In light of inaccurate data released after the Great East Japan Earthquake, Japan will begin an experiment from late March using the global positioning system to better estimate earthquake magnitudes and improve disaster management.
In light of inaccurate data released after the Great East Japan Earthquake, Japan will begin an experiment from late March using the global positioning system to better estimate earthquake magnitudes and improve disaster management.
Researchers hope the new system will allow for quicker estimations of the magnitudes of huge earthquakes as well as the height of any subsequent tsunami.
After the Geospatial Information Authority confirms the accuracy of the system, data will be provided to the Meteorological Agency.
The new procedure was developed in conjunction with Tohoku University and the University of Tokyo. The system uses crustal movement data that is updated every second at the 1,200 or so GPS control stations around Japan.
"We recognize the need to improve the speed and accuracy for determining quake magnitude and the focal area,” an official with the Meteorological Agency said. “If the data from the Geospatial Information Authority can be utilized, we plan to aggressively do so."
Under the GPS system, the extent and direction of crustal movements during an earthquake are used to calculate the extent of movement between plate borders of the faults where the quake occurred.
Those calculations will be used to estimate the magnitude of the quake.
The method is considered suitable for quickly estimating the magnitudes of huge earthquakes that involve major crustal movements.
The method was used to evaluate crustal movements when the magnitude-9.0 Great East Japan Earthquake struck off the Tohoku coast on March 11, 2011. The system showed that figures from 527 GPS control stations could be used to estimate a magnitude of 8.7 three minutes and 10 seconds after the quake hit.
However, the Meteorological Agency estimated the magnitude at 7.9 three minutes after the quake hit and issued a warning for a major tsunami.
About 75 minutes after the quake, the Meteorological Agency revised the magnitude to 8.4 and further revised it to 8.8 about two hours and 45 minutes after the quake.
Using different calculation methods, the U.S. Geological Survey announced a magnitude of 8.9 34 minutes after the quake struck.
The Meteorological Agency estimates quake magnitudes using seismic waves observed at seismographs.
However, when enormous quakes hit, the seismographs are unable to make measurements beyond a certain point.
Such problems do not arise when making estimates from crustal movement.
Moreover, because the movements on the ocean floor can also be calculated, the new system is expected to supplement the Meteorological Agency's system for estimating the scale of tsunami.
The Geospatial Information Authority will use the new system to estimate quakes with a magnitude of at least 7. If a huge quake should strike during the experiment, the crustal movement data will be provided to the Meteorological Agency.
After further improving the system and confirming the accuracy of the system by using data from past major quakes, a judgment will be made in the new fiscal year on whether the data could be used for disaster management purposes.
Experts said using various sources of data was important for estimating magnitudes.
"One lesson from the Great East Japan Earthquake for clarifying the scale of a quake and helping in future disaster management is to not depend on just a single source of data,” said Katsuyuki Abe, a professor emeritus at the University of Tokyo who chairs a Meteorological Agency committee looking into tsunami warnings. “It will be important to determine the magnitude by using a wide variety of data, and everything that can be used should be used."