One thing I forgot to add about the shale gas exploration in the case that started the thread...
I don't know the situation in Texas ...
-wiki only mentions 2 larger than 6 Richter scale earthquakes last century and I don't know how far they are from the wells-
but in the case of the Pungesti exploration , it is in a 100 km range from the most active earthquake center in my country which triggered 5 7+ Richter scale earthquakes last century.
Although there are some places in the world that it is
thought that the edges of tectonic plates sit, this is not a 100% known fact. Also there are some places where earthquakes are more common, but in reality earthquakes can happen in any place at any time.
If fracking is done in places where the risks of earthquakes is greater, then more precaution can be taken to protect against the effects of earthquakes; similar to what is done to buildings in these kinds of places.
Trust me , the so called Vrancea area is at the edge of 3 not two tectonic plates.
Vrancea seismic zone is located in Romania at the South-Easter Carpathians bend, where at least three major tectonic units are in contact: East Europen Plate, Intra-Alpine Plate and Moesian Plate. The seismicity of the Vrancea zone consist of both crustal and intermediate-depth earthquakes. The crustal events are moderate (M w ≤ 5.5) and generally occur in clusters in space (the subzones Râmnicu Sărat and Vrâncioaia, situated in the Vrancea epicentral area and adjacent to it) and in time (main shocks accompanied by aftershocks and sometimes by foreshocks or swarms). Seismic activity in Râmnicu Sărat zone consist of shallow earthquakes with moderate magnitudes M s ≤ 5.2 (Radu, 1979), wich frequently occur in clusters.