Time dependence of total velocity integrated intensity (line area) and velocity spread for each association from our VERA observations. The first and second panel shows respectively the line area for associations containing increasing and decreasing trends at the onset of the burst. The third panel shows the velocity spread for each association over time. The colours for the third panel are the same as in the legends in the first two panels. The red and black lines indicate the date of the onset and peak of the burst, respectively.