Transcripts of referenceTravTimeTutorial
In the previous screencast, we looked at how to figure out the actual path length traversed by the P wave in the case of a homogeneous mantle. So let me just write that again. "x" - that's the path length is twice the radius of the Earth multiplied by the sine of half the angular distance in between the two points. So, x is the path that we found, the radius of the earth is 6371 km, and then delta is just the surface distance in degrees. We wind up here with an answer that's in kilometers. But what I asked you to do was to make travel time curves. So this isn't there yet because we just have a distance, not a time. In order to get the travel time all we have to do is divide this distance x by the speed. And I told you to use some constant mantle speeds. For example, if we use 8 km/s, All we're doing is dividing x by 8. The units work out because x is in kilometers and then 8 is km/s so the travel time is in seconds. That's what we want, that's good. Now, here's how I would go about constructing my travel time curves. I would ignore the actual data we have because these are just reference lines. So I would just start with a series of deltas. LIke, 0, 5, 10, 15, blah blah blah up to 90 degrees or something. And then I would just calculate the travel time for each one, which is easy to automate. All you do is plug in these values of delta in the equation up top. When you get x you divide that by the constant velocity, and you get your travel time in seconds. Now you can make a plot. It's just plugging in, that's all there is to it.