SITARAM , M V D and BORAH , P K
(2007)
Signal Durations and local Richter magnitudes in northeast india: An empirical approach.
J GEOLOGICAL SOCIETY OF INDIA, 70 (2).
pp. 323-338.
Abstract
Twenty four analog seismic stations are operated by the
Regional Research Laboratory (Jorhat), National Geophysical
Research Institute (Hyderabad) and by the India
Meteorological Department (IMD) in the Northeastern region
(NER) of India. 8000 seismograms of 1992 shallow (5-30km)
earthquakes recorded by these stations during the period from
January 1985 to December 1999, have been used to establish
relationships between signal durations and the local Richter
magnitudes (ML). In order to obtain the empirical relations for
the determination of duration magnitudes (MD), signal duration
estimates have been fitted using regression analysis to models
of the form Model-I: MD = C0 + C1 Log10 (S.D) + C2 Δ + C3 h
Model-II: MD = C0 + C1 Log10 (S.D) + C2 Δ + C3 h + C4 [Log10
(S.D)]2, where S.D is the signal duration in seconds, Δ
epicentral distance in degree and h focal depth in km. The
models yielded duration magnitudes at each of the 24 stations
having standard deviations as low as 0.07. For these stations,
station factors are obtained by finding the average of the
deviations of network magnitude (i.e. mean estimate of station
magnitudes for each earthquake, denoted by MD A) from
station magnitudes (MD) for the earthquake events in NER.
Over - and under - estimations of station magnitudes with
respect to ML are also determined for each station. It has been
observed that the estimates of MD (A) scatter up to about
0.8units with respect to ML for both the models. Application of
these factors reduced scatter down to ± 0.25 units for both the
models. © Geol. Soc. India.
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