Liviu Constantinescu and D. Enescu
Abstract
By using direct energy determinations, in the first part of this paper, the authors indicate that in the case of the intermediate Vrancea earthquakes, the energy-magnitude relation of Gutenberg and Richter
log E = 11.8 + 1.5 M
can be applied, while on the basis of the data presented in Table 1, the following formulae:
log rb = 0.77 M + 2.89 for 4< M<7
log rb = 0.51 log E – 3.16
are calculated, where: r is the radius of the rupture surface at the focus
b – the value of the relative displacement of the faces of this surface (modulus of Burgers' vector).
Knowing the intensity I0 at the epicentre and the energy E for 28 earthquakes
(Table 2) the following formula was determined:
log E = 15.56 + 0.75 I0
by means of which the authors estimated the energy of the strong earthquakes
during 1470 – 1908 (Table 2) when the I0 value was known.
By employing the estimated relations, the E- and rb-values as well as the energy
class K have been determined for 377 earthquakes recorded by the Romanian seismographic
stations during the 1937 – 1962 period, and for 12 earthquakes – having
M>5 – produced within the 1908 – 1937 period.
In the second part, on the basis of the results presented in Tables 3 and 4,
the following formulae have been computed:
log 
= 5.72 – 0.49 K
for K = 10; 10.5; 11.5 ….. 16
log = 6.18 – 0.51 K
for K = 10; 11; 12 ….. 16
and log = 3.69 – 0.76 M
for 3.5<M<7.5
where is
the average number of earthquakes of a certain energy class K or of magnitude
M, produced during one year.
The authors have studied the errors and obtained the values of the mean square
error 
and of the dispersion 
of the repetition of earthquakes with respect
to the ideal periodicity.
For the parameters of the seismic regime, following values were obtained:
– in the case K = 10; 10.5; 11; 11.5 ….. 16
=
0.49; A11 = 2.2 / year; Raverage = 0.194;
– in the case K = 10; 11; 12; … 16
=
0.51; A11 = 3.7 / year; Raverage = 0.235.
Considering the surface of the epicentral region as having about 2000 square
km, the values for the seismicity S and the "tectonic flux" F were
obtained:
S = 1.68 x 10E+18 erg. /(squareKm year)
F = 1.8 x 10E+7 erg
/
(squareKm year)
For the calculation both the S and the F values, the period 1937 – 1962 was chosen, because it presents the most complete data on the quantity of energy liberated by the Vrancea foci.