Document Type : Original Article
Authors
1
PhD Candidate, Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, Tehran, Iran
2
Assistant Professor, Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, Tehran, Iran.
3
Associate Professor, Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, Tehran, Iran
10.22065/jsce.2024.400292.3135
Abstract
In this paper, alterations of vertical acceleration of the near-field earthquakes have been studied using 41 strong ground motions from 20 earthquakes with 3.9 ≤ M ≤ 7.3, which have been extracted from KiK-net seismograph network (In Japan country). In this respect, the study of the vertical has been conducted in two cases. In the first case, by considering several strong earthquakes, the effect of the vertical acceleration of the near-field earthquakes was investigated to have an insight about the location effects. In the second case, the stations and earthquakes were considered constant and subsequently, the effect of the soil was evaluated.
Accordingly, the transfer functions for the acceleration and velocity frequency amplification factors as well as spectral amplification factors were extracted for the velocity and acceleration spectra. In order to calculate the transfer functions, the ratio of the frequency contents of Time History recorded at the surface and depth was used, and for the spectral amplification coefficients, the ratio of the response spectrum of the surface to the depth with 5% attenuation was used. The most important finding is that soil layers amplify the seismic waves and vertical acceleration. Soil performance depends on factors such as source and direction of release. On the other hand, the presence of one or two layers of soil with completely limited thicknesses on the surface causes a completely different behavior of the construction. In general, the functions of frequency amplification and spectral amplification are similar in a wide range of frequencies. The magnitude of the earthquake could not cause drastic changes in the vertical acceleration transfer function. But soil magnification with the transfer function obtained under different input frequencies could have completely different performance. Major amplification of frequencies in the near field is observed in the range of 3 to 18 Hz.
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