At each K-NET and KiK-net station in Fig. 2, we took the average of log(B obs. /B theo. ) over all analyzed earthquakes detectable at the station, changing a to 150, 200, 600, and 1000 m.
A lower detectable limit of earthquake events using our strong motion array was estimated to be at least M > 4 for the whole focal region of the mainshock from the magnitude frequency diagram (Fig. 4c).
We demonstrate by both synthetic tests and real-data case studies that the coseismic gravitational changes due to the 2011 Tohoku-Oki earthquake are detectable by GRACE with only 1-month data after the earthquake.
We demonstrate that the coseismic gravitational changes due to the 2011 M w = 9.0 Tohoku-Oki earthquake are detectable by GRACE with only 1-month data after the earthquake, which is also supported by a simulation test using the seismic-signal-contained observations synthesized with the signals of a dislocation model prediction.
This result indicates that the piezomagnetic field may be a plausible mechanism of generating co-seismic changes in the magnetic field with detectable amplitudes for large earthquakes, provided that the observation site is located near the magnetization boundaries.
"These forces are the source of glacial earthquakes, globally detectable seismic events whose proper interpretation will allow remote sensing of calving processes occurring at increasing numbers of outlet glaciers in Greenland and Antarctica," the scientists wrote in the paper.
Rather than replacing seismic data, this method of analysis can accelerate detection and improve confidence that a "felt" earthquake (one detectable to humans) has definitely occurred, the paper explains.
Thus, this deep earthquake with a magnitude equivalent to that of a shallow magnitude 5 earthquake was able to generate detectable infrasound, but ground motions of the other, smaller deep earthquakes were not sufficient to generate detectable infrasound.
When a large earthquake occurs, an associated deformation disturbance called a seismic wave propagates through the adjacent rock, and the entire Earth is set into vibrations which, following a sufficiently large earthquake, may remain detectable with precise instruments for several weeks.
