Comparative analyses of records by seismic intensity instrument with strong ground motion records and seismograph stations records: Taking the M_L4.5 Changli earthquake of Hebei Province for an example

Based on seismic records of Changli M_L4.5 earthquake in Hebei Province, by analyzing two groups of waveforms and comparing seismic noise characteristics of seismograph station, strong ground motion station and seismic intensity instrument (SII) station, this paper acquires basic understanding of each kind of these stations, especially the SII station, such as the ability to record micro-earthquakes. The results show that, in certain frequency band (1--10 Hz), seismic waveforms are quite similar for both the SII station and the strong ground motion station or the seismograph station, but large differences appear in mid-long period part. For the same frequency band (0.1--10 Hz band-pass filtered), velocity history and displacement history that are integrated by the SII station data have good correlations and coherences with those from seismograph stations and strong ground motion stations, suggesting that the SII records have certain integrability to some extent. The noise levels of SII stations are far beyond seismograph stations and strong ground motion stations, normally are instrument noise without micro-tremor at all. As a result of only a 16 bit A/D convertor applied, the precision of sampled data is limited and then the accuracy of seismic phase picking will be adversely affected. In conclusion, we think that SII stations are more suitable for moderate to large near-field earthquakes monitoring.