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PROPOSITION OF A NEW BASELINE CORRECTION METHOD AND COMPARISON WITH DIFFERENT CONVENTIONAL SCHEMES

Fatemeh Mehrabi

Abstract

It is shown by experience that direct double integration of strong motion data with the aim of generating earthquake displacement records usually leads to unrealistic values of residual displacements even for earthquake s with moderate magnitudes or at far epicentral distances. The appearance of veloc ity and displacement records suggests that changes in the zero level of acceleration are responsible for these drifts. Therefore, in order to calculate real displacements, baseline correction seems consequential. This article illustrates the effect of different conventional baseline correction schemes on amplitude spectra for a couple of earthquakes of Iran. In addition, a new scheme is proposed in which the velocity data are first baseline corrected in the time domain using a sliding window and fitting tec hnique, and the derived acceleration is processed in the frequency domain using a fourth order ba nd pass Butterworth filter. The acceleration data are then integrated to obtain the real velocity and displacement. Affecting the synthetic parameters of accelerograms (PGA, PGV, etc.), the ability to attenuate the artificially produced long period oscillations before the onset of the earthquakes and independency on record length are among the features of the new scheme. The feasibility of the proposed approach is as sessed using severa l examples. Finally, comparisons are made between the results of the proposed scheme and conventional procedures.

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DOI resolver: doi.org/10.5593/sgem2011/s06.118

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