ff3 fs4 fc0 sc0 ls1 wsd">sion equations averages, we were able to determine a
general equation which allows us to make an estimate of
the region’s local magnitude and any possible errors as-
sociated to it:

D
M2.1530.072 LogD1.9250.132  (3)
From the Equation (3), we calculated the magnitude
for all 137 events selected and by performing an analysis
with the aid of the graphics, the linear regression equa-
tions for each station, along with the errors related to
them (the stations), we noticed that the stations present
some variation in the record of both the maximum
Copyright © 2012 SciRes. IJG
Í. L. DE OLIVEIRA ET AL.
224
Figure 4. Graph ML × LogD at station Jan03.
Figure 5. Graph ML × LogD at station Jan06.
amplitude and the duration of the signal for a same-nat-
ured event. An magnitude analysis makes this fact pretty
obvious, this discrepancy in the records also produces
some variation in the magnitude of an event recorded by
several stations. Some examples in the Table 1 below
represent such variations, and allow us to sort out the
stations used for our study into three groups which share
similar behaviors: Jan03 and Jan05; Jan02 and Jan07;
Jan06 and Jan09.
These different behaviors could be explained by some
factors such as the distance between the group of stations
and the event’s epicenter. This situation applies very well
for the contrast among the first group and the others.
Moreover, another factor that may justify that difference
of behavior, mainly between the last two groups, is the
geological setting. Stations Jan02 and Jan07 are localized
nearby a carbonate geology river while stations Jan06
and Jan09 are in a more complex geology region. Never-
theless, the station Jan01 doesn’t fit into either groups.
4. Discussion
Table 1. Comparison of the magnitudes obtained from dif-
With the analysis of each station result, we arrived at a
(s) LogDMD
ferent stations for the same seismic event.
Date_Hour_StationAmp. P (m)ML Dur.
041107_1529_jan011.64E–051.216 50.746 1.7051.747
041107_1529_jan031.02E–051.007 25.966 1.4141.120
041107_1529_jan051.14E–051.059 33.837 1.5291.368
041107_1529_jan065.32E–051.726 61.203 1.7871.922
080208_1529_jan021.38E–051.139 30.993 1.4911.286
080208_1529_jan064.37E–051.640 51.077 1.7081.753
080208_1529_jan074.66E–051.668 25.758 1.4111.113
080208_1529_jan091.22E–042.088 48.924 1.6901.713
Amp. P: P-wave amplituhte m; Dr
eneral equation that enables us to make some estimate
de; ML: Ricr’s localagnitudeur.: Duation of
seismic signal; LogD: Logarithm of duration; MD: Magnitude of local dura-
tion.
g
as to the local magnitude, based on the duration of each
seismic signal for the earthquakes in the Itaracambi-MG
region.

D
M2.1530.072 LogD1.9250.132  (3)
D is the signal’s duration in seconds. It’s worth
tio
[7], we can draw a
co
men-
ning that all the seismometers and registers used were
of the DM24 type (GURALP brand).
Having as a reference the works of
mparison between the Richter’s ML magnitude and the
MD magnitude obtained by Equation (3). In Figure 6
these magnitude’s data have been plotted and indicate
that the adjustments made are sufficiently reliable, the
standard deviation from MD to ML for the seismic activi-
ties of our choice being equal to:

12
2
LD
i137
0.341σ
(4)
From the magnitudes estimated by the Equation (3)
an
can estimate, on the basis of a frequency-
m
 
LogNa bM
LogN0.8260.020 M2.9880.034
Σi MMσ
d from the date on which the events took place, we can
come up with a magnitude × time histogram which can
be used to make an estimate of the region’s seismic oc-
currences.
Also, we
agnitude study, a value for the parameter b using the
Equation (5) according to [9], establishing a correlation
between the number of earthquakes (N) and the duration
of their magnitude (Figure 7). The result obtained for the
parameter b ended up being within the universal range
[2].
 (5)
As next steps of this study, we will estimate the mag-
nitude through the frequency domain [10].
Copyright © 2012 SciRes. IJG
Í. L. DE OLIVEIRA ET AL.
Copyright © 2012 SciRes. IJG
225
Figure 6. Correlation between the ML magnitude and the
MD magnitude.
Figure 7. Logarithm of the number of events (N) × magni-
5. Acknowledgements
ish to thank Ibama (Parque
and the
G.S.F. wishes to thank CNPq-3003529/2010-5.
gical Society of America,
ophysical Research,
. 641-644.
tude (M). Dashed line re presents the Equation (3), b = 0.826
(±0.020).
The authors of this study w
das Cavernas Peruaçu), Mr. Evandro and the city-hall of
Itacarambi-MG for their support in the course of the field
work, Ruan R. Alves and Cesar G. Pavão for several
suggestions that improvement the manuscript. I.L.O.
wishes to thank CNPq for the funding via PIBIC
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