Evaluating the seismic hazard to the National Capital (Delhi) Region,India, from moderate earthquakes using simulated accelerograms |
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| Authors: | Dinesh Kumar Irene Sarkar V Sriram S S Teotia |
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| Institution: | (1) Department of Geophysics, Kurukshetra University, Kurukshetra, 136 119, Haryana, India;(2) School of Basic and Applied Sciences, Shobhit University, Meerut, Uttar Pradesh, India;(3) Wadia Institute of Himalayan Geology, G.M.S. Road, Dehradun, 248 001, India |
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| Abstract: | The National Capital Region (NCR) of India is exposed to high seismic hazard and risk due to a great earthquake in the central
seismic gap of Himalaya and/or due to moderate-size earthquake within NCR. The high population density, rapid growth of infrastructure,
and old engineering structures in the region make it more vulnerable to the human as well as economic loss due to moderate-size
earthquakes also. The evaluation of seismic hazard is the first step to prepare a proper mitigation plan for the region. The
aim of this paper is to evaluate the seismic hazard and risk due to moderate-size earthquakes in the vicinity of NCR. For
this purpose, a suit of accelerograms have been generated from hypothetical moderate-size earthquakes (M 5.5 and 6.0) in the region. A basic fault-plane solution is assumed for this purpose. The ranges of the different parameters
like depth of focus and stress drop values have been used in order to examine the effect of these parameters on hazard. The
accelerograms have been synthesized using two basic velocity models, one representing a hard site and the other a site with
a significant low-velocity cover. These two velocity models represent the ridge area and trans-Yamuna river area in the NCR.
The decay of peak ground acceleration (pga) values with distance is fast in trans-Yamuna region (with low-velocity surface
layer of 100 m) as compared to that of ridge area (with low-velocity surface layer of 1 m). Also, the decay of pga becomes
slower if we increase the depth of focus from 10 to 20 km. The response spectra (5% damping) of the synthetic accelerograms
for the three periods T = 0.4s, 0.75s, and 1.25s have been estimated and presented in the form of decay curves. The amplifications as a function
of epicentral distance and stress drop have also been estimated. We note that the amplifications in 100-m layer case do not
occur uniformly at all the distances, rather it is dependent on the angle of incidence of energy into the layers. The pga
values are generally amplified by more than twice with increase in stress drop from 100 to 400 bars. The seismic exposure
of the population in Delhi city has been presented. The results presented in this study may serve as an important input in
the planning of mitigation and disaster management programs in the National Capital Region. |
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