Institute of Seismological Research

Ghandinagar, India

Institute of Seismological Research

Ghandinagar, India
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Kothyari G.C.,Institute of Seismological Research | Luirei K.,Wadia Institute of Himalayan Geology
Geomorphology | Year: 2016

The present study has been carried out with special emphasis on the aggradational landforms to explain the spatial and temporal variability in phases of aggradation/incision in response to tectonic activity during the late Quaternary in the Saryu River valley in central Kumaun Himalaya. The valley has preserved cut-and-fill terraces with thick alluvial cover, debris flow terraces, and bedrock strath terraces that provide signatures of tectonic activity and climate. Morphostratigraphy of the terraces reveals that the oldest landforms preserved south of the Main Central Thrust, the fluvial modified debris flow terraces, were developed between 30 and 45 ka. The major phase of valley fill is dated between 14 and 22 ka. The youngest phase of aggradation is dated at early and mid-Holocene (9-3 ka). Following this, several phases of accelerated incision/erosion owing to an increase in uplift rate occurred, as evident from the strath terraces. Seven major phases of bedrock incision/uplift have been estimated during 44 ka (3.34 mm/year), 35 ka (1.84 mm/year), 15 ka (0.91 mm/year), 14 ka (0.83 mm/year), 9 ka (1.75 mm/year), 7 ka (5.38 mm/year), and around 3 ka (4.4 mm/year) from the strath terraces near major thrusts. We postulate that between 9 and 3 ka the terrain witnessed relatively enhanced surface uplift (2-5 mm/year). © 2016 Elsevier B.V.

Chopra S.,Institute of Seismological Research | Choudhury P.,Institute of Seismological Research
Soil Dynamics and Earthquake Engineering | Year: 2011

In this study, the effect of ground geology on the acceleration response spectra is studied at 32 sites in Gujarat, India. The sites are grouped into Proterozoic, Mesozoic, Tertiary and Quaternary. The normalized acceleration response spectra at 5% damping of 407 strong ground motions (horizontal and vertical components) recorded at these sites varying in magnitude from 3.0 to 5.7 are determined. The study shows that the shape of the acceleration response spectra is influenced by the regional geology and local site conditions. The peak of maximum horizontal spectral amplification is between 0.03 and 0.05. s in Proterozoic formations, 0.06 and 0.10. s in Mesozoic formations, 0.06 and 0.08. s in Tertiary and 0.12. s in Quaternary formations. The maximum vertical spectral acceleration is at 0.025. s in Proterozoic, 0.07. s in Mesozoic, 0.05. s in Tertiary and 0.10. s in Quaternary formations. The average acceleration amplification factor in all the geological formations is between 2.5 and 3.0 both in horizontal and vertical components. It has been observed that acceleration response spectra at sites having same geological formations are also influenced by local site conditions. The study shows that the acceleration response spectrum in the current Indian code applicable for the entire country underestimates the seismic forces at hard-rock sites and overestimates at soft-soil sites. Using recorded strong motion data with Mw ranging from 3.5 to 5.7, an attenuation relationship is developed at six periods to predict geometric mean of horizontal spectral amplitudes for rock and soil sites. The spectral amplitudes predicted with the attenuation relationship match well with the observed one within statistical limits for hypocentral distances less than 200 km. © 2011 Elsevier Ltd.

