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The magnitude 9.0 earthquake near Sumatra on December 26, 2004 was one of the most significant seismic events on Earth during the past 100 years. While earthquake damage and casualties were limited to the immediate vicinity of the earthquake, tsunamis generated by this event caused over 150,000 deaths in the Indian Ocean region spanning more than 10 nations.

This record section plot displays vertical displacements of the Earth's surface recorded by seismometers plotted with time (since the earthquake initiation) on the horizontal axis, and vertical displacements of the Earth on the vertical axis (note the 1 cm scale bar at the bottom for scale). The traces are arranged by distance from the epicenter in degrees. The earliest, lower amplitude, signal is that of the compressional (P) wave, which takes about 22 minutes to reach the other side of the planet (the antipode). The largest amplitude signals are seismic surface waves that reach the antipode after about 100 minutes. The surface waves can be clearly seen to reinforce near the antipode (with the closest seismic stations in Ecuador), and to subsequently circle the planet to return to the epicentral region after about 200 minutes. A major aftershock (magnitude 7.1) can be seen at the closest stations starting just after the 200 minute mark (note the relative size of this aftershock, which would be considered a major earthquake under ordinary circumstances, compared to the mainshock).

 

Credits: Data provided by the IRIS/USGS Global Seismographic Network, and distributed through the IRIS Data Management System. Seismic stations are operated by the US Geological Survey, Albuquerque Seismological Laboratory, and the University of California, San Diego. Support for these networks is provided by the National Science Foundation (through the IRIS Consortium) and U.S. Geological Survey.

Figure by Richard Aster, New Mexico Institute of Mining and Technology.