Short-term Earthquake Prediction Based on Seismic Precursory Electric Signals Recorded on Ground Surface.
“What today seems impossible, is tomorrow’s reality”
Dear visitors of this page:
We inform you that this page is specifically addressed to Universities (Seismology Dept.) and to Seismology Research Institutes already involved in the topic of "Earthquake Prediction".
A historical flash-back:
In 2003, fifteen (15) years ago, the prototype of a complete "Pre-seismic Electric Signals" data acquisition system was constructed and put in operation in three monitoring sites in Greece in the frame of a short-term earthquake prediction experiment that lasted for nine years 2003 - 2012 (see more details elsewhere in the present site).
The initial set-up consisted of different hardware components that could be easily constructed and obtained from the electronic components market taking in to account the available technology during these years (Fig. 1).
Fig. 1. Block diagram - flow chart of the prototype.
From the first initiation of this site (2003) up to day (2018) many visitors of it expressed their interest and asked questions about the methodology used and the data acquisition system, that is the true core of the used methodology (reliable observation data is the basis of every physical phenomena study).
Triggered by the specific request, of a seismogenic country University, to supply them with a number of complete hardware units, a drastic update, with the cutting edge today's electronic technology, of the original prototype was utilized by the "Crisistech Labs". The new hardware is an "All in One" unit presented in the following Fig. 2, 3
Fig. 2 Front End (click on icon for detailed technical description).
Fig. 3. Rear End (click on icon for detailed technical description).
Some useful information concerning the monitoring stations field set-up.
1. How many monitoring sites should a network consist of?
The case of one (1) monitoring site.
The answer is definitely NO. See an example in the following figure (4).
Fig. 4. Azimuthal direction calculated by an "in-coming signal" (on different time) at HIO and ATH monitoring sites.
The first problem posed to the researcher is whether the recorded signal is a preseismic signal or a "noise" one. Moreover, in the case of a preseismic electrical signal there is no way to know the distance: monitoring site - EQ epicentral area. Therefore the use of only one single monitoring site is useless.
The case of two (2) distant monitoring sites.
In the following figures (5, 6, 7) preseiemic electrical signal were recorded by two distant monitoring sites (PYR and ATH) and the calculated epicentral area (blue circles) is compared to the EQ epicenter calculated by seismological methods. .
Fig. 5. Use of two distant monitoring sites (PYR and ATH).
ATH - EQ distance = 390 Km. PYR - EQ distance = 576 Km.
Another example is shown in the following fig. (6).
Fig. 6. Use of two distant monitoring sites (PYR and ATH).
ATH - EQ distance = 185 Km. PYR - EQ distance = 212 Km.
A last example is shown in the following fig. (7).
Fig. 7. Use of two distant monitoring sites (PYR and ATH).
ATH - EQ distance = 286 Km. PYR - EQ distance = 130 Km.
Human made or industrial noise is more or less a local noise, therefore it cannot interfere the recordings of a distant monitoring site. Consequently, converging signals recorded simultaneously at distant monitoring sites are most probably, preseismic electric signals except in the case of no convergence (parallel electrical azimuthal direction) that is the case of ionospherically induced currents (Fig. 8).
Fig. 8. Example of two distant monitoring sites (PYR and ATH) that record an ionosperic signal induced in the ground.
In the case of a real EQ prediction experiment either the pending EQ epicentral area is already known from its historical seismicity or generally it is unknown.
- Known pending EQ epicentral area. In this case three (3) monitoring sites are required to monitor the epicentral area as the field set-up presented in the following fig. (9).
Fig. 9. Pending EQ known epicentral area monitored by three (3) monitoring sites (optimum field set - up).
The drawback of this approach is that even if the past seismic history is known there is no method to achieve a short-term time prediction for the specific seismogenic area. Consequently, there is a high degree of failure of the experiment due to a possible long delay of the EQ occurrence, caused by unknown physical reasons. Moreover this field set-up focus on a specific epicentral area and ignores other ones far distant from it.
A better field set-up approach is the following, already used in Greece. Three (3) monitoring sites form a line array that monitors the entire regional wide area. The latter is presented in the following fig. (10) as it was applied in the Greek territory.
Fig. 10. In - line array of three monitoring sites (PYR, ATH, HIO).
Left: ATH - EQ distance = 273 Km. PYR - EQ distance = 53 Km. HIO - EQ distance = 466 Km
Right: ATH - EQ distance = 272 Km. PYR - EQ distance = 480 Km. HIO - EQ distance = 10 Km
The main advantage of this set - up is that no previous knowledge of the epicentral area is required. The previous examples of fig. (5, 6, 7) show that the entire Greek seismogenic area is completely monitored by only three (3) monitoring sites. Therefore, the triangulated preseismic electrical signal will enable the determination of the epicentral area of the pending EQ. Moreover, will indicate that the specifically already calculated seismogenic area has entered in the last phase time period of the EQ occurrence (short-term EQ prediction).
There is a drawback in this set-up, too. When the pending EQ happens to occur along the line array direction (see fig. 10) then the error of the epicentral area estimate is very large due to the fact the determined electrical vectors are almost parallel.
The solution of this problem is to use simultaneously of two (2) orthogonal line arrays in the following (Fig. 11) field set - up:
Fig. 11. Orthogonal line arrays. W - E consists of M4, M1, M5. and the N - S consists of M3, M1, M2.
As a result of this presentation it is clear that the minimum number of monitoring sites required to cover an extended seismogenic country is five (5). The latter can be expanded i.e. to a large grid of 400x400 Km grid-cell. For the Greek case a number of nine (9) monitoring sites (see fig. 12) was planned to be installed but this task proved to be beyond our financial and available volunteers to maintain in operation such a project.
Fig. 12. Monitoring network field - setup proposed to cover the entire Greek territory by nine (9) monitoring sites. Array (1) = KER, THE, EVR. Array (2) = PYR, ATH, HIO. Array (3) = CRW, CRE, ROD.
1. What should the dipole length be?
The capability of a dipole to identify an incoming signal depends on its length. For a given electrical field strength (J) the following formula holds:
J = dV / L
where: J = electrical field strength, dV = measured voltage across the dipole and L = dipole length. Consequently, if larger values of dV are needed then larger L should be used. Satisfactory results were achieved in Greece with the following dipole lengths: PYR = 160m, ATH = 20m, HIO = 200m.
2. At what distance between the epicentral area of an EQ and a monitoring site location can preseismic electrical signals be identified?
Results from fig. (5, 6, 7) show the following:
ATH monitoring site (dipole length = 20m): has identified preseismic electrical signals at distances of 286, 185, 390 km.
PYR monitoring site (dipole length = 160m): has identified preseismic electrical signals at distances of 130, 185, 576 km.
Results from fig. (10) show the following:
HIO monitoring site (dipole length = 200m): has identified preseismic electrical signals at a distance of 468, km .
Therefore, a grid of 400 x 400 km consisted of 200 m dipoles is recommended as a generalized field set-up approach.
3. Geological environment of the monitoring sites.
Dipoles should be installed on a homogeneous electrical ground of low resistivity values. It is highly recommenced the geological environment of Tertiary - Quaternary formation. Moreover, the dipoles must NEVER IN ANY CASE CROSS different resistivity geological formations.
For further scientific inquiries contact Dr. Thanassoulas, C. at : email@example.com
For technical - hardware and purchase inquiries contact Tsutas. A at : firstname.lastname@example.org