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Ground-Motion Scaling in the Kachchh Basin, India, Deduced from
Language
English
Status
Published
JCR Journal
JCR Journal
Title of the book
Issue/vol(year)
5/94 (2004)
Publisher
SSA
Pages (printed)
1658–1669
Issued date
2004
Keywords
Abstract
We studied the excitation, propagation, and site effects in the Kachchh
basin of India by using ground-motion recordings from a temporary seismograph
network deployed to study aftershocks of the Mw 7.6 Bhuj earthquake of 26 January
2001. The Kachchh basin has been proposed as a useful analog region for studying
hazard in other earthquake-prone but slowly deforming regions, such as the central
United States. The earthquakes we studied ranged in size from about M 2 to M 5.2,
and travel paths ranged from a few kilometers to about a hundred kilometers. There
was a broad range of focal depths among the aftershocks, so the data were divided
into two overlapping subsets to test the sensitivity of the derived propagation and
source parameters to focal depth. Parameters we constrained include the source excitation
terms (related to stress drop), a frequency-dependent attenuation operator, a
geometric spreading function, and an operator to account for site effects. Our results
indicate that seismic-wave attenuation in Kachchh crust is very low, similar to other
continental intraplate areas such as central and eastern North America. We also estimated
seismic moments and stress drops for the earthquakes by fitting singlecorner-
frequency source-model spectra to the observed spectra, corrected for propagation
by using our derived parameters. Stress drops were found to scale with
seismic moment and to be rather high overall. By using a stochastic point-source
model to estimate mainshock ground motions, we found that the distance decay of
expected peak ground motions, assuming a stress drop of 15–20 MPa, compare well
with the scant observations for the Bhuj earthquake. Ground-motion predictions for
Kachchh, based on Bhuj aftershock data, support the idea that the region may have
similar hazard to proposed analog areas in North America.
basin of India by using ground-motion recordings from a temporary seismograph
network deployed to study aftershocks of the Mw 7.6 Bhuj earthquake of 26 January
2001. The Kachchh basin has been proposed as a useful analog region for studying
hazard in other earthquake-prone but slowly deforming regions, such as the central
United States. The earthquakes we studied ranged in size from about M 2 to M 5.2,
and travel paths ranged from a few kilometers to about a hundred kilometers. There
was a broad range of focal depths among the aftershocks, so the data were divided
into two overlapping subsets to test the sensitivity of the derived propagation and
source parameters to focal depth. Parameters we constrained include the source excitation
terms (related to stress drop), a frequency-dependent attenuation operator, a
geometric spreading function, and an operator to account for site effects. Our results
indicate that seismic-wave attenuation in Kachchh crust is very low, similar to other
continental intraplate areas such as central and eastern North America. We also estimated
seismic moments and stress drops for the earthquakes by fitting singlecorner-
frequency source-model spectra to the observed spectra, corrected for propagation
by using our derived parameters. Stress drops were found to scale with
seismic moment and to be rather high overall. By using a stochastic point-source
model to estimate mainshock ground motions, we found that the distance decay of
expected peak ground motions, assuming a stress drop of 15–20 MPa, compare well
with the scant observations for the Bhuj earthquake. Ground-motion predictions for
Kachchh, based on Bhuj aftershock data, support the idea that the region may have
similar hazard to proposed analog areas in North America.
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