The intensity of ground shaking and the demand on structures during earthquakes have been generally characterized using parameters such as peak ground acceleration as well as strength-based parameters such as response spectrum ordinates (e.g., spectral acceleration) that represent the maximum amplitude of shaking for structures with specified natural period and damping values. It has long been recognized that to assess the demands on structures during earthquakes, one might employ an energy-based approach (as an alternative to the more common strength-based one), especially when there is an interest in assessing damage potential of ground motions. An energy spectrum, obtained with the same level of effort required to construct a conventional response spectrum, is a convenient single-parameter description of both amplitude and duration of ground motion and can serve as a useful means by which to describe the performance of structures with different natural periods and damping ratios.
In this study, attenuation models for Northwestern Turkey are developed for two parameters (defined herein) that are related to input energy and absorbed energy. The empirical models developed take advantage of the recent increase in the database on strong motion data for Northwestern Turkey. A total of 195 recordings from 17 recent seismic events are included in this database. The ground-motion prediction equations developed are for the geometric mean of the two horizontal components of the 5-percent damped energy parameters (elastic and inelastic input energy-equivalent acceleration, Ai, and absorbed energy-equivalent velocity, Aa) at various periods. Predictions of the energy-based parameters from the proposed attenuation model are compared with (strength-based) spectral acceleration levels predicted by Özbey et al [Soil Dyn. & Earthq. Eng., 24 (2004), pp. 115-125]. It is found that the energy demand parameters were generally greater with elastic Ai demands highest. In addition, the predicted energy-based parameter levels are compared with available Western U.S. attenuation model predictions for the same energy-based parameters. Western U.S. models predict similar energy demands to those with the proposed model.
Finally, amplification factors for the energy-based parameters are proposed as a function of site class; these factors can be thought of as analogous to amplification factors for spectral acceleration as given in the NEHRP Seismic Provisions. The patterns related to the amplification are similar as with spectral acceleration in NEHRP (2001). A comparison of soil amplification effects for strength- and energy-based parameters is also discussed.