Source study of two small earthquakes of Delhi, India, and estimation of ground motion from future moderate, local events |
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Authors: | B K Bansal S K Singh R Dharmaraju J F Pacheco M Ordaz R S Dattatrayam G Suresh |
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Institution: | (1) Ministry of Earth Sciences, CGO Complex, Mahasagar Bhavan, Govt. of India, New Delhi, 110003, India;(2) Instituto de Geofísica, UNAM, CU, 04510 México, DF, México;(3) Central Building Research Institute, Roorkee, India;(4) Instituto de Ingeniería, UNAM, CU, 04510 México, DF, México;(5) India Meteorological Department, Lodhi Road, New Delhi, 110003, India |
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Abstract: | We study source characteristics of two small, local earthquakes which occurred in Delhi on 28 April 2001 (Mw3.4) and 18 March
2004 (Mw2.6). Both earthquakes were located in the heart of New Delhi, and were recorded in the epicentral region by digital
accelerographs. The depths of the events are 15 km and 8 km, respectively. First motions and waveform modeling yield a normal-faulting
mechanism with large strike-slip component. The strike of one of the nodal planes roughly agrees with NE–SW orientation of
faults and lineaments mapped in the region. We use the recordings of the 2004 event as empirical Green’s functions to synthesize
expected ground motions in the epicentral region of a Mw5.0 earthquake in Delhi. It is possible that such a local event may
control the hazard in Delhi. Our computations show that a Mw5.0 earthquake would give rise to PGA of ~200 to 450 gal, the
smaller values occurring at hard sites. The estimate of corresponding PGV is ~6 to 15 cm/s. The recommended response spectra,
Sa, 5% damping, for Delhi, which falls in zone IV of the Indian seismic zoning map, may not be conservative enough at soft
sites for a postulated Mw5.0 local earthquake. |
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Keywords: | Delhi seismicity Delhi seismotectonics Delhi seismic hazard Delhi microzonation |
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