Which type of wave can be used to determine the location of an earthquake's focus?

Answer 1

s and p waves

Answer 2

First of all, seismic waves caused by earthquakes often travel far, and (depending on the magnitude) can be registered by seismometers sometimes thousands of kilometers away.

This means that most earthquakes are at least registered by 3 seismometers, mostly by more. This is essential.

To determine the distance of an earthquake from a seismometer, you need to take the time between the first arrival of the P-wave (primary wave, a wave that moves faster), and the S-wave (secondary wave, moves fast, but significantly slower then the P-wave). As the S-wave travels slower, the amount of time between the arrival of both seismic waves indicates how far from the source you are. Now you can draw a circle on the world map with all the points being that distance from the seismometer. We still don't know where the epicenter is, though. So we take a second one, repeat the process, and draw the second circle. Typically, there will be two points of intersection. The epicenter is one of these points. So we need a third one too. Repeat the process with a third seismometer, and you will have one point left. That is the epicenter of the earthquake.

In practice, you will have more then just 3 seismometers on your hands, so you can very accurately determine the epicenter.
To locate an earthquake, you need the data from at least three seismometer stations.

The process is known as triangulation and is described in more detail below.

The seismometer records the P and S-wave arrival times. P-waves travel faster through the earth than S-waves and so they arrive at the seismometer station before the S-waves and are recorded by the seismometer first.

The difference in arrival time between the two types of seismic wave can be used to calculate the distance of the earthquake's epicentre from the seismometer.

DE = DeltaT x (VP - VS) / (VS x VP)

Where:

DE = Distance to epicentre (km)

DeltaT = Difference between P and S-wave arrival time (s)

VP = P-wave velocity (km/s)

VS = S-wave velocity (km/s)

This can then be plotted on a map, by drawing a circle with a radius equal to the distance to the epicentre around the seismometer station. This is then repeated for the other two seismometer stations and the point where the three circles intersect is the location of the earthquakes epicentre.

The above procedure is commonly automated using computers and numerical techniques so that a large number of differing seismic episodes can be processed efficiently.

It should be noted that this is an imperfect process as a number of assumptions must be made about the material through which the seismic waves travel in order to estimate their speed.

Answer 3

Seismic waves, particularly the P-waves and S-waves generated by an earthquake, can be used to determine the location of an earthquake's focus. By analyzing the arrival times of these waves at different seismograph stations, scientists can triangulate the epicenter and depth of the earthquake focus.

Answer 4

They use seismic body waves - specifically the P and S-wave to find an earthquake's epicentre.

Answer 5

Seismic waves can be used to determine the location of an earthquake focus. These waves are triggered by tectonic plates.