Won-Young Kim at the Lamont–Doherty Earth Observatory explained it "was more powerful than North Korea's previous nuclear test" and added that it is difficult to quantify "the exact size of North Korea's nuclear detonations because the depth of the explosive device, properties of the rock surrounding the explosion and other factors influence the seismic measurements produced" because North Korea does not publicize the depth of its tests, although the material at the Punggye-ri Nuclear Test Site is thought to be hard granite.
