November 28, 2012

Animations and Sonifications of the Tohoku earthquake and aftershocks

Posted by Austin Elliott

The M9.0 Tohoku earthquake that roared through Japan on March 11, 2011 made its presence felt in various ways throughout the planet. The ground rippled, the ocean churned, and even the atmosphere undulated with heavy pressure waves as the force of this sudden lurch of the Earth’s crust radiated outward from its source off the coast of Japan.

[Put your headphones on now.]

Scientists all over the world have taken data of all stripes and turned them into illustrative visualizations–like the examples listed above–of the extent of this seismic event. Most of these are old news, but for some reason I thought of them today, so here they are for your illumination.

One of the most captivating effects of this earthquake–and of any–is the aftershock sequence it unleashed. Aftershocks represent the relief of intense local stresses left by the abrupt perturbation of a mainshock, and they unfold in a statistically predictable manner (there’s a fun presentation by USGS scientist Karen Felzer explaining the remarkable features of aftershock sequences here). Despite this statistical order, in our relatively fast-paced human timescale, we may still perceive them as startling and chaotic, especially when we’re on edge in the aftermath of a major quake. Sped-up animations of earthquake occurrence (“seismicity”) help illustrate the decay in frequency and size of aftershocks with time, as well as simply illustrating just how numerous they may be after a large mainshock.

This video shows one year of earthquakes greater than magnitude 4.5 around the globe. Many mainshock-aftershock sequences are apparent, but by far the most spectacular is the series of quakes that is induced by the gargantuan Tohoku earthquake. Enjoy.

This same group has produced several other videos, either covering different time spans, or zooming in to Japan. Have a look at their website:

http://monoroch.net/jishin2011/

One of my favorite videos of this flavor is the “sonification” of seismic records from the day of the quake, like the one at the beginning of this post. Earthquakes shake the ground at frequencies lower than human hearing (infrasonic), but if we simply speed up the playback of seismic records, and translate their motions into oscillation of a speaker cone, we get the “sound” of the earthquakes. In that “sonification” video you see seismograms from four different stations in Japan and Russia that record the mainshock and the onslaught of aftershocks–including a 7.9–that follow. The inset map shows energetic yellow glows surrounding each station that are scaled to reflect the amplitude of the seismic waves recorded there.

If those aren’t enough coolness for you, there’s a whole page of different “sonifications” compiled by a Georgia Tech researcher illustrating different phenomena associated with the monster quake. Several of the clips play regional recordings of the mainshock and its aftershocks, but the compilation continues into recordings from the other side of the planet, where seismometers in California recorded the San Andreas Fault creaking and shuffling with triggered tremor as the long slow elastic waves from Tohoku swept through.

A seismic record section and frequency spectrogram show the first hour following the Tohoku quake. Click the image for the movie with audio. Quicktime format. The link to other videos and formats is below.

Earthquake Sound of the Mw9.0 Tohoku-Oki, Japan earthquake

If you’re into these sorts of things, there are more to be found… The California Integrated Seismic Network has some sped-up recordings of the 2004 M6.0 Parkfield earthquake and its aftershocks, at http://www.cisn.org/special/evt.04.09.28/sounds.html