The deadliest stable continental region earthquake occurred near Bhuj on 26 January 2001     

B.K. Rastogi  H.K. Gupta  Prantik Mandal  H.V.S. Satyanarayana  M. Kousalya  R. Raghavan  Richa Jain  A.N.S. Sarma  N. Kumar  C. Satyamurty 《Journal of Seismology》2001,5(4):609-615

A large destructive earthquake occurred on 26 January 2001 in the region of Kutch, Gujarat, in Western India, with magnitude Mw 7.7. The earthquake caused very heavy damage and a large number of casualties with more than 20,000 deaths. A preliminary study of ground deformation, damage pattern and aftershock distribution is presented.  相似文献   

Aftershock Activity and Frequency-dependent Low Coda Qc in the Epicentral Region of the 1999 Chamoli Earthquake of Mw 6.4     

P. Mandal  S. Padhy  B. K. Rastogi  H. V. S. Satyanarayana  M. Kousalya  R. Vijayraghavan  A. Srinivasan 《Pure and Applied Geophysics》2001,158(9-10):1719-1735

— On 28 March, 1999 (19:05:10.09, UT) a significant earthquake of M _w 6.4 occurred in the Garhwal Himalaya (30.555°N, 79.424°E). One hundred and ten well-recorded aftershocks show a WNW-ESE trending northeasterly dipping seismic zone extending from a depth of 2 to 20?km. As the main shock hypocenter occurred at the northern end of this seismic zone and aftershocks extended updip, it is inferred that the main-shock rupture nucleated on the detachment plane at a depth of 15?km and then propagated updip along a NE-dipping thrust plane. Further, the epicentral distribution of aftershocks defines a marked concentration near a zone where main central thrust (MCT) takes a significant turn towards the north, which might be acting as an asperity in response to the NNE compression due to the underthrusting of Himalayan orogenic process prevalent in the entire region. Presence of high seismicity including five earthquakes of magnitude exceeding 6 and twelve earthquakes of magnitude exceeding 5 in the 20th century is presumed to have caused a higher level of shallow crustal heterogeneity in the Garhwal Himalaya, a site lying in the central gap zone of the Himalayan frontal arc. Attenuation property of the medium around the epicentral area of the 1999 Chamoli earthquake, covering a circular area of 61,500?km² with a radius of 140?km, is studied by estimating the coda Q _c from 48 local earthquakes of magnitudes varying from 2.5–4.8. These earthquakes were recorded at nine 24-bit REFTEK digital stations; two of which were equipped with three-component CMG40T broadband seismometers and others with three-component L4-3D short-period seismometers. The estimated Q _o values at different stations suggest on average a low value of the order of (30?±?0.8), indicating an attenuating crust beneath the entire region. The frequency-dependent relation indicates a relatively low Q _c at lower frequencies (1–3?Hz) that can be attributed to the loss of energy due to scattering on heterogeneities and/or the presence of faults and cracks. The large Q _c at higher frequencies may be related to the propagation of backscattered body waves through deeper parts of the lithosphere where less heterogeneities are expected. An important observation is that the region north of MCT (more rigid highly metamorphosed crystalline rocks) is less attenuative in comparison to the region south of MCT (less rigid slightly metamorphosed rocks (sedimentary wedge)). The acceleration decays to 50% at 20?km distance and to 7% at 100?km. Hence, even 1g acceleration at the source may not cause significant damage beyond 100?km in this region.  相似文献   

Determination of soil impedance functions from vibration-test response of a circular foundation     

M. G. Srinivasan  C. A. Kot  B. J. Hsieh 《Soil Dynamics and Earthquake Engineering》1991,10(4)

The paper presents the results of the determination from vibration tests of impedance functions for a concrete basemat of a one-quarter scale model of a nuclear power-plant containment building. The tests were designed to excite all rigid-body modes of the foundation. In addition to the impedance functions for all the rigid-body degrees of freedom, natural frequencies and damping for the fundamental modes were estimated. Comparison of the test-determined modal characteristics with corresponding analytical ones based on the Lysmer analog shows that though the latter gives natural-frequency estimates of the right order of magnitude, it does not give acceptable estimates of the damping coefficient. Analytical impedance functions based on a model of a rigid-plate on an elastic half-space were found to have the sam trend as the test-determined ones at lower frequencies, but not at higher frequencies. The utility of test data for verification of analysis is discussed.  相似文献   

Noble gases in six ordinary chondrites: comparison of exposure ages from noble gases with ²⁶Al ages     

