Despite its extreme importance and years of effort, practical short-term earthquake prediction still remains to be seen. However, research in earthquake-related electromagnetic phenomena have recently shown that such phenomena make for a promising candidate for short-term earthquake prediction. There is a good deal of accumulated evidence of precursory signatures in a wide frequency range (DC-VHF). ULF geomagnetic change is one of the most promising phenomena and it suggests that short-term prediction is realizable. This report first reviews earlier observational facts and presents the latest results in detection of ULF emissions by means of sophisticated signal processing. Finally, we discuss the possible generation and propagation mechanism of earthquake-related ULF signals.

/pdf/ulf-geomagnetic-changes-associated-with-large-earthquakes-3ld4l0pbt7.pdf

ULF Geomagnetic Changes Associated with Large Earthquakes

Schumann Resonance for Tyros

In order to extract any ULF signature associated with earthquakes, the singular spectral analysis (SSA) and the principal component analysis (PCA) have been performed to investigate a possibility of discrimination of signals from different sources (geomagnetic variation, artificial noise, and the other sources (earthquake-related ULF emissions)). We apply SSA to the time series data observed at closely spaced stations; Seikoshi (SKS), Mochikoshi (MCK), and Kamo (KAM) stations. Then, PCA is applied to the time series data sets filtered at 0.01 Hz of NS component at three stations. In order to remove the most intense signal like the first principal component, we make the differential data sets of SKS–MCK and MCK–KAM for the above data. The major findings are summarized as follows. (1) It is important to apply simultaneously SSA and PCA, because SSA gives the structure of signals and the number of sensors for PCA is estimated. This makes the results more convincing. (2) There is a significant advantage using PCA with differential data sets of filtered (0.01 Hz band) signal between SKS–KAM and MCK–KAM in NS component for removing the most intense signal like global variation (solar–terrestrial interaction). This yields that the anomalous changes in the second principal component were detected more clearly, and the contribution of the second principal component is found to be 20–40%. It is enough to prove mathematical accuracy of the signal. Further application is required to accumulate events. These facts demonstrate a possibility of monitoring the crustal activity with using the SSA and PCA.

Singular spectral analysis and principal component analysis for signal discrimination of ULF geomagnetic data associated with 2000 Izu Island Earthquake Swarm

A correlation is investigated between the intensity of the global electromagnetic oscillations (Schumann resonance) with the planetary surface temperature. The electromagnetic signal was monitored at Moshiri (Japan), and temperature data were taken from surface meteorological observations. The series covers the period from November 1998 to May 2002. The Schumann resonance intensity is found to vary coherently with the global ground temperature in the latitude interval from 45° S to 45° N: the relevant cross-correlation coefficient reaches the value of 0.9. It slightly increases when the high-latitude temperature is incorporated. Correspondence among the data decreases when we reduce the latitude interval, which indicates the important role of the middle-latitude lightning in the Schumann resonance oscillations. We apply the principal component (or singular spectral) analysis to the electromagnetic and temperature records to extract annual, semiannual, and interannual variations. The principal component analysis (PCA) clarifies the links between electromagnetic records and meteorological data.

/pdf/evidence-on-a-link-between-the-intensity-of-schumann-o6rxe2q4h8.pdf

Evidence on a link between the intensity of Schumann resonance and global surface temperature

. 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.

/pdf/anomalous-elf-phenomena-in-the-schumann-resonance-band-as-2bqxq3s21a.pdf

Anomalous ELF phenomena in the Schumann resonance band as observed at Moshiri (Japan) in possible association with an earthquake in Taiwan

