PROPOSITION OF A SPECTRAL AMPLIFICATION MODEL FOR NEAR FAULT DIRECTIVITY EFFECT WITH UTILIZING PROBABILISTIC EARTHQUAKE SCENARIOS

Yıl 2018, Cilt: 6 Sayı: ozel, 18 - 27, 01.12.2018

Saed Moghimi Sinan Akkar

Öz

Near fault ground motions with directivity effect show larger spectral demands due to their specific waveform features. Directivity effect occur due to S-wave polarization when the fault rupture propagation and waveform travel direction coincide on each other. In this situation, a pulse arises in the beginning of ground motion displacement and velocity waveforms which is mostly seen in the fault normal direction. The pulse period (Tp) is directly proportional to the earthquake magnitude (moment magnitude, Mw) and its amplitude is inversely proportional to the rupture distance (Rrup) from the site. The other characteristic of the near fault ground motions due to S-wave polarization is known as “Fling Step” in which a residual displacement is seen in the fault parallel displacement waveform. This study summarizes the observations from the effect of near fault ground motions on design spectrum. The results of these observations are used to develop simplified equations for incorporation of near fault effect in design spectrum. Probabilistic seismic hazard scenarios are utilized in this study in order to investigate the effect of fault seismicity, fault length (characteristic magnitude of the fault), pulse period and source-to-site geometry on the level of spectral amplification due to directivity effect. The near fault effect is modelled with assembling two narrow-band directivity models (Shahi and Baker 2011; Chiou and Spudich 2013) on the probabilistic seismic hazard scenarios respectively. In the last part of this study the significance of seismological and geometrical parameters on the level of spectral amplification due to directivity will be shown and discussed. The results are used to propose relationships for the incorporation of near fault directivity effect for different geometrical distributions of the sites around the fault.

Anahtar Kelimeler

Directionality effect, Near fault ground motions, Earthquake hazard, Earthquake Design Codes

Kaynakça

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