Fig. 9

a Monthly and cumulative numbers of Hi-net events up to the end of 2019. The histogram indicates the number of Hi-net events in each month. The red line indicates the cumulative number of events since October 2000. b Magnitude distribution of monthly Hi-net events. The color scale denotes the monthly Hi-net events within each bin with a magnitude width of 0.1. c Spatial (left) and spatiotemporal (right) distribution of tremors. The red circles denote tremors. In the right panel, VLFEs and SSEs are shown by the blue diamonds and green lines, respectively. d Monthly and cumulative sizes of Hi-net waveform data. The histogram indicates data size of Hi-net events for each month. The red line shows cumulative data size since October 2000. e Monthly and cumulative numbers of F-net moment tensor solutions. The histogram indicates the number of F-net moment tensor solutions. The colors indicate the magnitude range. The red line shows the cumulative number of F-net moment tensor solutions since January 1997. f Temporal distribution of moment magnitudes of F-net moment tensor solutions. The red circles denote moment magnitudes