Modification of ground motions for hazard consistent seismic response analysis

Linear scaling and spectrum matching are the two approaches that are widely used in practice for developing ground motions of appropriate intensity for dynamic analysis.. This paper presents an application in a region with a more complex source system, the tri-source hazard Cascadia region of South-western British Columbia. Here the hazard is determined by crustal, sub-crustal and subduction earthquakes, each of which dominates a different period range of the design spectrum. There are no formal guidelines governing this case. Finally, the paper presents a new method, the Variable Target Spectrum, developed at Stanford University, that involves both linear scaling and spectral matching. It is particularly effective in tuning ground motions to hard rock spectra due to the few hard rock motions available and so it is very difficult to get a good fit by linear scaling and consequently the demands on subsequent spectral matching are severe.