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| Titel |
Still one evidence of the local ULF lithospheric magnetic activity before Mw=9.0 Tohoku earthquake |
| VerfasserIn |
Fedir Dudkin, Valery Korepanov, Denys Dudkin, Yasuo Ogawa |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250071920
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| Zusammenfassung |
| The ultra low frequency (ULF) lithospheric magnetic activity in the frequency range below 1
Hz is recently considered as one of the most informative evidence of an earthquake
preparation process. However, the detection of such an activity meets some serious
difficulties being touched the separation of such signals on the background of comparatively
very intensive Pc3-Pc5 ionospheric/magnetospheric signals. Another hard problem is
localization of signal source at so low frequencies.
For overcoming these obstacles the space selection method was developed in the
Laboratory of Electromagnetic Investigations (LEMI) of Lviv Centre of Institute for Space
Research. This method is based on synchronous data processing from two or more spaced
magnetometers with use of magnetic field polarization ellipse technique. The method can be
effectively applied to detection just a lithosperic magnetic activity and its separation from
ionospheric/magnetospheric one [1].
The topic of keen interest is to apply this technique at the study of the pre-earthquake
lithospheric magnetic activity for one of the greatest recent Earth’s shock that was happened
in Japan. On March 11, 2011 at 05:46:24 UTC the undersea megathrust earthquake hit the
eastern coast of Japan with magnitude Mw=9.0 (so-called Tohoku earthquake). Its epicentre
was in the point 38.30Ë N, 142.37Ë E with the nearest distance to Japan coast about 70 km.
The hypocentre was at depth 29 km.
The data from two 3-component fluxgate magnetometers with sampling rate 1 Hz for
period from January 1 to March 22, 2011 have been analyzed. The magnetometers are
located in Esashi (ESA) geomagnetic observatory and Akasaka (AKSK) temporary
measuring site with coordinates 39.18Ë N, 141.75Ë E, 39.24Ë N, 141.36Ë E
respectively. The fluxgate magnetometer in AKSK site is a part of the long-period
magnetotelluric station LEMI-417M. The distance between measuring points is about 35
km, while the mean distance from them to the epicenter of Tohoku earthquake is
approximately 125 km. At application of the polarization ellipse technique the procedure
of so-called blind search have been used to the rectangular monitored area with
coordinates 38.19Ë N - 39.63Ë N and 141.51Ë E - 142.56Ë E, which includes the
Tohoku earthquake epicentre. The monitored area 160x90 km with depth 0-70 km
was decomposed into 8064 subblocks 5x5x5 km of total volume about 1,008,000
km3.
The pre-earthquake ULF lithospheric magnetic activity and peculiarities of its distribution
in space, time and frequency areas in the monitored region have been analyzed. The
obtained results on the background of the Kp index values will be discussed and
presented.
1. Dudkin, F., Korepanov, V., Magnetic Field Polarization Ellipse: A New Approach for
Detection of Pre-Earthquake Lithospheric Activity, Chapter in book “The Frontier of
Earthquake Prediction Studies”, 212-244, Japan, Tokyo, 2011. |
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