Ground motions induced by strong, distant earthquakes may contain extremely long-period seismic waves that have a dominant period of up to 10 s. In general, these long-period seismic waves have small amplitudes and do not endanger the safety of building structures and civil infrastructures. However, they may bring unexpected shutdown of some vibration (displacement)-sensitive equipment (such as the wafer scanners in high-tech fabs), which can cause production loss. In this study, seismic waveforms collected from broadband seismometers distributed in Taiwan were used to investigate the ground motion characteristics of the collected distant earthquakes (with an epicenter distance of over 1000 km). The time-variant dominant frequency was extracted using moving window wavelet packet transform to monitor significant long-period seismic waves from the preevent data of each seismic event. The slope of the Arias intensity and the slope index of the recorded seismic waves were also developed to detect the potential accumulation of vibration energy increasing with respect to time and amplitude. The proposed index was used to detect the features of significant distant earthquakes, and it provides a mechanism to prevent unexpected shutdown of displacementsensitive equipment. Finally, the proposed approach is discussed in relation to the damage severity of high-tech fabs.

The precision tools equipped with active vibration isolation platform in high-tech facilities are sensitive to low-frequency vibration. Currently, there are neither standards nor rules to select the time period of vibration data for conducting the spectral analysis of low-frequency vibration, and none of the analyses can be used to compare and discuss the differences of spectral amplitude generated by the selection of different time periods. Therefore, to estimate the amplitude of low-frequency vibration, the spectral analysis at low-frequency range is crucial. This paper is to elaborate the spectral analysis procedures on various band widths by using zero-padding on the vibration signal in low-frequency band. The mechanism not only facilitates to obtain more reliable result but also to lay a common base for comparison from different user. Finally, the in situ measurement data, including high-speed train-induced low-frequency vibration, are used to exemplify the length of time period affects the results of spectral analysis, either on narrowband or one-third octave band analysis.

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