Fig. 1
From: Earthquake-induced prompt gravity signals identified in dense array data in Japan
a Model prediction of the prompt gravity perturbation \(\left( {\delta \varvec{g}^{\text{H}} } \right)_{z}\) (vertical component with upward positive) of the 2011 Tohoku-Oki earthquake for Kamioka Observatory. We used the infinite homogeneous Earth model of Harms et al. (2015), and no filter was applied. Time 0 was set to the event origin time \(t_{\text{eq}}\). The P-wave arrival time on the gravimetric record is 05:47:32.4 UTC (68.1 s after \(t_{\text{eq}}\)). b Distribution of the prompt gravity perturbation \(\left( {\delta \varvec{g}^{\text{H}} } \right)_{z}\) immediately before P-wave arrival at each location. The contour lines are drawn every 10 nm/s2. The star, the letters K and M, the red triangle, and the small dots indicate the epicenter, Kamioka Observatory, Matsushiro Observatory, the 71 F-net stations, and the 706 tiltmeter stations, respectively