1. INTRODUCTION.

   An earthquake (EQ), in terms of physics, is an abrupt, strain energy release in the form of kinetic energy that had been accumulated in a seismogenic area. The science which studies these physical phenomena is called “seismology”. This term is formed by the combination of two Greek words. The first one is the word “seismos” which stands for the word “earthquake” and the second one is the verb “lego” which in the Greek language means “talk about”. Seismology, at its early stages, developed from the necessity of people to know in advance when an earthquake is going to occur, since strong earthquakes hit, some times, abruptly, devastating populated areas, damaging cities, villages and moreover killing people. Seismology, in the course of its evolution, was divided into two main branches. The first but less developed, is its initial main task, namely the prediction of an earthquake. The second one, which developed rapidly and in great depth, is the study of the Earth’s interior through the analysis of the propagation of the seismic elastic waves in the ground, waves generated by the occurrence of earthquakes.
   Although seismological observations are referred back to ancient Greek writers, its scientific effectiveness was boosted during the last 100 years, when instrumental seismology was introduced. The mechanism that controls the generation of an earthquake is not yet well known. Many theories have been suggested, starting with the early “Elastic Rebound Theory” (Reid, 1911), SOC theories (Main 1995, 1996), where the seismogenic area can produce an earthquake by a slight variation of its stress level, up to the latest one which states that an earthquake is “a frictional phenomenon rather than a fracture one” (Scholz, 1998). In any case, it is generally adopted that when the stress of a seismogenic area exceeds a threshold level then, regardless the mechanical procedure followed for the specific rock fracture / friction slip, an earthquake takes place. The absence of a physical model for the process of seismogenesis poses more difficulties in the solution of the particular problem of earthquake prediction in terms of Classical Seismology or Statistical Physics.
   The term “earthquake prediction” refers to the knowledge of the earthquake prognostic parameters that is the location, the time of occurrence and its magnitude, for some time before it takes place. According to the prognostic time window it is distinguished as: long-term, referring to a time window of some decades of years, medium-term, referring to a time window of a few years (2-3) and short-term, referring to a time window of the order of up to a couple of months, while sometime the term “immediate” is used when the time window is of the order of a few days.
   The scientific literature which concerns the topic of earthquake prediction has to present a very large number of papers which deal with it. Each one of them deals with some “predictive” technique or probable physical observation which could help in to the solution of this problem. There is no point to refer to them in this book, since these can be found easily in almost all the seismological, scientific journals, published internationally. Furthermore, a search in the bibliography indicates that a lot of monographs exist which deal with this topic, either in the form of textbooks or as proceedings of scientific meetings, dedicated, to this specific topic. After a quick survey in public libraries and bookstores through their web portals, the following bibliography was traced under the title “Earthquake prediction”, or very similar to this one: Tsuboi et al. 1962, Rikitake 1976, Wyss et al. 1978, Vogel 1979, Wyss 1980, Keilis-Borok, (1980), Rikitake 1981, Asada 1982, Simpson and Richards 1982, Toshi and Ohnuki 1982, Vogel and Itsikara 1982, Rikitake 1982, Rikitake 1984, Mogi 1985, Stuart 1985, Shimazaki and Stuart 1985, Guha and Patwardhan 1985, Tyckoson 1986, Kisslinger 1986, Association for the Development of Earthquake Prediction (Japan) 1986, Keiiti and Stuart 1988, Stuart and Aki 1988, Ma et al. 1990, Dragoni et al. 1992, Tazieff 1992, Shih-jung 1993, Hayakawa et al. 1994, Lomnitz 1994, Bonnet et al. 1995, Gokhberg et al. 1995, Lighthill 1996, Dmowska 1997, Keilis-Borok et al. 2003, Donnellan 2004, Varotsos 2005, Saumitra 2006, Mukherjee 2006 just to name the textbooks found which were published during the last 45 years that, more or less, represent along time, the advances in the topic of earthquake prediction.
   The earthquake prediction evolution in time is described in details by Geller (1997), who concludes that despite research has been conducted for more than 100 years, “no obvious” success has resulted. The question that arises is what the cause of this failure is. In a very general approach this is discussed and commented with the use of the following sketch (fig. 1.1).                                                            

Fig. 1.1. Generalized flow chart indicating the procedure followed towards the earthquake prediction. A = input data, B = methodology used / physical model etc, C = wanted output, x, y, t, m are the prognostic parameters for all the types of EQ prediction (x, y stand for EQ coordinates in any appropriate coordinating system, t stands for the time of the EQ occurrence and M stands for the EQ magnitude).

