USGS follows the GeoJSON spec for geographic features. So if you’ve worked with this spec int he past it should be a qauick read.
USGS doucments the params you can pass here: http://earthquake.usgs.gov/fdsnws/event/1/
Earthquakes for the last 24 hours: http://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_day.geojson
You can get more detail on an event by passing an id: http://earthquake.usgs.gov/fdsnws/event/1/query?eventid=hv60995496&format=geojson
From there you can get a list of cities close to the event: http://earthquake.usgs.gov/archive/product/nearby-cities/hv60995496/us/1438426393480/nearby-cities.json
Its a fun API. The best I’ve worked with in a while. Would really like to see USGS pass it on to GeoMAC Wildfire feed.