Fig. 3

a Spatial distribution of clusters derived from GPS stations in Southwest China. Different colors indicate 49 stations contained in 12 clusters, and the remaining 9 stations are shown as black dots. b Spatial distribution of annual amplitudes and phases derived from GPS height time series in Southwest China. Arrow length represents the magnitude of annual amplitude, and arrow direction shows the annual phase. The azimuthal angle of each vector (counter-clockwise from the East direction) represents a positive phase of annual variation. Numbers in each circle mean the cluster code, and symbol “+” means the selected station is determined as with local abnormal signal in the above clustering process