 No significant historically recorded earthquakes have occurred in Houston, but researchers do not discount the possibility of such quakes having occurred in the deeper past, nor occurring in the future.Land subsidence has occurred across Greater Houston, primarily due to the pumping of water from subsurface aquifers (see Groundwater section).This subsidence may also be associated with slip along the faults; however, the slippage is slow and not considered an earthquake, in which stationary faults must slip suddenly enough to create seismic waves.