Animation example displaying earthquakes

This is an example for the animation function displaying animated earthquakes from the last 30 days. It uses the basemap toolkit and reads information from http://earthquake.usgs.gov/earthquakes/feed/v1.0/csv.php

The animation is made using a scatter plot. Each earthquake is shown as a growing and fading filled disc. In the example, there are 50 simultaneous anytime. 

The use of the TkAgg backend is necessary on OSX.