The financial cost of repair and interrupted business are significant parts of the earthquake hazard that must be considered.
To assist city planners in mitigation activities, USGS scientists have begun to carefully document the seismic response and characteristics of critical structures in and near Seattle.
Generating a data base of dynamic characteristics of critical structures will:
- allow assessment of the current seismic capacity of the structure
- allow prediction of the structure's expected response in a future large earthquake
- allow comparison of pre- and post-earthquake test data
- allow detection of invisible damages and the reasons for damage in the structure after an earthquake
The field tests involve synchronized recording of structures' vibrations at several locations using portable digital recorders fitted with velocity and acceleration sensors. The excitation sources for the vibrations include impulse hammers, shear-wave generators, earth thumpers, eccentric-mass shakers, and ambient forces. Depending on the funding, one or two structures will be tested every year.
For selected structures that are tested, finite element models that match the test data will be developed, and the expected responses to future large earthquakes in the region will be calculated. The results will be used to assess the seismic safety of these structures, and to provide guidelines for retrofitting.
