A Study on Empirical Ground Motion Estimation Introducing Fault Rupture Propagating Effects

Abstract eng:
Fault rupture propagating effects such as radiation pattern and forward directivity, are introduced into empirical attenuation relationship of ground motion. In this study, those effects are theoretically defined using the directions of rupture propagation, fault slip, and wave radiation pattern of small sub-faults divided from target fault as used in the Green’s function summation technique. Rupture heterogeneity is also considered as a weight of seismic moment for each small sub-fault. Empirical relationship between site amplification and average shear wave velocity are introduced to estimate shake map. The modification factors to correct the rupture propagating effects are applicable for any attenuation formulae of maximum acceleration or velocity, because the average of the factors for wide area around the target fault are defined to be constant value as one. Using the factors, different ground motion maps are obtained for strike and dip slip faults even using an attenuation formula with magnitude and fault distance which does not care about fault rupture type. The effects of proposing modification factors are verified by using ground motion distributions derived from observed past earthquakes and wide frequency band waveform simulations. The proposing method provides more realistic ground motion distributions than those by original attenuation formula. The proposing technique can be applicable for quick estimations of ground motion distribution in wide target area as required in immediate action just after the earthquake.

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