Effect on the Subsurface Structure Estimation by the Difference in Responses of Two Horizontal Component Seismographs

Receiver function analysis is one of a powerful method to estimate subsurface structure beneath a seismograph. To apply this method, responses of all three component seismographs should be the almost same. However, due to various observation conditions and/or deterioration of sensor, response of each component is sometimes changed. In this study, we investigated the effect of the difference in sensor response on the result of receiver function analyses by using the NIED Hi-net data. N.MHRH, N.TBEH, and N.TSMH stations were selected as examples. At each station, we confirmed that the response of one horizontal component seismograph was slightly different from other components for a period, and that it recovered by the sensor maintenance. Because the difference in time-domain waveforms was very small, we checked it by the spectra of micro-tremor. In this study, we used tele-seismograms with good S/N for all three components. These waveforms were classified the following four groups: (1) All period (Oct., 2000 ~ Jul., 2017). (2) Periods for which the response of one horizontal component seismograph was clearly different from other components. (3) Period in which three component seismographs seemed to have the same response. (4) Same as (3) but excluding the data whose P-wave particle motions were inconsistent with the back-azimuth of the events. For each group, we estimated receiver functions and applied the harmonic decomposition analysis (e.g., Bianchi et al., 2010) to them.