We now support compositing vector tiles - allowing me to style different data sources at once as if the base map and earthquake data were all coming from one souce. This vector tile compositing enables Photoshop-like color compositing of ground velocity data against terrain and landuse layers but keeps earthquake layers drawn behind labels to maintain legibility.
The USGS publishes a ShakeMap of every earthquake within minutes of the event. You can take shapefiles from the USGS and drop them right into TileMill 2 - our open source map design studio - to make your own vector tiles and start styling composited maps.
I will be blogging more about compositing vector tile sources in TileMill 2 over the next few weeks. Ping me on Twitter @ian_villeda if you have any questions or want to share some designs you are working with. To start playing, check out the latest TileMill build on Github.