Oklahoma looks pretty flat today, but it is the home to some of the oldest mountains in the country, they've just all been eroded off at the top. Below the ground level, there is still some pretty complicated geology with some very big faults. These faults have not been very active in recorded history, but recently we have been seeing more activity. The best theory about the cause of these earthquakes is that the faults have been lubricated by the injection of "waste water".

Waste water wells are drilled into deep rock formations for the purpose of disposing of water that comes from producing oil and gas wells. When an oil well produces oil, it also produces a large amount of water. This water is pretty nasty stuff and we don't want to keep it on the surface, so it is injected back underground. If the disposal wells are drilled into faulted zones, the rock is more fractured and can absorb more of the waste water. If the faults are prone to slipping, the water lubricating the fault helps it to slip sooner rather than later.

Best Regards,
Ted