Earthquakes in Oklahoma influenced by Humans?
The sudden and recent occurrence of multiple earthquakes in Oklahoma is due to a widespread redistribution of stresses within the ground, particularly at depth.

Installing large pipes underground for storm water, waste water, or potable water or even digging a basement under every house in an entire city will only cause a very minor localized redistribution of ground stresses, near the Earth's surface. Such minor redistributions of stresses will not lead to earthquakes.

As Blaydes states, injection of fluids and fracking will induce additional stresses and they can also lead to faults and ground fissures becoming lubricated and thus prone to movement, resulting in earthquakes.

Removal of a liquid from an underground reservoir, oil or water, can have an adverse impact. If the reservoir is naturally pressurized, tapping the reservoir will reduce its pressure and the affect that has on the surrounding rock.

Depending on the circumstances, releasing pressure can unlock rock, allowing it to move. It's a bit like having a number of blocks of lumber clamped together by a vice a or a clamp. Provide enough stress (clamping force) and everything is held together nicely. Too much stress and the blocks become damaged due to the strength properties of the individual blocks. Not enough stress and the blocks become free to move relative to one another.

It is well documented, particularly in the US, that removal of water and oil from underground reservoirs can cause surface subsidence. In the case of the Lost Hills and Belridge oil fields in California, subsidence rates of up to 40 mm/day (greater than 400 mm per year) were measured. In the Wilmington oilfield at Long Beach, California, an area 50 square kilometres subsided. In the centre of the subsidence area the maximum subsidence was 9 meters. 

The removal of liquids from underground reservoirs results in a reduction of fluid pressure which causes the pore spaces to close and the sediments to compact, resulting in subsidence. As the sediments compact the rock above it also subsides. Under certain circumstances, such ground movements can induce earthquakes.

In Oklahoma's situation, oil pumping, fracking and fluid injection into oil wells are very likely candidates for the causes of earthquakes experienced there.