The global positioning system (GPS) can be used to monitor the seismic perturbation induced by the 2011 off the Pacific coast of Tohoku Earthquake (magnitude 9.0), Japan, on March 11, 2011, and to trace the tsunami across the Pacific Ocean by measuring the changes in the ionospheric total electron content (TEC). We estimate the vertical and horizontal mean speeds of the seismic and tsunami waves using the time and distance of the TEC perturbation, and then, taking into account those determined speeds, trace back to the epicenter and the tsunami origin by applying a 3-dimensional spherical model. The results show that both the tracked epicenter and the tsunami origin are quite close to the epicenter reported by the USGS, with a mean horizontal propagation speed of 2.3 km/s after the earthquake and about 210 m/s after the tsunami. This consistency confirms that the perturbation sources in the ionosphere are due to the earthquake. This implies that the GPS-TEC measurements have the potential to be part of a lower cost, ground-based, tsunami monitoring system.
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