All the news is full of the big OK injection reductions. They are going to cut injection by 40% from 2014 levels. What they don't say is that injection is already down a half from 2014 due to oil and gas prices, and the earthquakes keep coming.
They have to 'upgrade' what they inject. They used to inject deep water from wet oil wells. As long as that water had percolated up from the Precambrian, they they could inject all they want. As soon as they started washing the old oil plays with fresh water they had earthquake trouble. Oil and gas fracking all use fresh water.
To the deep Precambrian, fresh water is like a powerful acid. Nobody seems to know that, but it is so easy to test in a lab. This will not happen, and also nobody will map the Precambrian with old seismic reflection data tapes. That is why this all so much fun!