North Korea nuclear test seismogram - crustal phases

Figure from the Nevada Seismological Laboratory

Back on January 17, I had an entry on crustal phases. We should do a short review to understand the nomenclature shown in the diagram in the last blog for the seismic phases seen on China seismograms after the Korea nuclear test.

You can find a listing of seismic phases here.

Note in particular the phases shown in the previous quake observed for the NK nuclear test:

• Pg - at short distances, an upgoing P wave from a source in the upper crust; otherwise, a wave refracted from a mid-crustal discontinuity
  
• Pn - a P wave refracted along the crust-mantle boundary
  
• Sg - at short distances, an upgoing S wave from a source in the upper crust
  
• Sn - an S wave refracted along the crust-mantle boundary

Rayleigh and L waves are surface waves.