Validating applicability of strain data calibrated in geodetic range on the seismic frequency band by examining Rayleigh wave amplitude ratio

Abstract

Although borehole strain observatories provide useful information about crustal deformation, they need to be calibrated because their highly sensitive observations are affected by structural heterogeneity around the sensors used for settlements. The Geological Survey of Japan developed a strain observation network in southwest Japan to monitor slow-slip events in the Nankai Trough. In this study, the vertical axial strain data of this network as well as the horizontal strain of two newly constructed stations were calibrated using the method used in a previous study. Although this calibration was performed in the tidal frequency band, this study confirmed that the calibration is also valid in the frequency band of seismic surface waves at ~ 0.01 Hz. This fact enables us to use strain data not only for geodetic analysis of crustal deformation but also for the analysis of surface waves from moderate regional earthquakes. This study shows that synthetic strain waveforms are consistent with observed ones, suggesting the usefulness of strain data in centroid moment tensor analysis to improve the resolution of seismic moment tensors.