To capture the seismic precursor information and assess the performance of pendulum inclinometers in the Chengde area,the noise spectrum characteristics of three VP-type vertical pendulums and one horizontal pendulum inclinometer were studied using power spectral density analysis methods.The study results show that under normal conditions,the main background noise recorded by the four instruments is the low-frequency natural environmental noise below 0.2 Hz;rainfall events mainly affect the low-frequen-cy band below 0.2 Hz;pendulum instruments can record seismic waves well,with local earthquakes showing more high-frequency components,and distant earthquakes dominated by surface waves;seismic events can lead to a significant increase in noise in the 0-0.3 Hz frequency band;during instrument calibration,low-frequency noise will significantly increase.
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