What Does It Feel Like to be On Top of a Nuclear Test?

Since North Korea claimed to have tested a nuclear weapon on Monday, geologists and policy wonks have been wondering why the tremor the detonation caused was so small. Was the bomb small, not very good, or fake -- simply a pile of regular explosives? While the authorities study and debate, I am struck by the surrealness of the situation. Human beings have weapons that imitate tectonic plate movements!

I grew up in southern California and have been through several earthquakes, including the magnitude 6.6 Northridge Earthquake in 1994. When I read about the North Korean nuclear-seismological debate, I wondered what it would feel like to be on top of an underground nuclear test.

To find out, I combined a Wikipedia chart of the Richter scale magnitudes of various earthquakes and explosions with a chart giving rough conversions between earthquake magnitudes on the Richter scale and their felt intensities on the Modified Mercali Scale. Here is the result.

Event	Richter magnitude	TNT Equivalent	Intensity
WWII conventional bombs	1.5	178 kg (392 lb)	Detected only by seismographs
late WWII conventional bombs	2.0	1 metric ton	Detected only by seismographs
WWII blockbuster bomb	2.5	5.6 metric tons	Detected only by seismographs
Small atomic bomb	4.0	1 kiloton	Resembling vibrations caused by heavy traffic.
Nagasaki atomic bomb	5.0	32 kiloton	Sleepers awakened and bells ring.
Little Skull Mtn, NV Quake, 1992	5.5	178 kilotons	Trees sway, some damage from overturning and falling objects.
Double Spring Flat, NV Quake, 1994	6.0	1 megaton	General alarm, cracking of walls.
Northridge quake, 1994	6.5	5.6 megatons	Chimneys fall and there is some damage to buildings.
Tsar Bomba, largest thermonuclear weapon ever tested	~7.0	50 megatons	Ground badly cracked and many buildings are destroyed. There are some landslides.
Landers, CA Quake, 1992	7.5	178 megatons	Ground badly cracked and many buildings are destroyed. There are some landslides.