Induced events are exactly the same as natural ones, except that the trigger for the movement is human activity, rather than a gradual build-up of geological pressure over time. The seismic shock waves are still generated by movements of rock, but the cause may be blasting in a local quarry, a low-flying helicopter or the testing of a geothermal well. In the case of geothermal projects, ground movement can be caused by water pressure helping to unstick the rock along the faults or small fractures.