Single-Site Ground Motion Prediction Equations (SS-GMPE) of Response Spectra

地震動予測式

We studied characteristics of strong ground motions from the Off-Sanriku outer-rise earthquakes; these earthquakes are activated after the 2011 Tohoku earthquake (Mw 9.0). First, we calculated pseudo velocity responses for five outer-rise earthquakes (Mw 6.0-7.6) and compared them with the attenuation formulae which were constructed for the intraslab earthquake. In spite of outer-rise's data being over the distance range of these formulae, the extrapolated formulae generally explained the attenuation relations of these observed data. However, there were considerable residuals between the observed and predicted values. These residuals result from the site and source effects, because the previous attenuation formulae were constructed based on many site's strong motion records from many earthquakes occurring at various source areas. Second, in order to overcome the weakness of the previous attenuation equations, we proposed empirical ground motion prediction equations for a single site; we named these equations “Single-Site GMPE (SS-GMPE)”. Our data for regression analysis were strong motion records at a single observation site from the five outer-rise earthquakes occurring at the narrow source area with the radius of about100km. We carried out a regression analysis with respect to Mw for each site assuming the previously estimated internal attenuation for intraslab earthquakes. The earthquake source, propagation path and site effects were well incorporated into these equations, and as a result, the residuals between the observed and predicted values were considerably decreased. Finally, we applied the SS-GMPE to earthquakes not used in the regression analysis and found the good correspondence of predicted and observed spectra.