Question

How many seismograph stations are needed to locate the epicenter of an earthquake?
(A) $4$
(B) $2$
(C) $3$
(D) $9$

Answer 1

A seismograph is a device that calculates the magnitude and other properties of an earthquake. A seismograph station is a facility that records the oscillations of the earth's surface caused by earthquakes and processes the data collected.

Complete step by step answer:
In theory, at least three stations are required to determine the epicentre of an earthquake. The epicentre can then be determined on paper using the three circles method (or triangulation) within acceptable error limits.
For the same earthquake, we'll require seismograms from three stations (say, A, B, and C).
Calculate the difference between the arrival times of the P and S waves (say $3$ , $4$ , and $8$ minutes, respectively)at each of the three stations.
Now, for each P-S arrival time, we utilize the global travel-time curve to calculate the epicentral distance. As a result, each station will have three epicentral distances.
At each station location, we use the compass to draw a circle of length proportional to the epicentral distance.
Hence we need $3$ seismograph stations to locate the epicenter of an earthquake so, option C) $3$ is the correct option.

Note:
You can get a rough picture of the earthquake's geographical quadrant from just one station. It's not possible with two because one of the junction points is usually unsuitable for the event. There are three elements used in seismometers to determine simultaneous movement in three directions which are up-down, north-south, and east-west.