I was wondering what is the equation that gives the values in a Jefferys – Bullen Table? Specifically, what’s the equation for finding the distance (or angle) from a seismic station to the epicentre of an earthquake using the difference in travel times between S and P waves as recorded by the station? Oh also, more of a math question, but I’ll use it for triangulating the location of the epicentre: How would one go about finding where 3 circles on the surface of the Earth intersect (if you know the radius of each circle and their coordinates on the Earth) mathematically? My assignment is really to do this by estimating what the distance to the epicentre would be by looking up values on a Jefferys – Bullen Table and then triangulate them by drawing circles on one of those big globes that you can use chalk on. As you can imagine, it’s a very messy process. I already did it and figured out where the epicentre was; I just want to know how to do it mathematically. Thanks!