Earthquake epicentres

[Dom Tuk]

How does a sensor in the pacific or scotland deduce where the epicentre of the earthquake is. What type of technology is used (in laymans terms please if possible) and why do some sensor readings in different places differ widely.

[CT]

No one seismograph can determine the epicentre of an earthquake. Fortunately there are many situated all around the world. Different types of waves are emitted from the epicentre, which travel at different speeds. If just one type of wave is measured from three nearby locations then the time taken for the wave to reach each place can be used to find the epicentre. The secondary waves can travel through the earth but not the core. This leaves a shadow zone on the opposite side of the earth where no secondary waves are detected. Primary waves, travel along the surface and are sometimes known as surface waves. The different types of waves arise from different types of motion. The surface (primary) have a perpendicular motion (like water waves). The secondary are compressional (like a slinky spring). It does get more complex than that in depth but those are some of the basics.