Keywords: stochastic model, ground motion, generation, point source, Zarand, response spectra.

Estimation of destructive ground motions from a future event is a fundamental engineering step to anticipate the possible socio-economic damage. Such damage depends to a great extent on the dynamic characteristic of the strong motion and local site conditions. The realistic simulation of strong motion and the study of local site effects are therefore of prime importance in earthquake engineering particularly for essential structures such as oil industrial structures. The procedure of generating strong motions becomes more important for the regions with a lack of sufficient information. The main goal of this research work is to simulate strong motions consistent with the source-path-site, to be used in linear and non-linear analysis of structures.

Ground motions are estimated by identifying the major regional faults and propagating seismic waves generated at these potential sources of the site of interest. While the gross path parameters, such as geometric spreading and inelastic attenuation, can be estimated quite well on average from either empirical or theoretical models, there is much debate as to the nature of the seismic source radiation.

A seismological model originally developed by Brune [1] and further developed by Atkinson et al. [2,3], identifies the important factors affecting the properties of earthquake ground motion and distils these factors into a few key parameters. The Fourier spectrum specified in this model is expressed as the product of a source factor, a geometrical attenuation factor, a whole path attenuation factor, and the factors representing site effects. The source factor has been found to be consistent with the Fourier transform of the shear wave predicted by the point shear dislocation theory [4,5].

In this paper, we utilized a stochastic model to simulate the strong motion characteristics associated with the 22 February 2005 Zarand main shocks (in Kerman province, southeast part of Iran). The strong ground motion of the Zarand earthquake was recorded at twenty-seven stations around the epicentre by the Building and Housing Research Center of Iran (BHRC), with a magnitude of and a seismic moment dyn-cm. The maximum measured peak ground acceleration recorded at the station located 28 km distance from the epicentre, reached 0.323g.

Based on the equivalent point source model and the selected parametric values, the desired acceleration amplitude spectrum is calculated.

After selecting and, or calculating the appropriate seismological parameters, the simulated peak ground acceleration time history and corresponding elastic response spectra (PSa, PSv, PSd ), were validated by comparison with those of the observed records. It was found that, the observed and synthesized ground motions as well as the elastic response spectra are satisfactorily similar which reflects the efficiency of the technique and the reliability of the model parameters. Additionally, the sensitivity of the PGA against the anelastic attenuation path-frequency-dependent quality factor, , was also studied. The results showed that, the variation of the quality factor () does not have a strong effect on the response spectra, and hence could be used for simulating earthquakes in Zarand region in the future. Regarding the simulation results, it could be claimed that, unless the factors for the California region [6], the results obtained from the other factors are in a comparable range between the observed and the simulated values of the peak ground acceleration and the response spectra.

The results of this study, confirm the reliability of the incorporated model parameters, consequently it can be used for the prediction of strong motions to be used in the hazard analysis of specific sites such as those for the industrial oil company in the Zarand region of Iran.

1

Brune, J.N. "Tectonic stress and the spectra of seismic shear waves from earthquake", J. Geophys. Res. 75, 4997-5009, 1970. doi:10.1029/JB075i026p04997

2

Boore, D.M., "Stochastic simulation of high-frequency ground motion based on seismological model of the radiated spectra", Bull. Seism. Soc. Am. 73, 1865-1894, 1983.

3

Hanks, T.C. and McGuire, R.K., "The Character of High Frequency Strong Ground Motion", Bull. Seism. Soc. Am. 71, 2071-2095, 1981.

4

Beresnev, I.A. and Atkinson, G.M., "Modeling finite-fault radiation from the n spectrum", Bull. Seism. Soc. Am. 87, 67-84,1997.

5

Atkinson G.M. and Boore, D.M., "Ground-Motion relations for Eastern North America", Bull. Seism. Soc. Am. 85, 17-30, 1995.

6

Atkinson G.M. and Silva, W.J., "An empirical study of earthquake source spectra for California earthquakes", Bull. Seism. Soc. Am. 87, 97-113, 1997.

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