### 6.3 Geographical epicentre-coordinates (localisation by one seismographic station) 1/5

Determining the geographical coordinates of the epicentre means calculating latitude and longitude of the epicentre with the help of results calculated from the data recorded by our three seismographs.

The mathematical idea is as follows (congruence theorem LAL)

Here we see the triangle "North Pole - Station - Epicentre". We already know two destinators of LAL:

- the spherical leg Θ
_{S}(= "Station - North Pole", since the geographical), coordinates of the station are known - the spherical distance Δ from the Station S to epicentre H. (We fixed it in chap. 6.1.)

We finally need a third destinator for the triangle SHN.
In our case it is angle
**α**which is formed by the legs Θ_{S} and Δ