text:  But they don't really tell you where or how big. And so you look at your springs or your, if you have hot springs, they may change their temperature. Often over a period of months prior to quake, the volume of water will decrease and the temperature will decrease. And then suddenly the quake will hit and you'll find the temperature is 10 or 20 degrees warmer and maybe full of H2S gas or maybe releasing a lot of radon gas that could have been detected days in advance of the earthquake. All right. The ground may tilt.