Session 1A – Ground Motions and Intensity Measures

1. Session 1A – Ground Motions and Intensity Measures Paul Somerville Andrew Whittaker Greg Deierlein

2. Spectral Values and beyond .. • NGA effort (response spectral prediction) • things beyond spectra … ground motions • next phase of PEER LL-NGA ?? (not yet fully scoped out) • Scaling of Records (do we agree on the approaches being used) • Procedures in building codes have little scientific basis • Spectral matching (not appropriate for nonlinear evaluation?) • DOE (deagg. to separate spectra) • PEER spectral scaling at T1 (or average of several spectral values, or vector intensity measures, e.g., Cornell-Somerville project)

3. Record Scaling (cont.’d) • Dependency of structural characteristics (strength, period, ductility demand) on the scaling question • Scaling violates the earthquake physics. How does the earth science physics (fault rupture, …) dictate the frequency content/magnitude of records as reflected in hazard curve (and epsilons from the median). Bias induced by scaling to spectral values (resulting in overscaling?; use of “epsilon” to condition scaling) • Frequency scaling? • “A nice interactive problem!”

4. Other topics • Transferability – “west coast” hazard thinking to “eastern” earthquakes (smaller events, less frequent large events, different source characteristics, site conditions, etc.) “north-west” (subduction zone) versus “south-west” hazard • PEER NGA project may shed some light on site effects. • Intensity Measures (ground motion and structure dependent) • Basin and edge effects (extreme effects, reflected in attenuation models and hazard maps, interaction with SSI issues) • Extrapolation of motions to large magnitude events (Are we doing this correctly? Too conservative? Can SCEC develop suites of ground motions for use in research and design practice?).

5. Synthetic Motions • Does SCEC or PEER-LL(NGA) have plans to make the various synthetic ground motions available (1D, 3D)? How might the SCEC ITR group contribute. How does this relate the PEER-LL/CDMG project on ground motion selection. • Validation and verification on synthetic and hybrid records. How is this being covered in the PEER-LL and SCEC research. Upon what basis does one validate the methods/records? Focus of SCEC in next two years?

6. NEES, Verticals, Design Practice • NEES – Data repository issues (links between experimental databases and ground motion libraries). SCEC proposal to generate times histories for NEES research. Links with grand challenge proposals. • Vertical components of ground motions can be very important for long-span bridges and NS components in buildings. • Guidance for design communities on ground motion issues (scaling, basin, SSI, …). FEMA is receptive to partnering with SCEC and other organizations. See FEMA 349 (445) PBD action plan.

7. Geographically Dist. Systems • Geographically distributed scenarios versus specific site scenarios (correlations of motions at different sites). • Spatial variation of motions for long structures (SCEC is working on it, but is there active collaboration with engineers).

8. IT issues • Storage of data from strong motion sites, motions and site/bore hole data (Geotechnical Virtual Data Center) • SCEC simulation capabilities should be made more public (design community, emergency response, …). • IT can simplify the IM question by allowing one to access structure-specific hazard models (e.g., on-line nonlinear spectral values).