Hundreds of large temblors were found to have struck in the sea off the eastern coast of the Tohoku region in the day after the Great East Japan Earthquake and went unrecorded by the Japan Meteorological Agency, a team of researchers found.
Researchers led by Miaki Ishii, a seismologist and associate professor at Harvard University, found that intense temblors of magnitude-5.0 or larger struck more than 430 times in 25 hours after the magnitude-9.0 earthquake hit, suggesting the severity of the aftershocks.
The JMA failed to detect and record those temblors following the massive March 11, 2011, quake.
The Harvard researchers cited the almost simultaneous occurrence of those aftershocks as a possible reason for the JMA's failure to detect them. They also said it might be related to the directions of the seismic waves and locations of the seismometers.
Using a special technique, Ishii’s team analyzed data obtained from seismometer networks in the United States in order to determine the locations where seismic energy was emitted.
For their difficulty to detect, the researchers named these undetected temblors the “stealth earthquakes” after fighter jets using stealth technology to avoid detection by radar.
Ishii’s team said it will continue to study to solve the mystery of stealth earthquakes.
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