B. Srinivasan 《Geochimica et cosmochimica acta》1977,41(7):977-983

Noble gases were redetermined in six ordinary chondrites in order to clarify some discrepancies between cosmic-ray exposure ages from noble gas isotopes and ²⁶Al activity. Generally, samples used for noble-gas analyses were from the same specimen which earlier had been used for ²⁶Al determinations in this laboratory. The high ²¹Ne ages (> 3 × 10⁶ y) for Dimmitt, Menow and Pierceville are consistent with ²⁶A1 activity at saturation level. Variations in both ²¹Ne_c age and ²⁶Al activity, in earlier measurements on Dimmitt, were due to “shielding”; very low noble-gas ages in earlier analyses on Menow and Pierceville were due to mis-labelling of samples. Earlier observation of very low noble-gas ages for Seres, which is inconsistent with its saturation activity of ²⁶Al, is confirmed. Ladder Creek yields consistent ages both from noble gases and ²⁶Al. Malotas contains a substantial excess of ²¹Ne, as revealed by a higher ²¹Ne age, compared to its ²⁶Al age; the excess ²¹Ne is probably due to “pre-irradiation”. Isotopic compositions for trapped Kr and Xe in these chondrites, excepting Seres, are very similar to compositions determined earlier for ordinary chondrites. The Xe in Seres is enriched in light isotopes and is similar to solar Xe.  相似文献   

Geomorphic interpretation of the Landsat images in Tamilnadu     

V. Srinivasan  V. Gopal 《Journal of the Indian Society of Remote Sensing》1982,10(2):75-76

Landsat imagery were used to interpret the geomorphic festures in the northern part of Tamilnadu between latitudes 11° and 12°30′ N and longitudes 77° and 80° E. Different geomorphic regions were identified with the aid of ground truths. These geomorphic regions, in general, are controlled by the underlying rock types. As the different geomorphic regions have different signatures in the Landsat images, the geomorphic interpretation, which helps to bring out the regional geology is possible with the aid of ground truths.  相似文献   

Interpretation of an apollo space photo for small scale soil mapping in respect of an area in bihar     

G. Krishnamurti  T. R. Srinivasan 《Journal of the Indian Society of Remote Sensing》1973,1(1-2):75-81

A section of an Apollo space photo relating to the Magadh area of Bihar state was monoscopically interpreted resulting in six delineations based upon tone and texture variations. Small scale aerial photographs were used for the preparation of soil map of a part of the area using a systematic air photointerpretation procedure; this served as a basis for defining the soil composition of four out of the six space photo analytical units. In respect of the remaining two units-soil information was obtained by reference to an existing small seale soil map of Bihar State. The data thus obtained have been used to prepare a small scale soil map of the selected section of the Apollo space photo. The soil map of the part of the space photo area that is based on support ph: to-interpretation has been found to have the quality and accuracy expected of very small scale soil maps.  相似文献   

NOBLE GASES IN THE UNIQUE CHONDRITE,KAKANGARI     

B. Srinivasan  Edward Anders 《Meteoritics & planetary science》1977,12(4):417-424

The Kakangari chondrite has a cosmic-ray exposure age of 5.4 m.y. and a K-Ar age near 4 g.y. Its high cosmogenic ³He/²¹Ne ratio of 7.5 indicates a small preatmospheric mass. The He and Ne are largely of solar-wind origin, presumably implanted during exposure in the regolith of its parent body. The heavy gases Ar, Kr, Xe are largely of planetary origin. Taken together, the low ¹²⁹Xe/¹³²Xe (1.07), low ³⁶Ar/¹³²Xe (225), and high ¹³²Xe content (45 × 10^?10 cc STP/g) are more similar to the values for unequilibrated ordinary chondrites or even C1, C2 chondrites than to enstatite chondrites, and suggest that Kakangari has the same gas-bearing mineral assemblage as the former, in spite of its high degree of reduction (Fa_4.9).  相似文献   

Weathering impact on the colour of building stones of the ‘Gateway of India’ monument     

L. B. Tiwari  C. J. Jahagirdar  V. D. Deshpande  R. Srinivasan  G. Parthasarathy 《Environmental Geology》2005,48(6):788-794

To understand the effect of monsoon and marine environment on the colour of building stones of the ‘Gateway of India’ monument, 133 samples from different areas were assessed. Colour changes were evaluated using Microflash 200d colour spectrophotometer over a period of 1 year. The alteration in the stones effecting the colour change was studied by petrographic thin section, which shows that the colour change is associated with weathering of the feldspars.  相似文献   

Superposed folding in the Honakere arm of the Chitradurga-Karighatta schist belt in the Dharwar tectonic province,southern India,and its bearing on the Sargur-Dharwar relation     

