you can paste those urls into the JSON data URL input on this page:
to get a more humanly-readable format.
for the earthquake.usgs.gov, scroll down 'til you see "geometry" - that's where the coordinates are stored
in the geonames ones they are stored at the first level, in the "lat" and "lng" keys
but there is a difference in the results that will make your implementation vary from google's - note that the usgs results come wrapped in a callback function - eqfeed_callback, whereas the geonames ones get served up as raw JSON. This means that you can call the callback after appending the usgs script and once the results are ready you can access that data.
But if geonames doesn't wrap their results in a callback (which I'm sure they do, you just have to find the parameter on their webpage) you would have to find some other way of accessing that info, maybe with a cross-domain ajax request (which will be annoying... I strongly recommend looking for a callback parameter first)
the second part of your problem will require you to geocode the address supplied:
then get the surrounding points (because the urls seem accept a box for the cardinal points - the bounds property of the geocode result will be useful for this:
and add them to the url before requesting it from geonames (or wherever)