It is therefore supposed that one can measure the building up of the stress by the slight deformation prior to a quake. However, as a means to predicting earthquakes, this method has been entirely unsuccessful. The ground does distort on occasions, but not by any unusual amount before an earthquake. The evacuation of Haicheng two hours before a devastating quake is an example of a successful prediction, and it was based mainly on gas effects such as a cloud of warmer air and fog developing above the known faultline, strange and nauseating smells and changes in groundwater levels. The same effects have been mentioned in very many of the ancient records.
Gases can indeed have a lot to do with earthquakes.
A large volume of gas entering the crust of the Earth from deeper levels and at a high pressure, will greatly change the mechanical properties of the rock. Pore-spaces will be inflated, and the overburden weight of the rock will be effectively relieved by the pressure of the gas. The great weight of the overburden would normally have resulted in high internal friction, opposing any slippage at all but the shallowest levels. But with gas effectively bearing the overburden, slippage can occur much more easily. Much smaller values of stress in the rock will then be sufficient to cause a quake.