Inverse geophysical problems

Schumann resonance (SR) is the global electromagnetic phenomenon occurring in the Earth – ionosphere cavity at frequencies of 8, 14, 20 Hz, etc (the ELF band). Phenomenon was named after the author of the pioneer publication on the planetary resonance. Since natural electromagnetic signal originates from lightning strokes distributed worldwide, parameters of oscillations reflect the average condition of ionospheric plasma, spatial distribution and current intensity of thunderstorms. ‘Regular’ lightning strokes occur at a rate of 50 events per second, and their electromagnetic radiation forms the SR background. An irregular or transient component exists caused by relatively rare powerful strokes (the rate is about one event per minute or even less) that provide pulses ten times higher than an ordinary discharge. Three orthogonal field components (vertical electric and two crossed horizontal magnetic fields) are recorded at a Schumann resonance field site, and the power spectra are obtained in the frequency band up to 40 Hz averaged over a few minutes with the typical frequency resolution of 0.1 Hz. The main objective of report is to review the recent results in the Schumann resonance studies. The report consists of two parts; one of them summarizes the experimental data obtained during last 3 – 5 years, while the second describes model studies of ELF radio propagation. We try to mention the most important results in the Schumann resonance. The report surveys the data obtained by using ‘classical’ power spectra acquired at different observatories. Power spectra give information on the properties of the lower ionosphere boundary and on the dynamics of the global thunderstorms. For instance, the sudden changes can be detected in the space weather such as Solar Proton Events (SPE); the regular seasonal motion of thunderstorms is monitored, which is associated with the ground surface temperature; unusual changes might be found in the SR spectra prior to disastrous earthquakes, etc. The cross-spectra of both magnetic fields and magnetic and electric fields (Poynting vector) might be obtained when three field components are recorded. Cross-spectra enhance the coherent fields and reduce the noise thus presenting a more exact information on both the source location and the SR parameters. Elliptical polarization of horizontal magnetic field is measured via the cross-spectra technique, and recent comparison with the model computations proved the detection of Schumann resonance line splitting. Accumulated experimental data present a wide area for resolving the inverse electromagnetic problems directed to establishing an unknown instant distribution of the global lightning activity. Resonance parameters measured worldwide allowed for constructing the effective globally averaged models of the lower ionosphere and the dispersion relation for ELF radio waves. Recent model developments are connected with applications of finite element methods to the resonance problem. Simultaneously, the ‘classical’ spectral field representation was transformed into the time domain providing an effective computational algorithm. Analytical time domain solution allowed generating the quasi–random pulse successions modeling the ELF radio noise. The model time domain ELF signals might be synthesized with predetermined properties. In the conclusion of review, we note a renewal of interest towards the extra-terrestrial Schumann resonance studies. The Huygens probe mission on Titan stimulated interest to distant detection of feasible lightning strokes at the planets and their global location by using the planetary resonance concurrently with studies of ionospheres.

https://www.ursi.org/Proceedings/ProcGA05/pdf/E07.1(0262).pdf

Recent studies of Schumann resonance and ELF transients

Intensity of Schumann resonance oscillations and the ground surface temperature

We compare the dynamics of the intensity of the global electromagnetic (Schumann) resonance monitored in Japan with the global ground surface temperature (GST) over the period from November 1998 to May 2002. It is shown that the Schumann resonance (SR) intensity varies coherently with the ground surface temperature at mid-latitudes: the relevant cross-correlation coefficient exceeds 0.8. The linear correlation of data decreases with a decreasing latitude interval. We applied the principal component analysis (PCA) to distinguish inter-annual trends (anomalies) in the records from the periodic annual and semi-annual variations. The annual component of the SR intensity behaves similarly to the mid-latitude GST, while the inter-annual variations in the electromagnetic data are similar to those of the GST in the tropics. The regression analysis allowed us to obtain the analytical expressions relating the SR intensity with both the mid-latitude and low-latitude GST. Application of these equations allowed us to retrieve the observed SR pattern from the ground surface temperature and to “reconstruct” the variations in the tropical GST from recorded SR intensity.

Masashi Hayakawa

Papers

Schumann Resonance for Tyros

Inverse geophysical problems

Recent studies of Schumann resonance and ELF transients

Intensity of Schumann resonance oscillations and the ground surface temperature

Comparison of the variations in the intensity of global electromagnetic resonance and ground surface temperature