[Evilhomer]

I finally decided to be math geeky, so here goes:

Binomical distribution GIVEN 1 site is earth (when we entered province // no searches done).

sites - probability
0 - 0.000
1 - 0.216
2 - 0.432
3 - 0.288
4 - 0.064

Chance of finding one or more astral sites using a level 9 search spell (assuming all types of sites have the same probability, not true but whatever...)

P(2)*(chance of 1+ astral site=1/8)+P(3)*(chance of 1+ astral site=15/64)+P(4)*(chance of 1+ astral site=169/512)

=

0.143 (or 14% if you wish)

So the chance decreases, but not by as much as reported by valkenbear. Same calculation provided that we have searched using gnome lore (and found 1 site) will follow..

*Note the "chance of 1+ astral site" changes, being 1/8 in the first bracket and (1/8*7/8)+(7/8*1/8)+(1/8*1/8)=15/64 in the second bracket, and so forth