Animated Map Plots One Year of Quakes

BY Jenny Marder  February 13, 2012 at 10:50 AM EST

Updated: Feb. 14| We recently stumbled on this animated map that plots 2011′s biggest earthquakes.*

Each circle represents an earthquake — the bigger the circle, the greater the magnitude. The line across the circle indicates the quake’s depth. Most notable are the images that overwhelm the map on and just after March 11, when Japan’s magnitude-9.0 Tohoku earthquake and resulting aftershocks struck, unleashing a devastating tsunami that erased towns and caused a nuclear accident at the Fukushima Daiichi plant.

The data comes from the U.S. Geological Survey and the Japanese Meteorological Agency, and the video comes from the Japanese website, monoroch.net. While the circles and line graph running across the map show earthquakes that registered at magnitude 4.5 and up, the text scrolling across the bottom show magnitude 6 and greater quakes. A series of graphs at the end plot variations of both.

“I think the graphical representation is helpful, especially for giving a sense of how earthquakes are distributed, both around the globe and also how they’re distributed in time,” said Michael Blanpied, associate coordinator of the Earthquake Hazards Program at USGS. “You get these bursts of seismicity. The most obvious is Japan, where you see a raging torrent of aftershocks.”

While data from one year don’t represent a statistically significant sample size, the map appears to be plotted correctly, said Paul Caruso, a geophysicist with USGS.

“To me, this really illustrates that most of the earthquakes occur in the Pacific Ring of Fire,” he said.

The Pacific Ring of Fire contains the most violent seismic activity in the Pacific basin and includes Japan, the western coast of South and Central America, Alaska, Guam, Papua New Guinea and New Zealand.

“The Pacific plate is moving north,” Caruso added. “It’s being subducted under the Aleutian Islands and Alaska… and pushed under Japan. It’s moving, so that’s why we have earthquakes there. And of course the boundaries of that plate are some of the biggest faults in the world.”

Blanpied notes that the two line graphs have a similar shape even though they measure different magnitudes. “The relationship between small and large earthquakes holds when they’re frequent or when they’re infrequent,” he said. “If we happen to have a year with more large earthquakes, we’ll have more small ones as well, and vice versa.”

*After some questions about the video, we’ve updated the post to clarify which earthquakes are plotted in the animation and accompanying graphs.