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Seismic records collected from earthquake with large magnitude and far distance may contain long period seismic waves
which have small amplitude but with dominant period up to 10 sec. For a general situation, the long period seismic
waves will not endanger the safety of the structural system or cause any uncomfortable for human activity. On the
contrary, for those far distant earthquakes, this type of seismic waves may cause a glitch or, furthermore, breakdown to
some important equipments/facilities (such as the high-precision facilities in high-tech Fab) and eventually damage the
interests of company if the amplitude becomes significant. The previous study showed that the ground motion features
such as time-variant dominant frequencies extracted using moving window singular spectrum analysis (MWSSA) and
amplitude characteristics of long-period waves identified from slope change of ground motion Arias Intensity can
efficiently indicate the damage severity to the high-precision facilities. However, embedding a large hankel matrix to
extract long period seismic waves make the MWSSA become a time-consumed process. In this study, the seismic ground
motion data collected from broadband seismometer network located in Taiwan were used (with epicenter distance over
1000 km). To monitor the significant long-period waves, the low frequency components of these seismic ground motion
data are extracted using wavelet packet transform (WPT) to obtain wavelet coefficients and the wavelet entropy of
coefficients are used to identify the amplitude characteristics of long-period waves. The proposed method is a timesaving
process compared to MWSSA and can be easily implemented for real-time detection. Comparison and discussion
on this method among these different seismic events and the damage severity to the high-precision facilities in high-tech
Fab is made.
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