Chopra S.,Institute of Seismological Research | Kumar D.,Kurukshetra University | Rastogi B.K.,Institute of Seismological Research
Pure and Applied Geophysics | Year: 2011

The local earthquake waveforms recorded on broadband seismograph network of Institute of Seismological Research in Gujarat, India have been analyzed to understand the attenuation of high frequency (2-25 Hz) P and S waves in the region. The frequency dependent relationships for quality factors for P (QP) and S (QS) waves have been obtained using the spectral ratio method for three regions namely, Kachchh, Saurashtra and Mainland Gujarat. The earthquakes recorded at nine stations of Kachchh, five stations of Saurashtra and one station in mainland Gujarat have been used for this analysis. The estimated relations for average QP and QS are: QP = (105 ± 2) f0.82 ± 0.01, QS = (74 ± 2) f1.06 ± 0.01 for Kachchh region; QP = (148 ± 2) f0.92 ± 0.01, QS = (149 ± 14) f1.43 ± 0.05 for Saurashtra region and QP = (163 ± 7) f0.77 ± 0.03, QS = (118 ± 34) f0.65 ± 0.14 for mainland Gujarat region. The low Q (<200) and high exponent of f (>0.5) as obtained from present analysis indicate the predominant seismic activities in the region. The lowest Q values obtained for the Kachchh region implies that the area is relatively more attenuative and heterogeneous than other two regions. A comparison between QS estimated in this study and coda Q (Qc) previously reported by others for Kachchh region shows that QC>QS for the frequency range of interest showing the enrichment of coda waves and the importance of scattering attenuation to the attenuation of S waves in the Kachchh region infested with faults and fractures. The QS/QP ratio is found to be less than 1 for Kachchh and Mainland Gujarat regions and close to unity for Saurashtra region. This reflects the difference in the geological composition of rocks in the regions. The frequency dependent relations developed in this study could be used for the estimation of earthquake source parameters as well as for simulating the strong earthquake ground motions in the region. © 2010 Birkhäuser/Springer Basel AG.

Phartiyal B.,University of Lucknow | Singh R.,University of Lucknow | Kothyari G.C.,Institute of Seismological Research
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2015

Records from the Tangtse Valley in the Trans-Himalaya reveal depositional history since 48ka, with fluvial aggradation followed by incision, lacustrine sediment fill, and later incision. Varied sedimentary architecture with fluvial episodes intervened by lacustrine pulses, flood events, colluvial and glacial activity are preserved. The valley is located west of the Pangong Tso/Bangong Co, one of the largest lakes in Tibet which has served as a spillway, flooding and damming the entire Tangtse Valley, resulting in the formation of a lake. Today Pangong Tso consists of five basins separated by shallow sills and is fed by snow melt. Documentation based on 14C and OSL chronologies of the sediment sections throughout the valley reveals evidence of a sixth basin of Pangong Tso toward west, occupying the present day Tangtse Valley between 9.6-5.1ka. This event coincides with periods of high lake levels in Tibet, China as well as intensified monsoon periods over the Indian subcontinent. A fluvial regime around 48ka and 30-21ka with comparatively arid conditions and dry phases interspersed by flooding is documented. The valley has been incised to depths of 40-50m in the upper part and to 130m in the lower part. The incision rate ranges from 0.3 to 1.2mmyr-1 in the upper part and reaches as high as 10.8mmyr-1 in the lower valley. Much of the incision took place between 22 and 9.6ka although repeated sediment fill-incision cycles in the valley from 30-22ka, 22-9.6ka, 9.6-5.1ka, 5.1ka, and even to present time were observed. © 2014 Elsevier B.V.

Manglik A.,CSIR - Central Electrochemical Research Institute | Pavan Kumar G.,CSIR - Central Electrochemical Research Institute | Pavan Kumar G.,Institute of Seismological Research | Thiagarajan S.,CSIR - Central Electrochemical Research Institute
Tectonophysics | Year: 2013

