IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS008 Oral Presentation 1978
ULF seismomagnetic signals analysis
Prof. Valery Korepanov
Laboratory for EM Investigations Lviv Center of Institute of Space Research IAGA
Baldev Arora, Fedir Dudkin, Gautam Rawat, Ashok Sharma
The existence of electromagnetic (EM) precursors of earthquakes (EQ) is widely discussed. The EQ EM
precursors in ULF band are the most promising between the known ones. They generally are based on
movement of conductive fluid or charges in the Earths magnetic field (inductive effect), piezoelectric or
piezomagnetic effects. However the problem of their reliable detection has not yet been solved first of
all because of low level of precursor signal and of the comparatively high level of ambient EM
interference. Many examples of their observations before the EQ are given in the scientific papers as
well as in many cases the EQ occur without preliminary EM activity. So, it appears that these precursors
are very different in their peculiarities and they vary not only at diverse places but also for different time
even in the same place. Apparently this fact depends on the specifics of geological formation and the
types of EM signal source in seismoactive zones and yields a rather modest progress in EQ prediction
practice. This report is an attempt to explain some experimental facts with observed seismogenic ULF
emissions. First the model of the source of EM variations connected with EQ preparation process is
proposed and discussed. It is shown that the range of distances for which the components of
anomalous EM field are detectable mainly depends on the signal-to-noise ratio at the observation place.
The approach to the determination of the EQ epicenter location is proposed based on multi-points
observations of ULF electromagnetic signals collected in the monitored area. The main principle of the
data processing using this method is based on the assumption that at relatively small distance between
EQ epicenter and observation points (no more than 100 200 km), we are always in near zone of
electromagnetic wave propagation what allows us to use as informative carrier only signal amplitude.
This peculiarity can be used for enhancing the signal-to-noise ratio by processing simultaneously the
time-synchronous signals collected in different points. To realize this efficiently, the critical requirements
to the observation system are discussed. The design features of the automatic ULF observation system
LEMI-30 with large dynamic range and free from time mismatch necessary for continuous monitoring of
EQ EM precursors are discussed and the example of its practical realization is presented. Some known
examples of ULF magnetic pre-EQ activity successful registration are analyzed and a new multi-points
observations results obtained with LEMI-30 systems in India during medium magnitude EQs at Koyna
active fault are reported. This study was partially supported by STCU grant 3165.
Keywords: electromagnetic, precursor, earthquake