Add map layers

[shaefner-usgs]

Add additional layers:

• Moment tensor
• Focal mechanism
• ShakeMap stations
• Foreshocks
• Fieldnotes
• ShakeMap mmi, pga, pgv contours
• DYFI
• Seismic + geodetic stations by category (continuous GPS, campaign GPS, broadband
  seismic, strong­motion seismic, structural instrumentation)
• Surface geology

[shaefner-usgs]

Fieldnotes: #38

[baagaard-usgs]

I would be inclined to drop ShakeMap, DYFI, and seismic+geodetic stations from this list. The event pages contain an interactive map that can overlap ShakeMap, DYFI, and stations used in ShakeMap. IRIS has a JavaScript webpage for browsing station locations.

The surface geology would be nice. Oliver Boyd pointed me to https://ngmdb.usgs.gov/ngmdb/ngmdb_home.html.

[shaefner-usgs]

My thought was that these additional layers would be more useful in the context of the response app's map layers so they can all be viewed together on the same map. They can be off by default and fetched on demand (what I propose if we do include them) if you're concerned about download size. Or we can drop them if you don't think it's worth having them.

I checked out the URL you shared. I don't see any mention of an API/tile server for integrating these maps in a 3rd-party app. Poking around in the devtools a bit, it looks like maybe they're vector tiles coming from ArcGIS online, but I wasn't able to track them down. Are these available as a free service or as part of our ESRI license? It looks like Leaflet might support vector tiles with a plugin, but I don't have any experience using it.