Jeffrey Park

Articles by Jeffrey Park

26 February 2013

A broader reading of seismic waves from North Korea

Jeffrey Park

A few minutes short of noon, local time, on February 12, an underground blast in a remote corner of North Korea sent seismic waves worldwide, leaving clear recordings on thousands of seismometers. Some of these seismological recorders belong to clandestine intelligence-gathering networks in the service of individual nations. You and I will probably never see the data gathered by these networks, but we don't need to. Primarily to monitor earthquakes within active fault zones, thousands of seismometers around the globe record ground motion and distribute that information to the public.

16 March 2011

Earthquake 9.0: What this magnitude might mean for Japan's future

Jeffrey Park

When the magnitude of the earthquake off Tohoku, Japan, was calculated to be 9.0, it joined the ranks of "megathrust" earthquakes -- exceptionally large ruptures involving 5 to 10 meters of slip motion on fault zones more than 100 kilometers in length. These massive earthquakes occur along Earth's subduction zones, that is, where two 150-kilometer thick plates of solid rock collide.

26 May 2009

The North Korean nuclear test: What the seismic data says

Jeffrey Park

According to early reports, Monday's North Korea event certainly seems like a deliberate explosion in the right place. However, it was too small to be a successful Hiroshima-class crude explosive device, by a factor of three or four. The reported estimates of Richter magnitude spread from 4.5-5, and the standard conversions to explosive yield suggest a yield of 2-6 kiloton-equivalents of TNT. Most of the latest Richter magnitude estimates have come in the low half of the 4.5-5 range, so it seems likely that the yield was 4 kilotons or smaller.