   Figure (1.1) shows the generalized procedure, used to date, by the various researchers to solve the earthquake prediction problem. The wanted output (C), that is the prognostic parameters of the output of the system (EQ prediction), depends on the procedure / methodology (B), used, and the input data (A). So far this system has failed or has presented very limited success. Therefore, its failure must be attributed either to part (A) or to part (B) or to both of them. It is suggested that, part (B) is highly unlike to fail, since it consists mainly of mathematically validated, robust, statistical methods. At the same time part (A) is valid, too, since it consists of the seismological data, collected, by the different seismological obser-vatories and there is no doubt about their validity. This peculiar non-conformable situation can be explained only with the assumption that part (A) and (B) are not compatible in terms of physical laws. In other words these refer to different physical quantities/procedures that cannot be interrelated with any rational physical / mathematical model.
   The incompatibility of figure (1.1) leads us to the selection: at first of a new data set as (A) and secondly to a different methodology / procedure (B) which will be used for the processing of the input data. The latter, additionally, dictates new physical models to be adopted and to be used in the physical / mathematical analysis of the earthquake prediction problem. If all these are valid and true, then the relation between A, B, C will be a valid one and the problem will have, in principle, been solved. A final remark to be made is that the data used as input must intrinsically, even in a hidden way, convey the information of location, time and magnitude of a future earthquake.
   The aim of this book is exactly this: to present the implemented earthquake prediction deterministic, specific procedure, which fulfills the layout diagram, presented in figure (1.1). To this end, different physical models are introduced, which are related to the seismicity of a seismogenic area and allow us to use conventional, physical laws and mathematical analysis for the calculation of the individual prognostic parameters.
   The main difference between this book and the aforementioned bibliography is that in this book all the prognostic parameters (time, location, magnitude) are concerned with deterministic methods, while traditional, statistical methodologies are used at minimum and only for the purpose to analyze the validity of the obtained results from the postulated, physical models. Moreover, it analyses the earthquake prediction topic in the range of what is called by the seismologists as “short-term prediction” and considered, by them, as an impossible target. On the contrary, in the existing to date bibliography, just one monograph was traced which refers to “medium term prediction” (Kejiti and Stuart, 1988), while the majority of these books is related to time prediction, some times the topic of location, in terms of a regional seismogenic region, is treated, in a stochastic way and very rarely to the prognostic parameter of magnitude. It is hoped that other researchers will follow this research path and will improve and refine the topics which are presented in this book.
   In all these years of my involvement with earthquake prediction, the people who were interested in this topic put a question to me quite frequently. Are all the earthquakes predictable? Well, the answer is definitely, no. First of all, magnitude plays a great role in predictability. As long as the magnitude of a future earthquake increases, more energy is going to be released, the more the physical properties of the seismogenic area are affected prior to the seismic event and therefore, there is larger probability, for the affected physical properties of the seismogenic area, to become observable above ambient noise. The depth of occurrence is another parameter that affects the earthquake predictability. The depth of occurrence of an earthquake is of vital importance for the generation of precursory physical variations in the seismogenic area, since the physical parameters that prescribe the underground status of the Earth change drastically according to the depth. Consequently, the earthquakes which occur in favorable depth and geological / tectonic environment, capable of producing valid, precursory phenomena, are predictable. We will come back on this topic in the course of this presentation.
   The implementation of the prediction of a strong earthquake depends on the generation of the appropriate precursors before its occurrence. These precursors must convey or must be capable of providing, probably after appropriate processing, at least one of the prognostic parameters of the pending earthquake. Therefore, in the course towards a successful prediction, it will be necessary to use different types of precursors and / or different analyzing procedures, as well as different physical models that will be interrelated, so that a valid prediction may be achieved. The writer followed this philosophy, which is presented in details in this book.
   In the course for the earthquake prediction and particularly in the search for an effective earthquake precursor, many different physical quantities and mechanisms have been studied. Some of the observations which had been made before strong earthquakes occurred are: the seismic gap, that is the absence of normal seismicity in a seismogenic area for a long period, the seismic quiescence that is the drop of seismicity below its normal level, the doughnut feature of spatial distribution of earthquakes around the epicenter area, the earthquake swarm that precedes a large earthquake, the change in Vp / Vs ratio over the seismogenic area, the various time-spatial statistical earthquake patterns, observed, the change in Earth resistivity, the change of b value of the Gutenberg-Richter law, the emission of electro-magnetic waves, the increase of Radon emission from the ground, the geodetic variations (abnormal ground elevations), the change in the chemical composition of the underground waters, the change in temperature of the aquifers, the changes of the Earth’s magnetic field, the changes of the Earth’s electric field, the observed changes of the plasma density in the ionosphere, the strange animal behavior, to name some of the most important and well-known of them.
   All these observations indicate that earthquake precursory phenomena are generated in most of the physical – geological processes on Earth, in the seismogenic region, due to the fact that the strain accumulation in it changes its physical – geological / tectonic properties. The real problem with the detectability of the various precursors lays in the fact that the precursors, in most cases, are of low level, relatively to ambient conditions, and therefore, they are masked by this noise or lay out of the available, instrumental capability to detect them, very easily. This leads to the necessity to develop new precursory signals, processing procedures, as it has been done in the case of seismic precursory, electrical signals and will be presented in the sections to follow.