How to model amplification of strong earthquake motions by local soil and geologic site conditions

A simple equation is proposed to describe the physical nature of the frequency dependent amplification of strong earthquake shaking by local soil and geologic site conditions. For high frequencies, the amplification effects compete with anelastic attenuation. For long periods, along the period axis, the amplification can be described by a low‐pass filter with roll‐off near the period for which the quarter wavelength of wave motion in soil, or in sediments, coincides with their thickness. In the intermediate period range the amplification depends only on the impedance jump between the ‘soft’ surface materials and ‘hard’ basement, and is independent of the thickness of soil or of sedimentary layers.