NOTE: The reported increase from 8.9 to 9.1 on the Richter scale would not be an incremental rise, but approximately a doubling in magnitude. Richter uses a base-10 logarithmic scale- read more here.
8.9 - 336 megatons 1.41 EJ Japan earthquake, 2011 (1st reported number)
9.0 - 474 megatons 2.00 EJ Lisbon Earthquake (Portugal), All Saints Day, 1755
9.1 —- [roughly 600-700 megatons] newly-reported number for Japan earthquake, 2011]
9.2 - 946 megatons 3.98 EJ Anchorage earthquake (Alaska, USA), 1964
March 12, 2011
The Japan earthquake was the fourth most powerful ever recorded with a magnitude of 9.1, twice more powerful than the initial estimate of 8.9, Gerard Fryer, geophysicist of the Pacific Tsunami Warning Center, said this morning.
Three others that were more powerful since the late 1800s when seismometers started measuring ground motions were in 9.5 in Chile in 1960, 9.2 in Alaska in 1964 and 9.1 in Sumatra in 2004, according to Fryer.
The new magnitude was adjusted based on the impact of the quake throughout the Pacific, he said. “It fits all measurements, including in Hawaii,” Fryer said.
The U.S. Geological Survey estimate of the quake’s magnitude is still 8.9.