The tectonics of seismically active Sikkim Himalaya, as inferred by numerous seismological studies, is distinct from the conventional thrust tectonics proposed for the Himalayan collision belt. Here, focal mechanisms of several moderate magnitude earthquakes and composite fault plane solutions of microearthquakes have revealed strike-slip motion along faults transverse to the northward convergence direction of the Indian plate. In the present study, we analyze broadband magnetotelluric data of 12 sites located along an approximately N-S profile cutting across major geological sub-domains of Sikkim to test whether magnetotelluric strikes also support such transverse tectonic nature of the region. We have performed strike analysis of the data by two decomposition approaches as well as by phase tensor method. The study has revealed local variations in the strike directions within the region consistent with the geological and tectonic setup and the presence of transverse tectonic features in the region of Main Central Thrust Zone (MCTZ) where major axis of phase ellipses align in NNW-SSE to NW-SE direction. This trend coincides with the one obtained by microseismic data recorded after the September 18, 2011 earthquake (Mw 6.9). Magnetotelluric strike analysis thus supports the presence of NNW-to-NW trending transverse tectonic zone in MCTZ. © 2013 Elsevier B.V.

Rastogi B.K.,Institute of Seismological Research
Proceedings of the Indian National Science Academy | Year: 2016

Recent seismological research in India can be mainly grouped into study of 1) seismogenesis and seismotectonics of the three regions viz., Himalaya, Andaman-Nicobar subduction zone and the Stable Continental region (SCR); 2) Strong motion study and 3) earthquake prediction. Last few years have witnessed significant change in monitoring of earthquakes through about hundred broadband seismographs in National Network and many more in clusters whose data are brought online to two centers at National Centre for Seismology, Delhi and INCOIS, Hyderabad. Extensive research on reservoir induced earthquakes has culminated into "Deep Crustal Drilling" (DCD) in the Koyna-Warna region down to focal depth to understand the nucleation and generation process of earthquakes. © 2016 Printed in India.

Singh A.P.,Institute of Seismological Research
Soil Dynamics and Earthquake Engineering | Year: 2015

In western India during the Bhuj earthquake (Mw 7.6) on January 26, 2001, the Anjar City at ~30km southwest of Bhuj experienced three types of damage scenario: severely damaged, less damaged and non-damaged. Similar damage patterns were also observed for the 1819 (Mw 7.8) and the 1956 (Mw 6.0) earthquakes. Microtremor array measurements were conducted in and around the Anjar city to examine the strength of soil structures and damage pattern. Significant differences are observed in frequencies and amplitudes in horizontal-to-vertical spectral ratio (HVSR) using microtremor measurements. The severely- damaged site shows two peak amplitudes: 2.8 at 1.2Hz; and 4.0 at 8.0Hz. The less-damaged site also shows two amplitudes: 2.5 and 2.1 at 1.4Hz; and 2.0Hz, respectively. The non-damaged site, on the other hand, shows that the HVSR curves become almost flatter. Similar results for three types of damage scenario based on analyses of earthquake records are also observed for the study area. The microtremor array measurements has revealed shear wave velocity Vs≥400m/s at 18m depth in the non-damaged, at 40m in the less-damaged and at 60m depth in the severely-damaged sites. The site amplitudes and the Vs values show a good correlation with the soil characteristics and damage pattern, suggesting that strength of soil layers at varying depths is a dictating factor for the estimate of the earthquake risk evaluation of the area under study. © 2015 Elsevier Ltd.

Kothyari G.C.,Institute of Seismological Research
Zeitschrift fur Geomorphologie | Year: 2015

