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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