**5. References**

214 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

1 f 1 f 2 f 2 f

(8) f f / / f f 

( i 1, 2), the equation,

**4. Conclusions** 

/

 

, so for 0 and 0 cases 2 1

, can be deduced. Thus we get that 2 1 >1 all the

In generally, <sup>f</sup> . From formulae (8), 1 1 <0 and 2 2 <0 when 0 , and they will decrease with going bigger, which could be why most AR anomalies in/nearby the epicenter region in the late preparation stages of strong EQs are commonly a drop-type pattern; And 1 1 >0 and 2 2 >0 when 0 , and they increase with decreasing. This is coincident with the physical analysis. Because 1 , in formulae

when the AR changes of channels X and Y, sx sx and sy sy , are all increased or decreased. This is coincident with the physical meaning of inequality (5). Let i i t

In general, it can be seen that anisotropic TR changes is obviously associated with <sup>f</sup> , and , which is clear in theory, and anisotropic AR changes arise from anisotropic TR changes. Therefore, the reason for AR changes and their anisotropic changes as well as their

1. The AR changes related to the late preparation process of strong EQs are indeed recorded in china. The two proofs are as follows: (a) Reappearing AR changes are observed before two great EQs. (b) Two strong EQs are successfully predicted using AR changes observed at stations nearby on an one-year time scale, which three elements,

2. Of 41 stations in or nearby the epicentral areas of 27 strong EQs, for over 95% stations the anisotropic AR changes are related to the maximum compressional stress directions of the EQ focal mechanism solutions. Their behaviors are: the most prominent AR change appears perpendicular or nearly perpendicular to the direction. The relationship between the anisotropic changes and the direction is well coincident with the directional AR changes in the loading process of most rock (soil) samples. And the relationship can be explained in theory. Therefore, we can confirm that the anisotropic AR changes which are directly associated with the later preparation processes of strong

3. The reasons for AR changes and their anisotropic changes as well as their pattern (droptype or rise-type) are clear. The compressional action along the maximum compressional stress direction plays an important role in/nearby the EQ focal region in the later preparation stages of strong EQs. This caused that the micro cracks in the underground medium develop fast in number, and their strikes are predominant along the direction, as a result, conductive aisles in the medium are linked each other and

 2 f

time. This is coincident with the physical meaning of inequality (7).

such as locations, magnitudes and year 2003, are all right.

EQs are truly recorded nearby epicentral regions.

1 f 

pattern (drop-type or rise-type) are clear in theory also.

2

. (8)

2 1 

>1 all the time

/


**1. Introduction**

science!

In recent years, the wind prevailing in the scientific community does not appear to be favourable for earthquake (EQ) prediction research, in particular for the research of short term prediction [1]. Sometimes the arguments were extended to the extreme claim that any precursory activity is impossible [2]. Considering the difficulties associated with such factors as the highly complex nature, rarity of large EQs and subtleties of possible preseismic signatures, the present negative views are not groundless. It is difficult to prove associations between any two events (possible precursor and EQ) separated in time. To a certain extent, the aforementioned negative views were due to the fact that in the last decades the study of seismic precursors was expected to lead in a relatively short period of time to EQ prediction. However, the EQs are nothing but physical phenomena, and science should have some predictive power on their future behaviour of any physical system. In spite of this scepticism of the scientific community, the research towards the possible prediction of EQs in the future continues. This is attempted now with a more critical view taking into account new ideas and performing detailed theoretical, laboratory, field, and numerical investigations. Significant progress has been made in the research of precursory pattern changes of seismicity (e. g., Wyss and Martirosyan,[3]; Huang et al. [4]; Huang [5]) and the intermediate-term prediction of large EQs world-wide is already in the statistically proven stage (e g., Kossobokov et al. [6]). More recently, even the efforts to shorten the lead time to the "short-term" range are being made (e. g., Keilis-Borok et al.[7]). Some significant new waves have been rising in EQ

**Are There Pre-Seismic Electromagnetic** 

**Precursors? A Multidisciplinary Approach** 

*University of Athens, Faculty of Physics, Department of Solid State Section,* 

**11**

*Greece* 

Konstantinos Eftaxias

*Panepistimiopolis Zofrafos, Athens* 

An EQ is a sudden mechanical failure in the Earth's crust, which has heterogeneous structures. The use of basic principles of fracture mechanics is a challenging field for understanding the EQ preparation process. A key fundamental question in strength considerations of materials is: *when does it fail?* Thus, a vital problem in material science and in geophysics is the identification of precursors of macroscopic defects or shocks. It is reasonable to expect that EQ's preparatory process has various facets which may be observed before the final

The present contribution focuses on fracture induced electromagnetic (EM) fields, which allow a real-time monitoring of damage evolution in materials during mechanical loading. Crack propagation is the basic mechanism of material failure. EM emissions in a wide frequency

catastrophe. *The science of EQ prediction should, from the start, be multidisciplinary!*

