I have a working leaflet map that is showing earthquake data from http://earthquake.usgs.gov/. I'm trying to figure out the "right" way to calculate the radius of the circle for an earthquake given its magnitude (and possibly depth).
The circle is being created with
L.circle(latlng, radius);
(where radius is in meters). The previous map developer did this:
var radius = 30000 * magnitude;
Which looks good on a map but doesn't seem right – he just made up a number to make it look decent. I googled and found two other earthquake maps using leaflet and they did this:
var radius = Math.sqrt(Math.pow(10, magnitude))/50000);
and the other did this:
var radius = Math.pow(2, magnitude);
but both of those draw very tiny circles on the map. As an example, if the magnitude is 5.0, I would get radii of 150000, 1.414, and 32, respectively.
So, my question… is there a standard/accepted formula for drawing an earthquake circle on the map using the magnitude (and maybe the depth)?
UPDATE: I found one more:
var radius = (Math.exp(magnitude/1.01-0.13))*1000;
which for a magnitude of 5.0 gives a radius of 124026 meters (and "looks" good on the map). Barring any insights from the community, I may just go with this one.
Best Answer
The question is, what is your radius trying to represent. I get the feeling you don't really know. Is it meant to be the distance at which you would physically feel the quake? That's hard to measure.
Is it the energy of the quake? Then you would want a scale that isn't just linear - because each +1 unit of magnitude is around 30x stronger than the previous.
Plus, I know that earthquakes don't pass through the same land material types at the same rate, so if you want to be picky, the "radius" wouldn't be circular anyway.
In short, if you're not trying to show a specific geological feature, then I'd say just go with what looks good!