No. 385: Figuring out the magnitude of a big earthquake in one hundredth of a second (December 20, 2011)

Railway Technical Research Institute developed a technology to figure out the magnitude of a big earthquake instantly. The institute focused on how long it takes the quake grows strongest after the arrival of the S wave that is the second wave of an earthquake. The technology figures out the time using the data of past earthquakes higher than 5.0 in magnitude accumulated by National Research Institute for Earth Science andDisaster Prevention. The existing technology needs two days to figure out the magnitude of such a big earthquake as the East Japan Great Earthquake that is about 9.0 in magnitude, but the new technology can figure out the magnitude in one hundredth of a second. The institute plans to put this new technology into practical use in half a year as a correction technology.

The study on the time between the arrival of the S wave and the maximization of the quake revealed that the bigger an earthquake is, the longer the time between the two points is. For example, the time is 7-8 seconds in the case of an earthquake of magnitude of 7.0, but it is 30-40 seconds if an earthquake is 8.0 in magnitude. If an earthquake is 9.0 in magnitude, the time grows to be about 100 seconds. The new technology calculates back the magnitude of an earthquake using the time between the two points. The method currently used by Japan Meteorological Agency tends to underestimate an earthquake higher than 8.0 in magnitude. In fact, Japan Meteorological Agency claimed that the East Japan Great Earthquake was 7.9 in magnitude on the day, but it corrected its magnitude as 9.0 two days later.