Lecturer: Dr Yasuhide Hobara (IRF-K) Date: 2005-02-03 10:00 Place: Aniara
Electromagnetic phenomena related to large earthquakes: Satellite and ground-based observations
The recent tsunami in south-east Asia due to a massive earthquake with a magnitude of 8.9 claimed an overwhelming number of innocent lives including many from Sweden. In addition to establishing a warning system for tsunami to minimize possible casualties, studying various electromagnetic effects around large seismic activity is a potential way of giving an early warning.
In this seminar, I will present some of my recent work related to the electromagnetic phenomena in association with large earthquakes observed either by ground-based or by satellite measurements. For example, ULF electromagnetic emissions are considered to be a very promising candidate for short-term earthquake prediction and the ionospheric perturbations associated with earthquakes leads us to a new science field so-called ?Lithosphere-atmosphere-ionosphere coupling?.
(1) ULF (Ultra Low Frequency) magnetic field: Ground-based measurement
We analyze the ULF magnetic field emissions observed at three different field sites. Large seismic events occurred near each station. Temporal dependence of the polarization ratio (ratio of horizontal to vertical magnetic field components) has been calculated in the frequency range between 1.17 mHz and 0.5 Hz with longer than 2-year data for each event. Two of three seismic events were associated with anomalous change in the polarization ratio. Remarkable similarities were found in the ratio between these two different seismic events: (1) The ratio has a significant increase about one month before the earthquake (about two times larger than usual level), (2) the increase is seen in the nighttime period (22~02 LT). The frequency range of increase in the ratio depends on the earthquake (0.01 Hz~0.022 Hz for the Izu Island earthquake swarms and 0.05 Hz ~ 0.1 Hz for the Guam earthquake). Calculated ratio based on the simple theoretical model has a good agreement with observed values for these two earthquakes.
Using PSD (Power Spectral Density) data on electron density and electric field variations observed on board Aureol-3 satellite at low-to-mid-latitude ionosphere we analyze a scale distribution of the ionospheric turbulence in a form k-?, where k is the wave number and ? is the fractal index. At first high-resolution data in the near-equator region for several orbits have been processed. In this case frequency range is from 6 Hz to 100 Hz (corresponding spatial scales from 80 m to 1.3 km), each power spectrum obeys a single power law fairly well, and the mean spectral indices are rather stable with ?N = 2.2Â±0.3, and ?E = 1.8Â±0.2 for the density and electric field, respectively. Then we produce statistical study of electric field bursts in the frequency range 10-100 Hz from low-time resolution data (filter bank envelope). These bursts concentrate aside of Equatorial Anomaly crest (geomagnetic latitude 30-40Â°) and their fractal indices vary in the interval ?E = 2.0 - 2.5. There is a weak systematic increase of their average intensity on about 3-4 dB during periods of seismic activity.
Created 2005-01-21 11:58:05 by Rick McGregor Last changed 2005-01-24 13:16:39 by Rick McGregor