Probabilistic seismic hazard assessment by, considering the effects of near-field directivity (A case study of Kermanshah region)

Articles in Press

Document Type : Research Article

Authors

1 Nothing

2 Faculty Member, Iranian strong motion network, Road , Housing & Urban Development Research Center

3 Graduated Student in Seismology, Institute of Geophysics, University of Tehran

Abstract

The near-fault zone movements exhibit long-period pulses in the time history diagram of their velocity and displacement, causing changes in displacements and large velocities. The acceleration reflection spectrum of the earthquakes recorded in the stations located near the fault is out of the usual shape, and in the period of intervals greater than 7 seconds, the amplitudes of the reflection spectrum increase significantly. The orientation of the structure near the fault is crucial, and the directionality effect should be considered due to the high relative risk in the studied area. Near-field records have a different nature compared to far-field records due to having a large pulse in the time history, and the existence of this pulse causes significant damage to the structure. Rupture starts from a point along the fault and propagates in the beginning, end, or both directions. The propagation of rupture along the fault and the effect of rock fracturing velocity on shear wave velocity is called directivity. When the direction of rupture propagation is towards the site, the directivity effect can cause pulses with large amplitudes and medium to long periods. Directivity changes the energy distribution over time and can also occur in moderate and small earthquakes. Therefore, in addition to the distance to the fault, the direction of rupture propagation is also important.

A study on the probabilistic seismic hazard analysis in Kermanshah province showed that increasing the structural period and return period increases the ground motion acceleration. The greatest acceleration increase occurs in the 4-second period and 2475-year return period. In return periods of 2475 and 475, the percentage increase in acceleration experiences a higher percentage, and the directivity effect is more pronounced in a return period of 2475 compared to 475. The Abrahamson and Silva attenuation relationship was used in the study.

Near-field records have a different nature compared to far-field records due to having a large pulse in the time history, and the existence of this pulse causes significant damage to the structure The differences between near-field and far-field earthquakes are significant, and the characteristics of seismic parameters of earthquake ground motion records obtained in near-fault records are compared with far-field records

In summary, near-field and far-field are two terms used to describe the distance between a microphone and the sound source, and the differences between near-field and far-field earthquakes are significant. The direction of rupture propagation is also important, and the directivity effect can cause pulses with large amplitudes and medium to long periods. Increasing the structural period and return period increases the ground motion acceleration, and the greatest acceleration increase occurs in the 4-second period and 2475-year return period.

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Iranian Journal of Geophysics

Articles in Press, Accepted Manuscript
Available Online from 22 December 2023

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