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Figure 9. Epicentres of recorded earthquakes.

6 RECORDED EVENTS

Table 2 shows the seismic events recorded by the monitoring system, and gives information about the earthquakes. The epicentres of the recorded earthquakes are presented on the map of Figure 9.

7 PROCESSING OF STRONG MOTION DATA

The digitised signals were corrected taking in to account the dynamic characteristics of the accelerometers that have a frequency of 1.38 kHz and damping coefficient Z = 70%.

The acceleration time histories of the earthquake of 08/01/06 for channels 1-14 are presented in Figure 10, respectively. A lowpass digital filter with cutoff 25 Hz and a highpass with cutoff 0.7 Hz were used for data processing.

Total acceleration response spectrum (Nigam, N.C. & Jennings, P.C. 1969) on soil surface for the same earthquake for damping coefficient 5% are shown in Figure 11.

The amplification factor between the maximum acceleration at various locations on the structure and the acceleration on the soil surface of the same orientation is given in Table 3.

The damping coefficient of the first mode is given in Figure 12. The natural period of the first mode was changed during earthquakes as shown in Figure 13.

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