Center for Seismology

Delhi, India

Center for Seismology

Delhi, India
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Babita S.,Center for Seismology | Rastogi B.K.,Institute of Seismological Research
Disaster Advances | Year: 2014

The three-dimensional spatial distribution of relative scattering coefficients is estimated in the Kachchh region, western India, by means of an inversion technique applied to coda wave envelopes. Data used consisted of selected vertical-component, broad band recordings from 438 earthquakes with moment magnitudes Mw ranging from 1.6 to 4.2 and epicentral distances up to 235 km recorded by the Institute of Seismological Research (ISR) seismic network. The results of the inversion analysis yield relative scattering coefficient estimates between ∼1.3 and ∼0.8. Most of the analyzed region reveals small spatial perturbations of the scattering coefficient of the order of ±16%, thus suggesting a uniform distribution of scattering coefficients in the lithosphere beneath Kachchh region for the scale length of the analyzed frequencies between 1 and 2 Hz. This uniformity is broken by the presence of some strong scattering areas distributed in several clusters throughout the region. Moho discontinuity in this region is imaged at average depths between 32 and 42 km. Also it is clear that in the Kachchh region the Moho discontinuity is highly disturbed which may be due to the high velocity body in the lower crust and upper mantle which is consistent with similar studies in the area.

Prajapati S.K.,Center for Seismology | Sunil P.S.,Indian Institute of Geomagnetism | Reddy C.D.,Indian Institute of Geomagnetism
International Association of Geodesy Symposia | Year: 2014

To investigate the transient strain rate of postseismic deformation associated with the highly devastating December 26, 2004 Andaman–Sumatra earthquake (Mw 9.3), a combined analysis have been done using GPS data and Seismic Moment Tensors (SMT) acquired from Andaman–Nicobar–Sumatra regions during 2005–2007. The displacement estimated during postseismic periods 2005–2006 and 2006–2007 with respect to ITRF2008 and Indian Reference Frame, display dominating arc-normal active deformation in the southern part close to epicenter, and arc-parallel deformation towards the northern part of the Andaman– Nicobar–Sumatra Subduction Zone (ANSSZ). The principal strain rates during 2005–2006 periods indicate larger strain accumulation and decreased rate of strain during 2006–2007 with a maximum arc-normal compression on southern part of ANSSZ and a changing trend of arc-parallel extension towards the central and northern part along the ANSSZ. Stress inversion using SMT also indicate compressive horizontal stress in the southern part and extensional stress towards the central and northern part of the study area, and a remarkable agreement with GPS derived strain rate pattern. © Springer-Verlag Berlin Heidelberg 2014.

Verma M.,Center for Seismology | Bansal B.K.,Ministry of Earth science
Geomatics, Natural Hazards and Risk | Year: 2013

This paper provides a brief overview of the progress made towards active fault research in India. An 8 m high scarp running for more than 80 km in the Rann of Kachchh is the classical example of the surface deformation caused by the great earthquake (1819 Kachchh earthquake). Integration of geological/geomorphic and seismological data has led to the identification of 67 active faults of regional scale, 15 in the Himalaya, 17 in the adjoining foredeep with as many as 30 neotectonic faults in the stable Peninsular India. Large-scale trenching programmes coupled with radiometric dates have begun to constraint the recurrence period of earthquakes; of the order of 500-1000 years for great earthquakes in the Himalaya and 10,000 years for earthquakes of >M6 in the Peninsular India. The global positioning system (GPS) data in the stand alone manner have provided the fault parameters and length of rupture for the 2004 Andaman Sumatra earthquakes. Ground penetration radar (GPR) and interferometric synthetic aperture radar (InSAR) techniques have enabled detection of large numbers of new active faults and their geometries. Utilization of modern technologies form the central feature of the major programme launched by the Ministry of Earth Sciences, Government of India to prepare geographic information system (GIS) based active fault maps for the country. © 2013 © 2013 Taylor & Francis.

Srivastava H.N.,Pocket A | Verma M.,Center for Seismology | Bansal B.K.,Ministry of Earth science | Sutar A.K.,Ministry of Earth science
Geomatics, Natural Hazards and Risk | Year: 2015

Contrary to most of the earlier theories that great earthquakes (Mw 8.5 or even larger) may occur anywhere along the Indian plate boundary assuming uniform strain accumulation, this paper proposes two types of gaps with discriminatory characteristics. The new gaps were initially identified from earthquakes of magnitude 6, whose return periods in Himalaya vary between 20 and 30 years and are well within the period of reliable instrumental data of about 100 years. These gaps were then integrated with the largest magnitude event in instrumental era and historical times; information on paleoseismicity, micro-seismicity data, GPS-based geodetic observations and the tectonic features. The regions where great/major earthquakes (Mw 8 or larger) have occurred in the past are classified as seismic gap of category 1, namely Kashmir, west Himachal Pradesh (Kangra), Uttarakhand to Dharachulla, central Nepal to Bihar, Shillong, Arunachal gap including Assam–Tibet–Myanmar syntaxis. On the other hand, the second category of seismic gap includes Jammu–Kishtwar block, east Himachal Pradesh, western Nepal (excluding Dharachulla region) and Sikkim–Bhutan where history of large earthquakes is not available. In these gaps, the largest earthquake magnitude is smaller (7–7.5) and the recurrence interval for earthquakes of same magnitude is larger as compared to category 1 gaps. © 2013, © 2013 Taylor & Francis.

Sharma B.,Center for Seismology | Chingtham P.,Center for Seismology | Sutar A.K.,Center for Seismology | Chopra S.,Center for Seismology | Shukla H.P.,Center for Seismology
Annals of Geophysics | Year: 2015

The attenuation properties of Delhi and surrounding region have been investigated using 62 local earthquakes recorded at nine stations. The frequency dependent quality factors Qα (using P-waves) and Qβ (using Swaves) have been determined using the coda normalization method. Quality factor of coda-waves (Qc) has been estimated using the single backscattering model in the frequency range from 1.5 Hz to 9 Hz. Wennerberg formulation has been used to estimate Qi (intrinsic attenuation parameter) and Qs (scattering attenuation parameter) for the region. The values Qα, Qβ, Qc, Qi and Qs estimated are frequency dependent in the range of 1.5Hz-9Hz. Frequency dependent relations are estimated as Qα= 52f1.03, Qβ= 98f1.07 and Qc= 158f0.97.Qc estimates lie in between the values of Qi and Qs but closer to Qi at all central frequencies. Comparison between Qi and Qs shows that intrinsic absorption is predominant over scattering for Delhi and surrounding region. © 2015 by the Istituto Nazionale di Geofisica e Vulcanologia. All rights reserved.

Srivastava H.N.,Pocket A | Bansal B.K.,Geoscience Div. | Verma M.,Center for Seismology
Journal of the Geological Society of India | Year: 2013

The largest earthquake (Mw 8.4 to 8.6) in Himalaya reported so far occurred in Assam syntaxial bend in 1950. However, some recent studies have suggested for earthquake of magnitude Mw 9 or more in the Himalayan region. In this paper, we present a detailed analysis of seismological data extending back to 1200 AD, and show that earthquake in Himalayan region may not be expected to be as large as those of subduction zones. Also, there appears to be a lateral variation in the earthquake magnitude, being lesser in the western syntaxial bend when compared close to the eastern syntaxial bend. This is attributed to the difference in the plate boundary scenario; dominance of strike-slip and thrusting along the western syntaxis as against thrusting and remnant subduction along the eastern syntaxis. © 2013 Geological Society of India.

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