One such approach is based on geodetic rather than seismic data. ![]() Because the discrepancy between the preliminary JMA magnitude and the final moment magnitudes was large, researchers have sought alternative methods for rapid magnitude determinations of great earthquakes. However, for very large earthquakes, seismic records can be saturated, which compromises the use of maximum amplitudes to determine earthquake magnitudes. M JMA is a magnitude scale based on the maximum amplitude observed on seismograms. Immediately after shaking commenced, the Japan Meteorological Agency (JMA) issued a preliminary report for the event that included a preliminary magnitude ( M JMA) of only 7.9. Soon afterward, a giant tsunami struck the Pacific coast of eastern Japan and caused severe damage. The Tohoku-Oki earthquake, of moment magnitude M w 9.0, occurred at 14:46 Japan standard time on March 11, 2011. My results indicate that strainmeter data can measure large changes of static strain that can be used to rapidly and precisely estimate earthquake fault models and moment magnitudes for great earthquakes and can provide an important and useful complement to analyses based on seismic waves. To date, strainmeter data have rarely been used to derive earthquake fault models because observed strainmeter data often include noise caused by the local effect of earthquake shaking. ![]() ![]() This model was estimated using data recorded during the first 7 min after the origin time of the earthquake (5 min after the first P-wave arrival). I used data from nine borehole strainmeters deployed by the National Institute of Advanced Industrial Science and Technology to estimate a fault model with M w of 8.7 for the 2011 earthquake. The preliminary report of the magnitude announced by the Japan Meteorological Agency just after the earthquake was 7.9, which was considerably smaller than the final calculated Mw of 9.0. The 2011 Tohoku-Oki earthquake, of moment magnitude ( M w) 9.0, occurred on March 11, 2011, on the boundary between the Pacific and North America tectonic plates.
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