A seismologist says about three-fifths of an active fault running more than 50 kilometers off the northeastern prefecture of Fukushima shifted in last month’s powerful earthquake.
The magnitude-7.4 quake on November 22nd registered a 5 minus on the Japanese seismic scale of 0 to 7. A tsunami 1.4 meters high was observed at a port in Miyagi Prefecture.
Professor Shinji Toda of Tohoku University analyzed the active fault that triggered the temblor, using data on seabed terrain and the locations of aftershocks.
He says a stretch of about 30 kilometers in the fault that runs from northeast to southwest shifted in the earthquake.
He believes a shift of the entire fault would have caused a more powerful quake, with a possible magnitude of 7.7.
He warns that the remaining part of the fault is close to the shore and has the potential to trigger a magnitude-7 quake.
Toda’s findings contradict a 2014 analysis of the area by Tokyo Electric Power Company, the operator of the damaged Fukushima Daiichi nuclear power plant.
It stated that 2 fault lines, each about 20 kilometers long, could cause an earthquake with a magnitude of up to 7.1, much less than that of November’s quake.
Toda says it is important to improve that analysis, since the quake was more powerful than the utility’s estimate.
TEPCO says it will review its estimates if necessary.