As I understand it, the AltaRock project was actually shut down because they broke too many drill bits. While they were shut down, they analyzed the prospects for earthquakes and discussed with all the concerned parties and decided to abandon the project entirely. They seem to be much better citizens than the oil companies. AltaRock have started up at another site now. See http://www.azocleantech.com/details.asp?newsID=10614.

I think that many of the earthquakes that are noticeable off-site are due to pushing the injection too hard. Of course, as is the case with any commercial enterprise, the management wants to maximize immediate profit, so they push everything. In fact, I read one article that showed that a conventional geothermal plant at The Geysers is being pushed so hard that the reservoir temperature is steadily declining with no sign of leveling off. It reminds me of what sometimes happens in developing oil fields. The operator pushes his production to the point that water invades the reservoir and dilutes oil production or even stops it. Slower production allows the oil/water interface to equilibrate and avoids the problem until the reservoir is more nearly emptied. Some people never learn!

I think that when rules for producing EGS are better learned and regulations and tax policy favor long-term productivity over short term, this over-injection will diminish. Also by using pulsed fracturing and injection in connection with better fracture monitoring, higher injection rates might be achieved without noticeable earthquakes.

A really neat technology to improve and reduce the cost of drilling deep wells in hard rock is being developed by Bob Potter et al. Potter actually invented EGS while working at Los Alamos in the 1970s. See potterdrilling.com for details.