There are many ways to predict earthquakes, and those ways could help the world to prepare for and prevent damage. There are ways to predict them for long periods of times (thousands of years), or very short periods of time (possibly decades). One can predict when an earthquake is going to occur by studying the rate at which strain builds up, studying the history of earthquakes in certain places and discovering how often an earthquake occurs in that place, or one can use a seismograph to predict when an earthquake will occur within shorter time ranges. Currently though, there is no way for seismographs to be accurate enough for people to be able to have notice to prevent damage.
One way scientists can predict earthquakes is by using a formula to calculate when and how big an earthquake will be. They need three pieces of data to calculate the formula: how much time has passed since the last earthquake, how much strain was released in the earthquake, and the strain that is currently on the fault line. They use these numbers to calculate how big an earthquake will be and when it will occur.
Another way scientists predict earthquakes is by using a seismograph, but it is meant for more short periods of time. Seismographs record ground shaking onto a graph and scientists analyze the data to predict when an earthquake will occur and how big it will be.
P and S waves have a big effect on what the seismograph displays. The P (primary) waves travel much faster through the earth than S (secondary) waves, but Secondary waves travel much faster than Surface waves. However, Surface waves have no effect on seismographs results. Secondary waves cannot travel through fluids while Primary waves can. Seismographs locate earthquakes by measuring the distance between the Primary and the Secondary waves.
Today's Seismographs are digital and can record a large range of frequencies. A large number of frequencies can also be referred to as Broadband. They are measured by the amount of electric energy needed to keep the mass centered in the housing in the presence of the ground shaking. Today's Seismographs can record large and small signals. Most Seismographs need to be operated in very quiet places because they can pick up low sounds such as 25dB, for example a person talking quietly, and that sound has enough vibrations to cause the results to be changed drastically.
The original Seismograph was invented by Choko in 136 AD. It was made of copper and had eight dragon heads mounted above eight frogs. Each dragon had a ball in its mouth and scientists would tell where and how big an earthquake is by analyzing which balls dropped into the frogs' mouths. In the nineteenth century, European scientists made a different Seismograph. It was operated by electromagnetic suspended mass, or pendulum, within and electric coil. A magnet within the electric coil created a current which could be translated into an electric current. The electric current could be projected onto paper and traced by a needle.
Overall still today earthquakes are very difficult to predict. Predictions are not yet accurate enough today to help the world in prevent damage and deaths. If predictions of earthquakes are accurate enough one day, it could really help society. But until that day, earthquake predictions will not be accurate enough to prevent damage.