Columbia subject headings:
Earth (Planet)--Crust--Congresses.
Seismic reflection method--Congresses.
Seismic refraction method--Congresses.
Harvard subject headings:
Earth (Planet)--Crust--Congresses.
Seismic reflection method--Congresses.
Seismic refraction method--Congresses.
Princeton subject headings:
Earth--Crust--Congresses.
Seismic reflection method--Congresses.
Seismic refraction method--Congresses.