P waves (APEX)
P-waves which are a compression or pressure wave are the fastest seismic waves. As they are the fastest they will reach the seismic station before any of the other seismic waves and be recorded first. Seismologists can use the difference between the arrival times of different seismic waves to calculate the distance and ultimately the location of the earthquakes epicentre. For information on this, please see the related question.
The first waves to arrive at a seismograph station are primary waves, or P waves.
Primary waves are seismic waves and the arrive first after an earthquake occurs.
The distance between a seismic station and the earthquake epicenter is determined from the S-P interval, which is the time difference between the time of arrival of the first P wave and the first S wave.
The first shock wave of an earthquake is known as the P-wave or primary wave. It is the fastest seismic wave and can travel through both solid and liquid materials. P-waves are responsible for the initial jolt felt during an earthquake.
P waves
A seismometer detects primary waves (P-waves) first. These are the fastest seismic waves and are the first to arrive at a seismometer after an earthquake.
A seismometer is the instrument that measures the density of an earthquake, which is done by detecting and recording the vibrations produced by seismic waves. These measurements help scientists determine the magnitude and intensity of an earthquake.
The P Waves. Then the S Waves.
P-waves which are a compression or pressure wave are the fastest seismic waves. As they are the fastest they will reach the seismic station before any of the other seismic waves and be recorded first. Seismologists can use the difference between the arrival times of different seismic waves to calculate the distance and ultimately the location of the earthquakes epicentre. For information on this, please see the related question.
They are given this name in seismology because they are the fastest travelling of the seismic body waves released by an earthquake. Because they are the fastest, they are detected by seismometer stations first. Hence P for primary wave.
Triangulation. First, they calculate the time between the first and second - primary and secondary - seismic waves created in an earthquake and use this information to determine how far the seismometer is from the epicenter of the earthquake. A circle is drawn around the seismometer so that it is in the center and the radius is equal to the calculated distance. Using this information from three different seismometers, two more circles are drawn and the intersecting point of the three circles is where the epicenter of the earthquake is located.
The first waves to arrive at a seismograph station are primary waves, or P waves.
Primary waves are seismic waves and the arrive first after an earthquake occurs.
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. 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 distance between a seismic station and the earthquake epicenter is determined from the S-P interval, which is the time difference between the time of arrival of the first P wave and the first S wave.
3.5 minutes after the earthquake.