Earthquakes of this size outside of subduction zone are very rare. In contrast, the Great Tohoku earthquake had no aftershock above M7.Īll but one of the 15 M8+ earthquakes since 2000 are on the edges of oceanic plates, and are located in subduction zones. Seeing that kind of activity, people may almost be happy to live in Alaska instead. The Sumatra quake is particularly interesting since there are 5 M8+ events close together on the map: the M9.1, an M8.6 aftershock very close to it which happened a year later, a double M8.2/M8.6 8 years later, which were on the oceanic side of the subduction fault and presumably due to faults there which were stressed by the 2004 event, and finally an M8.7 much further along Sumatra in 2007 which may be due to stress transfer at the edge of the rupture zone of 2004. They include the Great Tohoku earthquake and the 2004 Sumatra earthquake. 10 of these were along the Pacific, and the remainder cluster along Indonesia in the Indian ocean. Since 2000, there have been 15 earthquakes of M8.2 or larger on Earth. The nice looking one is the S wave, arriving 10 minutes later but remaining visible for several hours.Įarthquakes this size occur somewhere on Earth on average once every one or two years. The irregular part at the start (red) is the P-wave. This is the faf low-frequency seismograph plot, which should be showing the eruption but instead shows the Alaskan waves passing. The Alaska earthquake and the Iceland volcano.
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