If the World Trade Center only measured just over a 2M, then how could skiers affect the seismo? And remember that deal in England where thousands of children tried to cause a mark on the scale...Unless some idiot put the machine out of bedrock and up a bit...or..and this one always fools me...it does look a bit like wind...but wind is a tad more eratic. I get calls on areas near Shasta about wind on the seismo...So your question is really valid...If wind can cause action then why not a skier...Why not ask Charles what he thinks...Only reason I say Charles is that he is so open to alternatives as youknow..