Hi Kids, In one of my recent letters, I described a earthquake last Saturday. I have attached 2 pictures of the graph from the Mount Erebus Observatory of the event from last Saturday. STRIP2.JPG is a closeup of the event in STRIP1.JPG. The charts run on a big drum, and the paper is changed every day. The drum turns one revolution every 30 minutes, and the pen moves over little, creating the parallel horizontal lines. Every minute, the pen makes a tick, and that is the vertical lines seen in the charts. STRIP2.JPG shows about 2.5 minutes of the big quake. Also on some other lines you can see some minor vibrations.
As seen in the STRIP1.JPG, the event started big, and slowly tapered off. You can not see the whole event, but it lasted for about 17 minutes.
David Hess NK3T