**5. Conclusions**

The results carried out in this paper are based on the hypothesis according to the preseismic conductivity changes, due to the fluid migration through faulting system, may generate increased values of the normalized function Bzn proportionally with the intensity of anomalous current concentrations through CECA.

Earthquakes Precursors 97

This work was supported by the CNCSIS - UEFISCDI, project number 1028/2009, PN II – IDEI code 14/2008. We would also like to thank to the Institute of Geodynamics of the Romanian Academy for providing electromagnetic data and facilities for the present

Bahr, K. (1988). Interpretation of the magnetotelluric impedance tensor: regional induction

Brace, W.F.; Orange, A. S. & Madden, T.N. (1965). The effect of pressure on the electrical

Fenoglio, M.A.; Johnston M.J. & Bierlee, J.D. (1995). Magnetic and electric fields associated

Fraser-Smith, A.C.; Bernardi, A.; Mc Gill, P.R.; Ladd, M. E.; Halliwell, R.A. & Villard, Jr.

Freund, F. (2000). Time-resolved study of charge generation and propagation in igneous

Girbacea, R. & Frisch, W. (1998). Slab in the wrong place: Lower lithospheric mantle

Gotoh, K.; Akinaga, Y.; Hayakawa, M. & Hattori, K .(2002). Principal component analysis of

Gvirtzman, Z. (2002). Partial detachment of a lithospheric root under the southeast

Hattori, K..; Serita, A.; Yoshino, C. Hayakawa, M. & Isezaki, N. (2006). Singular spectral

Hayakawa, M. & Fujinawa, A.Y. (1994). *Electromagnetic Phenomena related to Earthquake* 

Hayakawa, M. & Molchanov, O.A. (2002). *Seismo-Electromagnetics: Lithosphere-Atmosphere-Ionosphere Coupling,* Terra Scientific Pub. Comp., ISBN 9784887041301, Tokyo Ismail-Zadeh, A.T.; Panza, G.F. & Naimark, B.M. (2000). Stress in the descending relic slab beneath the Vrancea region, Romania, *Pure Appl. Geophys.,* 157, pp.111-130

M 7.1 Lomma Prieta earthquake. *Geophys. Res. Lett.,* 17, pp.1465-1468. Freund, F.; Gupta, A.; Butow, S.J. & Tenn, S. (1999). Molecular hydrogen and dormant

resistivity of water-saturated crystalline rocks. *Journal of Geophysical Res.*, 70 (22),

with changes in high pore pressure in fault zones: application to the Loma Prieta

O.G. (1990). Low frequency magnetic field measurements near the epicenter of the

charge carriers in minerals and rocs, In: *Atmospheric and ionospheric electromagnetic phenomena associated with earthquakes,* Hayakawa, & Molchanov, pp. 839-871, Terra

delamination in the last stage of the Eastern Carpathian subduction retreat. *Geology* 

ULF geomagnetic data for Izu island earthquake in July 2000. *J.Atms. Electr.* 22,

Carpathians: toward a better definition of the detachment concept. *Geology* 30, pp.

analysis and principal component analysis for signal discrimination of ULF geomagnetic data associated with 2000 Izu Island earthquake swarm. *Phys. Chem.* 

and local telluric distortion, *J. Geophys.,* 62, pp.119-127

ULF emissions. *J.Geophys.Res.* 100, pp. 12951-12958

rocks. *Journal of Geophysical Res.,* B, 105, pp.11001-11019

**6. Acknowledgment** 

research project.

**7. References** 

pp. 5669-5678

Sci. Publ. Comp., Tokyo

26, pp.611-614

*Earth,* 31, pp. 281-291

*Prediction*, Terra Scientific Pub. Comp, Tokyo

pp.1-12

51-54

The normalized function Bzn carried out at GOPS has been analyzed in order to detect its pre-seismic anomalous behaviour related to the intermediate depth earthquakes with M 4. Before all the earthquakes of M 4 the Bzn distribution exhibit significant enhancements from the normal trend and the pre-seismic lead time is about 7-15 days. The Bzn average value of 1.842 (Fig.9), associated with earthquakes of M≤3.3 occurred on the period January 16 – March 7, represents the threshold limit between the normal trend and its pre-seismic anomalous behaviour, taken as possible earthquake precursor.

When anomalous behavior and normal trend domains are much closed, as a multitude of earthquakes of different magnitude occurred at short time intervals, then a superposition effect has been observed.

For the Vrancea zones, two correlations between the magnitude of seismic events and Bzn are highlighted (Fig.14):


Sometimes, superposition effects may generate exceptions to the above rules.

As this methodology allows us to know always the structure changes after any seismic event (on the base of dimensionality parameters), what permit to use further on the most adequate electromagnetic techniques, it becomes an interesting subject of studying the earthquake mechanism and the associated electromagnetic precursors.

Fig. 14. Distributions of the normalized function Bzn and earthquake magnitude on the 2009 analyzed interval; blue circles are earthquakes with M< 4; red circles are earthquakes with M 4; red dashed line represents the limit above to which one earthquake of M 4 is possible to occur.

The normalized function Bzn carried out at GOPS has been analyzed in order to detect its pre-seismic anomalous behaviour related to the intermediate depth earthquakes with M 4. Before all the earthquakes of M 4 the Bzn distribution exhibit significant enhancements from the normal trend and the pre-seismic lead time is about 7-15 days. The Bzn average value of 1.842 (Fig.9), associated with earthquakes of M≤3.3 occurred on the period January 16 – March 7, represents the threshold limit between the normal trend and its pre-seismic

When anomalous behavior and normal trend domains are much closed, as a multitude of earthquakes of different magnitude occurred at short time intervals, then a superposition

For the Vrancea zones, two correlations between the magnitude of seismic events and Bzn

ii. anomalous behaviour of Bzn 1.854 may be use as pre-seismic value for an earthquake

As this methodology allows us to know always the structure changes after any seismic event (on the base of dimensionality parameters), what permit to use further on the most adequate electromagnetic techniques, it becomes an interesting subject of studying the earthquake

Fig. 14. Distributions of the normalized function Bzn and earthquake magnitude on the 2009 analyzed interval; blue circles are earthquakes with M< 4; red circles are earthquakes with M 4; red dashed line represents the limit above to which one earthquake of M 4 is possible

anomalous behaviour, taken as possible earthquake precursor.

i. earthquake of M 4 is expected to occur when Bzn 1.847;

mechanism and the associated electromagnetic precursors.

Sometimes, superposition effects may generate exceptions to the above rules.

effect has been observed.

are highlighted (Fig.14):

of M 5.

to occur.
