Fig. 1
source is used at the hypocenter. The 2–50 mHz and 2–30 mHz band-pass filters are applied to the horizontal and vertical components, respectively. The contour lines are drawn every 1 nm/s2 and 0.5 nm/s2 for the horizontal and vertical components, respectively. The yellow star indicates the epicenter of the event. a Horizontal east–west (EW) component. The green dots represent the Hi-net stations where the EW component of the tiltmeter records is used for stacking, and the black dots represent the other stations. b Horizontal north–south (NS) component. The green dots represent the Hi-net stations where the NS component of the tiltmeter records is used for stacking, and the black dots represent the other stations. c Vertical up–down component. The green triangles represent the F-net stations where the vertical component of the broadband seismometer records is used for stacking, and the black triangles represent the other stations
Spatial amplitude distribution of the synthesized three-component pre-P gravity signal from the 2011 Tohoku-Oki earthquake at \(t={t}_{\mathrm{P}}^{\mathrm{theo}}\). The simulation method of Zhang et al. (2020) is used, and a GCMT point