I remember reading about this geothermal project being cancelled due to concerns over (relatively) small seismic events caused by the drilling. Have there been any instances of, or reasonable scientific cause to believe a major seismic event might happen due to geothermal drilling?
Short answer: yes.
Longer answer: There's a statistically significant positive correlation between EGS and seismic activity.
Longer, peer-reviewed answer: http://escholarship.org/uc/item/0t19709v
BTW, the path I used to find that was
And no, I didn't read the paper, I'm (uncritically) assuming that Wikipedia wouldn't get the cite backwards on something that obscure. ;-)