Fig. 9
From: Earthquake-induced prompt gravity signals identified in dense array data in Japan
a Theoretical six-component gravito-gradiograms of the 2011 Tohoku-Oki earthquake synthesized for Kamioka Observatory. Time 0 was set to the event origin time \(t_{\text{eq}}\). b Distribution of prompt gravity gradient changes immediately before P-wave arrival at each location (upper left: \(\ddot{h}_{11}\) component, upper center: \(\ddot{h}_{22}\) component, upper right: \(\ddot{h}_{33}\) component, lower left: \(\ddot{h}_{12}\) component, lower center: \(\ddot{h}_{13}\) component, and lower right: \(\ddot{h}_{23}\) component), where \(\ddot{h}_{ij}\) denotes the ijth component of the gravity gradient tensor (see “Appendix 4”). In these figures, the \(x_{1}\)-, \(x_{2}\)-, and \(x_{3}\)-axes correspond to the directions of east, north, and upward, respectively. The star and the letter K are the epicenter and Kamioka Observatory, respectively. The contour lines are drawn every \(2 \times 10^{ - 13} \, {\text{s}}^{ - 2}\)