Fig. 2

Velocity structure models used in this study. Gray thick lines indicate P- and S-wave structure models used for the back-projection analysis. The model is used by Kyushu University for routine analysis of hypocenter determination in this area. Red and blue lines indicate P- and S-wave structure models used for calculating synthetic waveforms. The model is composed of the velocity structure obtained by discretization of the structure model by Kyushu University, and the velocity structure of sediment layers around station OIT009 by Koketsu et al. (2008)