https://www.mtu.edu/geo/community/seismology/learn/earthquake-epicenter/
https://www.mtu.edu/geo/community/seismology/learn/seismology-study/
http://eqseis.geosc.psu.edu/cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html
https://manoa.hawaii.edu/exploringourfluidearth/physical/ocean-floor/layers-earth/compare-contrast-connect-seismic-waves-and-determining-earth-s-structure