The amount of pressure necessary to move tectonic plates with "wastewater" simply cannot be achieved. Also, The wastewater will take the path of least resistance once it is outside of the influence of the pump. Forcing itself between bedrock isn't that place.
Well, while that's true, it
is possible for the water to act as a lubricant, or to facilitate slippage between strata by breaking up their physical interlocking. However, the fact that the earthquakes originate at a far deeper level than the injection occurs would seem to me to rule that out, I wouldn't think the injected material could migrate miles downward into progressively higher pressure zones.