This plot shows earthquakes near Japan: the horizontal axis is time, the vertical axis is distance from the Fukushima Daiichi nuclear power plant. Different sizes/colors of points indicate different sized earthquakes from magnitude 4.5 to the main 9.0 earthquake of 11 March 2011 (time of this quake indicated by the vertical black line).
This shows the large number and geographic range of aftershocks following the main shock on 11 March. Five of these aftershocks were magnitude 6.5 to 7.2, similar in strength to the Loma Prieta and Northridge earthquakes in California in 1989 and 1994, respectively. One aftershock, 29 minutes later, was magnitude 7.9, similar in strength to the 1906 San Francisco earthquake.
This plot shows the location near Japan of the earthquakes in the above graph. Most of these earthquakes are off the eastern coast of the main Japanese island of Honshu. This region represents part of the area of subduction of the Pacific plate under Japan: the Tohoku earthquake is associated with where the Pacific plate of the Earth's crust slides underneath the plate of the Earth's crust that Japan is on. The contact between the plates is the Japan trench, and from there the Pacific plate drops into the Earth's mantle. The average westward motion of the Pacific plate relative to Japan is about 6 cm/year.
Largest earthquakes since 1900 (USGS data)
|31 JAN 1906||Pacific Ocean, off Ecuador coast||8.8||1.00 N||81.50 W|
|11 NOV 1922||Chile-Argentina border||8.5||28.55 S||70.50 W|
|3 FEB 1923||Kamchatka, Russia, USSR||8.5||54.00 N||161.00 E|
|1 FEB 1938||Banda Sea, off Indonesia||8.5||5.05 S||131.62 E|
|15 AUG 1950||Assam-Tibet||8.6||28.50 N||96.50 E|
|4 NOV 1952||Kamchatka, Russia, USSR||9.0||52.76 N||160.06 E|
|9 MAR 1957||Andreanof Islands, Alaska, USA||8.6||51.56 N||175.39 W|
|22 MAY 1960||Chile||9.5||38.29 S||73.05 W|
|13 OCT 1963||Kuril Islands, Russia, USSR||8.5||44.90 N||149.60 E|
|28 MAR 1964||Prince William Sound, Alaska, USA||9.2||61.02 N||147.65 W|
|4 FEB 1965||Rat Islands, Alaska, USA||8.7||51.21 N||178.50 E|
|26 DEC 2004||Indian Ocean, off Sumatra, Indonesia||9.1||3.30 N||95.78 E|
|28 MAR 2005||northern Sumatra, Indonesia||8.6||2.08 N||97.01 E|
|12 SEP 2007||southern Sumatra, Indonesia||8.5||4.44 S||101.37 E|
|27 FEB 2010||Pacific Ocean, off Maule, Chile||8.8||35.85 S||72.72 W|
|11 MAR 2011||Pacific Ocean, off Tohoku, Honshu, Japan||9.0||38.32 N||142.37 E|
This table lists the largest earthquakes by magnitude since 1900: 16 quakes from magnitude 8.5 up to 9.5. The Tohoku earthquake is fourth largest. Of these 16 earthquakes, 4 occurred from 1906-1938, 7 from 1950-1964, and 5 from 2004-2011.
The information above is from the USGS page below on the largest earthquakes since 1900. Note that earthquake magnitudes are sometimes a matter of debate, particularly for historic earthquakes, for reasons including: different definitions of magnitude; lack of available measurements (for older earthquakes); and the fact that measurements for these largest earthquakes are difficult due to both large ground motion and large extent in area.
© 2011 by Wm. Robert Johnston.
Last modified 16 March 2011.
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