Morphometric analysis in association with fluvial landform study has been used to ascertain the tectonic instability/stability in Pindar and Saryu River valleys of the central Kumaun Himalaya. To assess tectonic activities in the area, geomorphic indices namely, stream-gradient index (SL), drainage basin asymmetry (AF), topographic asymmetric factor (T), Valley-Floor Height Ratio (Vf) and Elongation Ratio (Re) have been studied. The results of morphometric analysis are in consistent with the field evidences. The study suggests that the terrain close to Main Central Thrust (MCT) and the North Almora Thrust (NAT) is under - going deformation, which is attributed to the regional compression. More specifically, using the valley morphology and longitudinal river profile, the Pindar and Saryu River valleys are divided into three and two broad tectonomorphic zones, respectively. In the Pindar River valley, zone-1 is bounded by the MCT1 to MCT3, Dwali-Phurkiya Fault (DPF), Dulam-Khati Fault (DKF), zone-2 by Askot Thrust (AT) and Baijnath Thrust (BjT) whereas zone-3 is demarcated by Narayanbagar Thrust (NT) and Alaknanda Fault (AF). The two zones in Saryu River valley are bounded by MCT 2 to 3, DKF and AT, NAT. The study suggests that the above-mentioned structures exert significant influence in the evolution of fluvial landform, thus advocates tectonically active nature of the terrain. These structures are considered to be tectonically active. Integrating the morphometry and the geomorphic expressions of tectonic instability suggests that in Pindar River zone-1 and zone-3 are more tectonically active compared to zone-3, whereas in Saryu River valley, zone-2 shows enhanced deformation. © 2014 Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart, Germany.

Phartiyal B.,University of Lucknow | Kothyari G.C.,Institute of Seismological Research
Zeitschrift fur Geomorphologie | Year: 2012

The Spiti river basin in North West Indian Himalaya (31-33° E; 77-79 °S), is tectonically unstable, exhibits a complex topography, landscape relief and varied Quaternary sedimentation. The major geomorphic landforms viz., alluvial terraces, strath terraces, alluvial fans, debris cone, fluvio-lacustrine deposits, scree and talus cone are present throughout the valley. An attempt has been made by using the geomorphometry approach to access the area in terms of its neotectonic instability, as this basin feeds the river Sutlej. We tried to see the Spiti and the Parachu basin of draining into Sutlej valley, which have been in news several times in the last decade causing floods downstream, due to the outburst of glacial lakes and the formation of temporary lakes during the sliding events, even by the slight disturbance in the monsoon pattern and tectonic activity. Thus the landforms were mapped and assessed in the valley to elucidate spatio-temporal scale dependencies of surface processes active in this region. The Spiti river (constituting of Spiti and Parachu basins) was examined using geomorphic field methods (Spiti basin) and OSL dating. The Quaternary saw ubiquitous mass movements and catastrophic landslides which transported material from steep slopes to valley bottoms and were responsible for the formation of lakes (preserved as thick sequences of fine sediment), while the outburst floods redistributed sediment downvalley affecting life and property downstream. The morphometric approach such as Basin Asymmetry (AF), Topographic Symmetric Factor (T), Stream length Gradient Index (GI) Hydauralic Sinuosity Index (HSI), Topographic sinuosity Index (TSI) and Standard Sinuosity Index (SSI) have helped in understanding tectonic and climatic perturbation. Our observations point towards a tectonically active region with enormous piles of loose, unconsolidated sediment cover which could be disastrous during the slight shift of the climatic and tectonic forces operating in this area. © 2011 Gebr. Borntraeger Verlagsbuchhandlung Stuttgart Germany.

Aggarwal S.K.,Institute of Seismological Research | Lovallo M.,ARPAB | Khan P.K.,Indian School of Mines | Rastogi B.K.,Institute of Seismological Research | Telesca L.,National Research Council Italy
Physica A: Statistical Mechanics and its Applications | Year: 2015

The sequence of magnitudes of the earthquakes occurred in Kachchh area (Gujarat, Western India) from 2003 to 2012, has been analysed by using the multifractal detrended fluctuation analysis. The complete and the aftershock-depleted catalogues with minimum magnitude M3 were investigated. Both seismic catalogues show multifractal characteristics. The aftershock-depleted catalogue is more multifractal and also more persistent than the whole catalogue; this indicates that aftershock magnitudes contribute to increase the homogeneity and the randomness of the magnitude sequence of the whole seismicity. The singularity spectrum of the whole catalogue, however, is more left-skewed than that of the aftershock-depleted one, indicating a stronger dependence of the multifractality on the large magnitude fluctuations. © 2015 Elsevier B.V. All rights reserved.

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