LAUSR

The 2011 Tohoku-Oki earthquake, of moment magnitude (Mw) 9.0, occurred on March 11, 2011, on the boundary between the Pacific and North America tectonic plates. 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. I used data from nine borehole strainmeters deployed by the National Institute of Advanced Industrial Science and Technology to estimate a fault model with Mw of 8.7 for the 2011 earthquake. 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). 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. 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.