Abstract. Two different analysis methods; (1) mono-fractal analysis (based on Higuchi method) and (2) flicker noise spectroscopy, have been applied to the same ULF (frequency less than 10 Hz) electromagnetic data observed at Guam during 3 years including the 1993 August Guam earthquake. The results by these two methods are found to be very consistent with each other; that is, some precursory effects seem to start about 3 months before the earthquake. This gives us a strong support to the self-organizing critical process before the Guam earthquake.
Abstract. The VHF electromagnetic noise intensity data at several stations in the Tohoku area of Japan during the period of a rather large (with magnitude of 7.2) earthquake (Miyagi-ken oki earthquake) taken place on 16 August 2005, are analyzed by means of different fractal analysis methods, including (1) spectral slope estimation, (2) multi-fractal detrended fluctuation analysis and (3) multi-fractal wavelet transform modulus maxima method. It seems to the authors that there is no definite analysis method for the analysis of any seismogenic phenomenon, so that the only way we have to take, is to apply different methods to the same data for the detailed comparison of the results. This comparison enables us to deduce the properties commonly observed by the above methods. Because the most important feature common to these three methods, is that significant changes in fractal scaling characteristics are observed just during the earthquake (mainly before the earthquake) only at one station of Kunimi. Finally, we can come to the definite conclusion on the self-organization of VHF emissions only at one station in the present case.
Abstract. The data on radio telemetry links (for water information) at VHF/UHF in Hokkaido are used to investigate the rate of disturbances on radio links (or connection failure) and its association with a huge earthquake, Tokachi-oki earthquake on 26 September 2003. Especially, the telemetry links at the Tokachi region closest to the earthquake epicenter, showed a significant increase in disturbances on radio links two weeks to a few days before the earthquake on the basis of analysis during a long interval from 1 June 2002 to 3 November 2007 (over 5 years). We suggest that these severe disturbances in VHF/UHF telemetry links are attributed to the generation of seismogenic VHF/UHF radio noises (emissions). Based on this idea, we have estimated that the intensity of these seismogenic emissions is on the order of 10–19 dB μV/m. Finally, the present result was compared with other physical parameters already obtained for this earthquake.
Abstract. An improved analysis of polarization (as the ratio of vertical magnetic field component to the horizontal one) has been developed, and applied to the approximately four years data (from 1 March 2003 to 31 December 2006) observed at Kashi station in China. It is concluded that the polarization ratio has exhibited an apparent increase only just before the earthquake on 1 September 2003 (magnitude = 6.1 and epicentral distance of 116 km).
Abstract. Fractal analysis has been applied to the local nighttime data of subionospheric LF propagation, and the fractal dimension is estimated every day in the two distinct frequency ranges (AW: acoustic wave and AGW: atmospheric gravity wave). The data during several years are analyzed for the propagation paths from the Japanese transmitter of JJY to Moshiri (Hokkaido) and to Kochi. As the result of analysis, we come to the conclusion that when we pay attention to the period just around the earthquake, we sometimes detect some significant increases in the fractal dimension either in AW or AGW range. This indicates that the self – organization effect prior to an earthquake in the lithosphere, might be seen even in the lower ionosphere, probably in terms of atmospheric oscillation effect.
Abstract. The ELF observation at Moshiri (geographic coordinates: 44.29° N, 142.21° E) in Hokkaido, Japan, was used to find anomalous phenomena in the Schumann resonance band, possibly associated with a large earthquake (magnitude of 7.8) in Taiwan on 26 December 2006. The Schumann resonance signal (fundamental (n=1), 8 Hz; 2nd harmonic, 14 Hz, 3rd harmonic, 20 Hz, 4th, 26 Hz etc.) is known to be supported by electromagnetic radiation from the global thunderstorms, and the anomaly in this paper is characterized by an increase in intensity at frequencies from the third to fourth Schumann resonance modes mainly in the BEW component with a minor corresponding increase in the BNS component also. Spectral modification takes place only in the interval of 21:00 UT±1 h, which corresponds to the global lightning activity concentrated in America. While distortions were absent in other lightning-active UT intervals, in particular, around 08:00 UT±1 h (Asian thunderstorms) and around 15±1 h (African lightning activity). The anomaly occurred on 23 December three days prior to the main shock. The results observed were explained in terms of ELF radio wave perturbation caused by the lower ionospheric depression around the earthquake epicenter. The difference in the path lengths between the direct radio wave from an active global thunderstorm center and the wave scattered from the non-uniformity above Taiwan causes interference at higher resonance modes, which is successful in explaining the observational data.
