Sreeram Reddy Kotha

Supervisor: Prof. Dr. Fabrice Cotton (GFZ)

Project: Site-specific Probabilistic Seismic Hazard Assessment

Building design codes, catastrophe risk models and disaster mitigation procedures are formalized based on the outcomes of a Probabilistic Seismic Hazard Assessment (PSHA). Hazard, the rate of exceedance of ground-shaking intensity level at a site, is estimated for the regional seismicity with a seismic intensity attenuation model – typically, empirical Ground Motion Prediction Equations (GMPEs). Given the seismic source-path-site parameters, a GMPE predicts the median intensity level (μ), while its residual variance (σ2) reflects the apparent natural randomness of recorded data.

Under the so-called ergodic assumption, σ of GMPEs developed from global strong-motion datasets is inflated by the local diversity of seismic processes. A larger σ implies a higher hazard, which demands conservative (expensive) building design. It is therefore of key scientific and practical interest to reduce σ, and achieve fully non-ergodic ground-motion predictions.

Our mixed-effect residual analyses on pan-European datasets revealed significant regional differences in path- and site-effects between Turkey and Italy – facilitating a ~30% reduced σ in partially non-ergodic GMPEs. Currently, we are complementing mixed-effect regressions with hierarchical cluster analysis on larger strong-motion datasets to further non-ergodicity in PSHA. Our pursuit is aimed at refinement of pan-European seismic hazard maps and revision of European seismic design codes, Eurocode8.