Recipe to Define Near-Field Earthquake Motion for Structural Design

After the brief introduction of the strong motion characteristics of the 1995 Hyogoken Nambu earthquake and the history of destructive earthquakes Occurred in Japan as Well as chronological change of earthquake resistant design codes, we summarize what we learned from this earthquake to define near source motions and the earthquake disaster prevention measures proposed by the Japan Society Of Civil Engineers. To respond the question how to define the design earthquake motion taking into account near source effects we develop simple methods to estimate acceleration response and phase spectra at the ground surface in the region near earthquake source. To estimate earthquake motion on the ground surface a formula Of earthquake emotional baserock level was derived in the frequency domain. The amplification effect of the ground was introduced by using multiple reflection theory. We applied the spectral moment method to estimate an acceleration response spectrum. Actual acceleration response spectra are carefully compared with theoretically estimated response spectra at several observation points where the strong earthquake motions were recorded during the 1995 Hyogoken Nambu earthquake. The concept of group delay time is used to model a phase characteristic of earthquake motion. The time delay caused by rupture propagation on fault plane which is assumed to be expressed by a train of impulses. The effect Of transmitting path and amplification effect due to the 238 local soil condition on phase is assumed to be given by minimum phase function. Using the modeled phase spectrum We propose a method to simulate an input earthquake motion compatible with design acceleration response spectra