Tsunami Quake Shakes up the Earth

The Sumatra-Andaman earthquake, which triggered the Indian Ocean tsunami on December 26, 2004, was the largest earthquake ever recorded using the modern digital instruments that were developed within the last thirty years. It spread further, lasted longer, and triggered the most distant and intense secondary quakes ever recorded.

The December 26 earthquake, which had a magnitude of 9.15, moved every spot on the Earth’s surface by at least a centimeter. The seismic wave was imperceptible in most places, though, because it moved so slowly. Unlike most earthquakes, which only last for a few seconds, this quake lasted almost 10 minutes. It shook the ground at least 100 more times than the 1994 Los Angeles earthquake.

The Sumatra-Andaman quake triggered the most distant small earthquakes ever detected. The Mount Wrangell volcanic area in Alaska, 11,000 kilometers away, was shaken by 14 tiny earthquakes in 11 minutes. These were in synch with the pulses of the Sumatra-Andaman quake.

According to Jeffery Park of Yale University, a distinctive vibration frequency left over from the earthquake was still detectable in mid-May 2005, moving the ground about half a micrometer, and should remain detectable for a couple more months.