It has internal processes that are in motion. Huge forces produced by the internal processes of the earth are constantly pushing and pulling at the earth's Crust. These forces produce stress within the solid rock layers. Earthquakes are vibrations of the earth caused by a rapid release of energy. Seismology deals with the measurement of these ground vibrations.
Seismographs consist of inertia member , transducer , and a recorder .
Here is an example of the readout from 3 small earthquakes. Surface Waves shakes the ground in a transverse mode and travels much slower than S-Waves. A rather subjective scale also exists called the Modified Mercalli Intensity Scale . The best scientist can do in predicting earthquakes is to assign probabilities. An earthquake can be more or less likely to occur in a certain region during a specified time.