A LOGIC TREE EXTENSION OF THE CAPACITY SPECTRUM METHOD DEVELOPED TO ESTIMATE SEISMIC RISK IN OSLO,NORWAY

The city of Oslo, Norway, was affected by a magnitude 5.4 earthquake in 1904 causing widespread minor damage. The earthquake occurred around 100 km south of Oslo within the Permean rift structure that runs North-South along the Oslofjord, and deep clay deposits under the city contributed to the damages. A seismic risk scenario including soil amplification and buildings classifications has been conducted with two earthquake sources, one very close to the city and one near the 1904 epicenter. Both scenarios exhibit strong dependencies on the soft clays underlying large parts of Oslo. The results confirm the 1904 effects, but also show a strong dependency on the applied attenuation functions. All computations are based on the capacity-spectrum method, and the predefined pushover curves and vulnerability functions were adopted from the HAZUS code. With this basis, the computational scheme was developed independent from the GIS framework, and a weighted logic tree formulation was implemented for appropriate treatment of epistemic uncertainties.