P waves are like the lightning, and S waves are like the thunder. The P waves travel faster and shake the ground where you are first. Then the S waves follow and shake the ground also. If you are close to the earthquake, the P and S wave will come one right after the other, but if you are far away, there will be more time between the two. By looking at the amount of time between the P and S wave on a seismogram recorded on a seismograph, scientists can tell how far away the earthquake was from that location. However, they can’t tell in what direction from the seismograph the earthquake was, only how far away it was. If they draw a circle on a map around the station where the radius of the circle is the determined distance to the earthquake, they know the earthquake lies somewhere on the circle. But where?
Photo: Are you prepared? Earthquakes can destroy everything you own in a matter of seconds. This quake, which measured in magnitude, happened at Gizo in the Solomon Islands in 2007. Photo by Andrew Meyers courtesy of US Navy . You could make sure at least one person is trained in basic first aid and ensure that a first-aid kit is easily accessible in your home. You could check that any tall pieces of furniture (such as bookcases or dressers) are screwed securely to the wall so they won't fall on people in a quake. How about putting safety fittings on gas appliances and ensuring that everyone knows how to turn off the gas, electricity, and water in an emergency? You could also swap any ordinary windows for toughened or laminated glass (a bit like bulletproof glass ) to reduce the risk of people being cut by huge falling shards if windows break. Simple precautions like these can help to reduce the risk of people losing their lives or being injured both by earthquakes themselves or the fires and other problems that inevitably follow them. If you live in an earthquake zone, why not spend a few minutes now considering how well prepared you are?