The seismogenic area in the lithosphere considered as an 'Open Physical System'. Its implications on some seismological aspects. Part - III. Seismic Potential

Thanassoulas1, C., Klentos2, V.

1. Retired from the Institute for Geology and Mineral Exploration (IGME), Geophysical Department, Athens, Greece.
   e-mail: thandin@otenet.gr - website: www.earthquakeprediction.gr

2. Athens Water Supply & Sewerage Company (EYDAP),
   e-mail: klenvas@mycosmos.gr - website: www.earthquakeprediction.gr

Abstract.

The seismic potential of any regional seismogenic area is analyzed in terms of the “open physical system” inflow – outflow energy balance model (Thanassoulas, 2008, Part – I). Following the magnitude determination method presented by Thanassoulas, (2008, Part – II) any region of any arbitrary area extent is assumed as being a potential seismogenic region. Consequently, the capability for the generation of a maximum magnitude future EQ at each virtual seismogenic region is investigated all over Greece at certain times. The later results are used to compile maps of the seismic potential / maximum expected EQ magnitude for Greece at 5 year’s intervals ranging from 1970 to 2000. The comparison of these seismic potential maps / maximum expected EQ magnitude to the corresponding seismicity (M>6R) for each corresponding 5 years period reveals their tight interrelation. Therefore, the calculated seismic potential / maximum expected EQ magnitude, due to its drastic change in time in any seismogenic region, is a dynamic in time parameter which indicates the seismic energy charge status of each seismogenic area.

1. Introduction.

The terms “seismic hazard” and “seismic risk” are, very often, referred to in the seismological and engineering geology studies. The term “seismic hazard”, at any place, refers to a quantity (H), its magnitude being the expected intensity of the ground motion at this place. The later, can be expressed as (Papazachos et al 1985, 1989, Tselentis 1997) the expected ground acceleration, ground velocity, ground dislocation and the expected, macroseismic intensity (l).
The term “seismic risk” (R) refers to the expected results (damages in buildings, deaths etc) from the occurrence of an earthquake and depends strongly on the seismic hazard of the same place. The term (R) of the seismic risk can be expressed as the convolution of the seismic hazard (H) to the vulnerability (V) of a technical construction. Therefore, the following equation holds:

R = H * V

            (1) 

Tselentis (1997) presents the following, holding equation for the seismic risk:

R = H(e, μ, s)*T

  (2) 

Where, (R) is the seismic risk, (H) is a non-linear parametric (e, μ, s) equation with (e) being the earthquake source parameters, (μ) is the propagating elastic waves media, (s) is the local conditions and (T) is the vulnerability of the technical constructions. A seismic risk study, at a certain place, has a strong probabilistic – stochastic character and therefore all parameters that can contribute to an excess ground motion at a probabilistic level, are taken into account. The results of a seismic risk study are presented in various forms. Probabilistic graphs vs. Mercalli scale, excess of spectral velocity and maps of spatial distribution of expected ground velocity are some of them. A typical, seismic risk study of a place includes (Tselentis, 1997) the four following basic steps:

• Identification of the near-by earthquake sources.

• Determination of the statistical model that prescribes the earthquake sources and the expected, maximum magnitude due to each one of them.

• Determination of the best amplitude decay of the seismic waves of each seismic source.

• Determination of the probability for non-exceeding any ground motion parameter level.

Maps of the spatial distribution of seismic hazard of Greece were presented in the past (Makropoulos et al. 1985, Papazachos et al. 1985, 1989). Furthermore, the Greek territory was divided in four (I, II, III, IV) zones of different expected ground acceleration, as a function of the recurrence mean time value, and the intensity (I) of a future, seismic event. This particular former seismic hazard map of Greece is presented in the following figure (1).

Fig. 1. Former, seismic hazard zoning is presented for the Greek territory (Papazachos et al. 1989, OASP).

This map has already being revised, due to the large seismic events that took place in Greece, during the last decade (1990 – 2000). The new map is divided into three zones and presents a close resemblance to the one of figure (1).
Following the mathematical analysis which is presented by Papazachos et al. (1989), it is made clear that the seismic hazard map of Greece is based mainly on probabilistic seismic data, as far as it concerns the parameters of the earthquake sources. T

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