Earthquake Table

Earthquakes are a risk to life and cause a lot of damage to buildings and infrastructure. The study of earthquakes is known as seismology.

Most damage is caused by surface waves, known as Rayleigh waves and Love waves. However, the first waves to arrive actually occur under the surface. These waves are called P-waves and S-waves.

P-waves and S-waves travel at different speeds. By measuring the time between P-waves and S-waves, we can calculate the distance from the earthquake’s centre, but not the direction. This means every measuring station will have a radius of possible locations for the earthquake’s centre.

With the help of three measuring stations, we can find where the three circles intersect, revealing the location of the earthquake centre.

After locating an earthquake, nearby cities can prepare for any quakes that will occur in the following days.

Predicting individual earthquakes is difficult, but statistics can be used to estimate the likelihood and frequency of earthquakes in a particular area.

Earthquakes have been studied since ancient times, but the causes of earthquakes remained a mystery.

In 1755, an earthquake almost destroyed Lisbon, Portugal. This event led to the birth of modern earthquake science (seismology). And six years later, English scientist John Michell had determined that earthquakes were waves caused by shifting rock within the earth.

Another English scientist, Richard Oldham, was the first to identify the separate arrivals of P-waves, S-waves and surface waves. Since S-waves do not pass through liquids, Oldham was able to deduce that the Earth contained a liquid core. Further studies revealed that the liquid core contained a solid inner core.

Although predicting individual earthquakes is hard, statisitics can be used to forecast the frequency of earthquakes in a certain area, and the expected waiting time between quakes.

By measuring the difference in arrival times of waves caused by earthquakes, we can determine the centre of the quake and prepare cities nearby for more quakes that follow.

By studying the properties of waves, and how they travel through different material, we were able to determine the interior structure of the earth, and understand why earthquakes happen.

We can work out how far away earthquakes started because waves under the surface travel at different speeds.

You can do a similar experiment the next time there is a thunderstorm. When you see a flash of lightning, start counting the seconds until you hear the crash of thunder. Dividing the number of seconds by 3 gives the distance of the storm in kilometres. (Divide the number of seconds by 5 if you want this distance in miles).

This works because sound travels at a speed of 330 m/s.

When you see another flash of lightning, count again. Is the storm moving towards you or away from you?