Three seismograph stations in the area of the quake are needed to find the epicenter.
Since p-waves are faster then s-waves, the p waves reach the seismograph first and then the s-waves.
We use the time between the p and s waves to determine how far the epicenter is from each station. If the distance from one station is 8km than we draw a circle with a 8km radius around that station. We do this for each station.
Where the circles intersect is where the epicenter is.
There are 4 layers of Earth. The inner core at the very center of the earth is a solid, and dense and made of mostly iron with traces of silicon, sulfur and oxygen. Its solid b/c of the pressure from the layers above..
The outer core is liquid and also mostly iron.
Next is Earths mantle. It’s the largest layer and is made of an upper and lower parts.