Anomalous effect in Schumann resonance phenomena observed in Japan, possibly associated with the Chi-chi earthquake in Taiwan

Abstract

Abstract. The Schumann resonance phenomenon has been monitored at Nakatsugawa (near Nagoya) in Japan since the beginning of 1999, and due to the occurance of a severe earthquake (so-called Chi-chi earthquake) on 21 September 1999 in Taiwan we have examined our Schumann resonance data at Nakatsugawa during the entire year of 1999. We have found a very anomalous effect in the Schumann resonance, possibly associated with two large land earthquakes (one is the Chi-chi earthquake and another one on 2 November 1999 (Chia-yi earthquake) with a magnitude again greater than 6.0). Conspicuous effects are observed for the larger Chi-chi earthquake, so that we summarize the characteristics for this event. The anomaly is characterized mainly by the unusual increase in amplitude of the fourth Schumann resonance mode and a significant frequency shift of its peak frequency (∼1.0 Hz) from the conventional value on the B y magnetic field component which is sensitive to the waves propagating in the NS meridian plane. Anomalous Schumann resonance signals appeared from about one week to a few days before the main shock. Secondly, the goniometric estimation of the arrival angle of the anomalous signal is found to coincide with the Taiwan azimuth (the unresolved dual direction indicates toward South America). Also, the pulsed signals, such as the Q-bursts, were simultaneously observed with the "carrier" frequency around the peak frequency of the fourth Schumann resonance mode. The anomaly for the second event for the Chia-yi earthquake on 2 November had much in common. But, most likely due to a small magnitude, the anomaly appears one day before and lasts until one day after the main shock, with the enhancement at the fourth Schumann resonance mode being smaller in amplitude than the case of the Chi-chi earthquake. Yet, the other characteristics, including the goniometric direction finding result, frequency shift, etc., are nearly the same. Although the emphasis of the present study is made on experimental aspects, a possible generation mechanism for this anomalyCorrespondence to: M. Hayakawa (hayakawa@whistler.ee.uec.ac.jp) is discussed in terms of the ELF radio wave scattered by a conducting disturbance, which is likely to take place in the middle atmosphere over Taiwan. Model computations show that the South American thunderstorms (Amazon basin) play the leading role in maintaining radio signals, leading to the anomaly in the Schumann resonance.

Localized ionospheric disturbance over the earthquake epicentre and modifications of Schumann resonance electromagnetic fields

“…The South American thunderstorms provide the most distinct modifications in the SR spectra for the EQs at Taiwan and the observer positioned in Japan. This follows from the specific geometry of radio propagation when all three points tend to lie approximately at the same great circle, and the details might be found in the papers by Hayakawa et al (2005aHayakawa et al ( , 2010b, Nickolaenko et al (2006b), and Ohta et al (2001Ohta et al ( , 2006. We show the model data for the simple point source because these reveal characteristic discontinuities in the power spectra arising from the frequency changes of modulation factor B z .…”

“…Hayakawa et al 2005b;Nickolaenko & Hayakawa 2002;Nickolaenko et al 2006aNickolaenko et al , 2006bPechony et al 2006). We will use the data set applied in the papers by Hayakawa et al (2005aHayakawa et al ( , 2010b, Nickolaenko et al (2006a), and Ohta et al (2001Ohta et al ( , 2006. The model contains the 24 maps of spatial distribution of lightning strokes over the globe.…”

“…This means that we suggested that random strokes form a Poisson pulsed succession, so that their "intensities are summed". Finally, the complete power spectra were computed in the regular and disturbed cavities by integrating the "observed" contributions from all cells of the global map (Ohta et al 2001(Ohta et al , 2006Hayakawa et al 2005aHayakawa et al , 2010bNickolaenko et al 2006aNickolaenko et al , 2006b). …”

“…Anomalous radio signals in the Schumann resonance (SR) band were reported for the first time in a series of works (Ohta et al 2001(Ohta et al , 2006Hayakawa et al 2005aHayakawa et al , 2008Hayakawa et al , 2010b. Analyses of the long-term SR records indicated that anomalies are usually observed in Japan when earthquakes (EQs) occur in Taiwan.…”

“…We concentrate in the present study on the first kind of model interpretation and address modulations in all electromagnetic field components: the vertical electric E z and two orthogonal magnetic field components H WE and H SN because we have considered only the vertical electric field in our previous papers (e.g. Hayakawa et al 2005a).…”