis (PSHA) calculations using both HAZ45 and OpenQuake.

Dams are commonly sited on hard rock, and thus often require a seismic hazard correction to account for the effects of increased kappa and decreased near-surface shear wave velocity as compared to that considered in regional PSHAs. Geosyntec has extensive expertise and industry relationships pertaining to geophysical investigations and leverages these factors to provide accurate and economical site-specific seismic hazard correction services.

Geosyntec selects ground-motion records which well-represent the seismic source hazard and dam site characteristics and provide pair-rotation, scaling, and spectral matching services to develop suites of ground-motion records. Both uniform hazard spectra and conditional mean spectra conditioned at the significant periods of vibration of dam structures can be used as target spectra, depending on the main structures of interest in the response history analysis and whether floor design spectra will be required for the design of appurtenant structures.

To calculate the seismic response of earthen and concrete dams, our team uses a variety of tools ranging from simplified methods to advanced finite element and finite difference methods that are appropriate to the needs of the project and the client. The results of these analyses are used to develop System Response Probabilities (SRP) as a function of ground motion intensity and reservoir stage for relevant seismic potential failure modes in semi-quantitative and quantitative risk assessments.