Seismic waves can be measured on a seismograph which records and locates the size of seismic waves during an earthquake event. Seismographs can be used to help predict an earthquake epicentre and they can also be used to help predict future earthquake events by determining which areas are most likely to suffer from structural damage, landslides and soil liquefraction. Seismographs measure the amplitude of the seismic waves by measuring the distance between movement of the instrument and the spring which has inertia in it. The degree of movement between the mass and the rest of the instrument helps geologists and scientists to accurately measure the magnitude and size of seismic waves. Earthquakes are measured on a Richter scale which records the magnitude of the event. The Richter Scale is logarithmic and so each unit represents a 10 fold increase in strength and a 30 fold increase in energy released. So, therefore a magnitude 7.1 earthquake is twice as big as a magnitude 6.9 event. Moreover earthquakes can be measured on a 12 point Mercalli scale which reflects the effects of an earthquake. The more severe the earthquake the more destructive the effects and the higher the score on the Mercalli scale. The scale however relies on individual interpretations of the effects of an event and not everyone will agree on its effects eg degree of ground shaking. Finally an earthquake can also be measured on the moment magnitude scale which is a more up-to-date way of measuring earthquakes by geologists. However the Richter Scale is still used to show the size of an earthquake for the public and mass media. (8)