HAZARIKA, D and Baruah, S and Gogoi, N K
(2009)
Attenuation of coda waves in the Northeastern Region
of India.
J Seismology, 13.
pp. 141-160.
Abstract
Coda wave attenuation quality factor
Qc is estimated in the northeastern region of India
using 45 local earthquakes recorded by regional
seismic network. The quality factor Qc was estimated
using the single backscattering model modified
by Sato (J Phys Earth 25:27–41, 1977), in
the frequency range 1–18 Hz. The attenuation and
frequency dependence for different paths and the
correlation of the results with geotectonics of the
region are described in this paper. A total of 3,890
Qc measurements covering 187 varying paths are
made for different lapse time window of 20, 30, 40,
50, 60, 70, 80, and 90 s in coda wave. The magnitudes
of the analyzed events range from 1.2 to 3.9
and focal depths range between 7 and 38 km. The
source–receiver distances of the selected events
range between 16 and 270 km. For 30-s duration,
the mean values of the estimated Qc vary from
50 ± 12 (at 1 Hz) to 2,078 ± 211(at 18 Hz) for the Arunachal Himalaya, 49 ± 14 (at 1 Hz) to
2,466 ± 197 (at 18 Hz) for the Indo-Burman, and
45 ± 13 (at 1 Hz) to 2,069 ± 198 (at 18 Hz) for
Shillong group of earthquakes. It is observed
that Qc increases with frequency portraying
an average attenuation relation Qc = 52.315 ±
1.07 f (1.32±0.036) for the region. Moreover, the pattern
of Qc−1 with frequency is analogous to the
estimates obtained in other tectonic areas in the
world, except with the observation that the Qc−1
is much higher at 1Hz for the northeastern region.
The Qc−1 is about 10−1.8 at 1 Hz and decreases to
about 10−3.6 at 18 Hz indicating clear frequency
dependence. Pertaining to the spatial distribution
of Qc values, Mikir Hills and western part
of Shillong Plateau are characterized by lower
attenuation.
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