K. Naha  A. Rai Choudhuri  V. Ranjan  R. Srinivasan 《Journal of Earth System Science》1995,104(3):327-347

The supracrustal enclave within the Peninsular Gneiss in the Honakere arm of the Chitradurga-Karighatta belt comprises tremolite-chlorite schists within which occur two bands of quartzite coalescing east of Jakkanahalli(12°39′N; 76°41′E), with an amphibolite band in the core. Very tight to isoclinal mesoscopic folds on compositional bands cut across in the hinge zones by an axial planar schistosity, and the nearly orthogonal relation between compositional bands and this schistosity at the termination of the tremolite-chlorite schist band near Javanahalli, points to the presence of a hinge of a large-scale, isoclinal early fold (F₁). That the map pattern, with an NNE-plunging upright antiform and a complementary synform of macroscopic scale, traces folds 'er generation (F ₂),is proved by the varying attitude of both compositional bands (S₀) and axial pranar schistosity (S ₁), which are effectively parallel in a major part of the area. A crenulation cleavage (S ₂) has developed parallel to the axial planes of theF ₂ folds at places. TheF ₂ folds range usually from open to rarely isoclinal style, with theF ₁ andF ₂ axes nearly parallel. Evidence of type 3 fold interference is also provided by the map pattern of a quartzite band in the Borikoppalu area to the north, coupled with younging directions from current bedding andS ₀ -S ₁ inter-relation. Although statistically theF ₁ andF ₂ linear structures have the same orientation, detailed studies of outcrops and hand specimens indicate that the two may make as high an angle as 90°. Usually, in these instances, theF ₁ lineations are unreliable around theF ₂ axes, implying that theF ₂ folding was by flexural slip. In zones with very tight to almost isoclinalF ₂ folding, however, buckling attendant with flattening has caused a spread of theF ₁ lineations almost in a plane. Initial divergence in orientation of theF ₁ lineations due to extreme flattening duringF ₁ folding has also resulted in a variation in the angle between theF ₁ andF ₂lineations in some instances. Upright later folding (F₃) with nearly E-W strike of axial planes has led to warps on schistosity, plunge reversals of theF ₁ andF ₂ axes, and increase in the angle between theF ₁ andF ₂ lineations at some places. Large-scale mapping in the Borikoppalu sector, where the supposed Sargur rocks with ENE ‘trend’ abut against the N-‘trending’ rocks of the Dharwar Supergroup, shows a continuity of rock formations and structures across the hinge of a large-scaleF ₂ fold. This observation renders the notion, that there is an angular unconformity here between the rocks of the Sargur Group and the Dharwar Supergroup, untenable.  相似文献   

The nature of the basement in the Archaean Dharwar craton of southern India and the age of the Peninsular Gneiss     

K Naha  R Srinivasan  K Gopalan  GVC Pantulu  M V Subba Rao  A B Vrevsky  Ye S Bogomolov 《Journal of Earth System Science》1993,102(4):547-565

The Archaean Peninsular Gneiss of southern India is considered by a number of workers to be the basement upon which the Dharwar supracrustal rocks were deposited. However, the Peninsular Gneiss in its present state is a composite gneiss formed by synkinematic migmatization during successive episodes of folding (DhF₁, DhF_1a and DhF₂) that affected the Dharwar supracrustal rocks. An even earlier phase of migmatization and deformation (DhF_*) is evident from relict fabrics in small enclaves of gneissic tonalites and amphibolites within the Peninsular Gneiss. We consider these enclaves to represent the original basement for the Dharwar supracrustal rocks. Tonalitic pebbles in conglomerates of the Dharwar Supergroup confirm the inference that the supracrustal rocks were deposited on a gneissic basement. Whole rock Rb-Sr ages of gneisses showing only the DhF₁ structures fall in the range of 3100–3200 Ma. Where the later deformation (DhF₂) has been associated with considerable recrystallization, the Rb-Sr ages are between 2500 Ma and 2700 Ma. Significantly, a new Rb-Sr analysis of tonalitic gneiss pebbles in the Kaldurga conglomerate of the Dharwar sequence is consistent with an age of ～2500 Ma and not that of 3300 Ma reported earlier by Venkatasubramanian and Narayanaswamy (1974). Pb-Pb ages based on direct evaporation of detrital zircon grains from the metasedimentary rocks of the Dharwar sequence fall into two groups, 3300–3100 Ma, and 2800–3000 Ma. Stratigraphic, structural, textural and geochronologic data, therefore, indicate that the Peninsular Gneiss of the Dharwar craton evolved over a protracted period of time ranging from > 3300 Ma to 2500 Ma.  相似文献