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The ULF/ELF short‐term electromagnetic precursor is discovered for the disastrous Japan earthquake (EQ) occurred on 11 March 2011. This analysis is based on the records measured by search coil magnetometers located at Nakatsugawa (geographic coordinates; 35.42°N, 137.55°E), Shinojima (34.67°N, 137.01°E), and Izu (34.64°N, 137.01°E) of the Chubu University network. The data of these magnetometers are extensively used to analyze the ULF/ELF seismo‐atmospheric radiation. It is then found that the ULF/ELF atmospheric radio emission is reliably detected on 6 March before the main shock on 11 March, probably as a precursory signature of the EQ. Further confirmation on its seismic origin was provided by the observational fact that the azimuths of the radiation source from all observation sites coincide approximately with the region of the forthcoming EQ.

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A highly stressed area where eventual ruptures have often been observed to nucleate is characterized by low b values of earthquake frequency‐size distribution. Crustal deformation due to the occurrence of large earthquakes causes stress perturbation in nearby regions, so an investigation into spatiotemporal b values can play a crucial role in the distribution of postseismic hazards after the 2016 Kumamoto earthquake sequence along the Futagawa‐Hinagu fault zone, which culminated in the magnitude 7.3 mainshock. Together with an analysis of aftershock decay p value that can be used to infer stressing history, a highly stressed area with a characteristic dimension of 10 km at the southern end of the causative faults was found. Our observation is explained by postseismic deformation due to an afterslip on the causative faults and viscoelastic relaxation model. Similar to the Kumamoto mainshock rupture, which started at a low‐b‐value area, the observed highly stressed area shows a high likelihood of future earthquake ruptures.

By using network observation of subionospheric VLF (very low frequency)/LF (low frequency) signals in Japan and in Russia, we have found a significant ionospheric perturbation prior to the recent 2011 March 11 Japan earthquake (EQ) which occurred at sea proximate to the Tohoku area on the main island (Honshu) of Japan was an exceptionally huge plate-type EQ. A remarkable anomaly (with a decrease in the nighttime amplitude and also with enhancement in dispersion) was detected on March 5 and 6 along the propagation path from the NLK (Seattle, USA) transmitter to Chofu (together with Kochi and Kasugai). We also have observed the corresponding VLF anomaly during a prolonged period of March 1 -6, with minima in the nighttime amplitude on March 3 and 4 along the path from JJI (Miyazaki, Kyushu) to Kamchatka, Russia. This ionospheric perturbation has been discussed extensively with respect to its reliability. (1) How abnormal is this VLF/LF propagation anomaly? (2) What was the temporal evolution of terminator times? (3) Were there any solar-terrestrial effects (especially the effect from geomagnetic storms) on the VLF/LF propagation anomaly? (4) The effect of any other EQs and foreshock activities on the VLF/LF anomaly? (5) Were there any correlations with other related phenomena? Finally, (6) are there any other examples of a VLF/LF propagation anomaly for oceanic EQs? We then compared the temporal properties of ionospheric perturbations for this EQ with those of a huge number of inland EQs and compared the corresponding spatial scale with the former result of the same oceanic 2004 Sumatra EQ with nearly the same magnitude. Finally, the generation mechanism of those seismo-ionospheric perturbations is briefly discussed.