The Mainichi has a very interesting article on North Korea's probable nuclear explosion. The article explains how Japanese scientists used the explosion's waveform to distinguish it from a naturally occurring earthquake:
Natural earthquake vs. nuclear test: waveform graphs tell the story. The Mainichi, January 6, 2016 (Mainichi Japan) http://mainichi.jp/english/articles/20160106/p2a/00m/0na/011000c
North Korea claimed on Jan. 6 that it had tested a hydrogen bomb. Before the official announcement, however, news agencies were already reporting a possible nuclear test after an "artificial" earthquake was detected with its epicenter around North Korea's nuclear testing site in the northeast of the country...
How can earthquake monitoring agencies tell the difference between a natural quake and one caused by a nuclear blast? The answer is in the incident's waveform. The undulations in the ground produced by a natural quake build to a sudden crescendo, while those produced by an underground nuclear test spike at the very beginning and then trail off....I recommend reading the original article because it includes sample waveforms.
Just out of curiosity I searched for a seismograph of the 3/11 earthquake in Japan, the Great Honshu quake of 2011.
Here are a couple of findings:
VUME Virtual Upper Mantle of the Earth http://www.virtualuppermantle.info/2011-Sendai-Japan.htm
Sonification of Tohoku Earthquake https://www.youtube.com/watch?v=3PJxUPvz9Oo
I particularly recommend the second link, sonification of Tohoku Earthquake.