Script effetto terremoto

script language="JavaScript">
<!--Inizio script prelevato da http://allrevolution.forumfree.net/ //-->
posi = 0;
function Vibre()
{
if(posi<100)
{
if(posi/2 == Math.round(posi/2))
{
X = Math.round(Math.random()*40)-20;
Y = Math.round(Math.random()*40)-20;
window.moveBy(X,Y);
}
else
window.moveBy(-X,-Y);
posi++;
tempo=setTimeout('Vibre()',10);
}
}
Vibre()
</script>