GEOLOGY

Detailed explanation-1: -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.

Detailed explanation-2: -You need one because the epicenter will be somewhere along that circle. You need three because three is the minimum number of circles that will intersect at one point. It’s not possible to do this with only seismic data.

Detailed explanation-3: -Modern seismometers include three (3) elements to determine the simultaneous movement in three (3) directions: up-down, north-south, and east-west. Each direction of movement gives information about the earthquake.

Detailed explanation-4: -Three seismographs are needed. A circle is drawn from each of the three different seismograph locations, where the radius of each circle is equal to the distance from that station to the epicenter. The spot where those three circles intersect is the epicenter (Figure 13.12).

Detailed explanation-5: -By looking at the seismograms from different recording stations, we can find out the epicentre of the earthquake. The signals arrive first at the closest station and last at the one furthest away. The time difference between the P-and S-waves tells us the distance the earthquake is from the seismometer.