David Teague, PhD, GE, presented at the 8th International Conference on Earthquake Geotechnical Engineering in Osaka. David had the opportunity to present on “Application of Non-Ergodic Site Response for High Velocity-Contrast Sites in the San Francisco Bay Area”. His presentation compared the findings of traditional (ergodic) seismic-hazard analysis (SHA) to more refined, non-ergodic SHA at two sites in the San Francisco Bay Area. These sites are the Google Landings Campus in Mountain View and the Atlas Block in San Francisco. While the two sites are quite different, they are both characterized by an abrupt change in stiffness at the soil-bedrock interface.
The two case histories illustrate that ergodic SHA methods do not work well on these sites. This is an important finding because many sites in the Bay Area and other regions are characterized by abrupt changes in stiffness at the interface of various strata. On the other hand, non-ergodic SHA methods are well-suited to account for the presence of these stiffness contrasts. Relative to the ergodic SHA results, the non-ergodic results generally showed lower seismic demands over broad period ranges and increases at the fundamental period of the site.
