Calculation of the sensitivity of the in-situ seismograph using the collocation test

The accuracy of ground motion restored from seismic records is directly determined by the accuracy of seismograph sensitivity. To further address this issue, we deployed multiple sets of reference seismographs at four Chinese National Digital Seismographic Network stations and estimated the relative sensitivities of the in-situ seismographs at these stations by the correlation technique using earthquake events and micro-seism noise, respectively. Results show that both earthquake events and micro-seism can be used as stable signal sources to estimate the relative sensitivity of the in-situ seismograph reliably for all three components including vertical, northsouth and east-west and both the two methods exhibit a high consistency. For the in-situ seismograph which cannot be interrupted, the method proposed in this paper is an effective way to estimate the sensitivity of the seismograph in service. At four seismic stations tested, there are multiple components showing sensitivity errors larger than 3 % at the Mengcheng and Jiujiang stations, and the sensitivity errors of the vertical and north-south components at the Mengcheng station are even close to 10%. Analysis suggests that the further work focused on the sensitivity investigation of stations from Chinese National Digital Seismographic Network is necessary and urgent, which would be significant for the improvement of seismic data quality in Chinese seismic observations.