Rb−Sr and Ar−Ar systematics of Malani volcanic rocks of southwest Rajasthan: Evidence for a younger post-crystallization thermal event     

S S Rathore  T R Venkatesan  R K Srivastava 《Journal of Earth System Science》1996,105(2):131-141

A new Rb−Sr age of 779±10 Ma has been obtained for a suite of andesite-daciterhyolite from the Malani Igneous Province of southwestern Rajasthan, dated earlier at 745±10 Ma by Crawford and Compston (1970). The associated basalts may be slightly younger than the felsic volcanics and have a mantle source. The felsic volcanics on the other hand were most probably derived by fractional crystallization of a crustal magma (Srivastavaet al 1989a, b).⁴⁰Ar−³⁹Ar systematics of three samples viz., a basalt, a dacite and a rhyolite show disturbed age spectra indicating a thermal event around 500–550 Ma ago. This secondary thermal event is quite wide-spread and possibly related to the Pan-African thermo-tectonic episode observed in the Himalayas and south India.  相似文献   

Heavy metal distribution and environmental status of Doon Valley soils, Outer Himalaya, India   总被引：1，自引：0，他引：1  

K. K. Purohit  P. K. Mukherjee  P. P. Khanna  N. K. Saini  M. S. Rathi 《Environmental Geology》2001,40(6):716-724

 Doon Valley is surrounded by two major river systems (Ganga and Yamuna) on either side, with a water divide passing nearly across the centre of the valley, and is sandwiched between two mountain ranges in the fragile ecological systems of the Himalayan foothills. In total 398 soil samples were collected from the valley in a grid pattern (∼1 sample per 2 km²) and investigated for their heavy metal (Cr, Cu, Ni, Pb and Zn) abundances that are environmentally sensitive. Comparison of the heavy metal abundances with the contamination threshold values (CTV) revealed that most of these elemental abundances in Doon Valley soils fall well within the range of the uncontaminated to slightly contaminated category. In the case of Cr and Ni, a sizeable number of samples exceeded the CTV (250 and 100 mg kg^–1 respectively) with an overall background value of 109 and 52 mg kg^–1 respectively. Sites of high Cr and Ni mostly occur in the Ganga Catchment (GC) sector that includes even relatively undisturbed forestland. The source of this contamination is attributed to geological factors which indicate contribution from the mafic volcanics of the Lesser Himalaya. This is also consistent with the distribution pattern of Mn and Fe, though their abundance levels are not alarming. The background concentration of Pb is low (22 mg kg^–1) in Doon Valley soils; however, signs of gradual Pb contamination are palpable in and around the centre of the Dehra Dun city and along the highways. Aluminium normalized heavy metal ratios were found to exhibit narrow variability in the case of Cu, Ni and Cr and had good correlation with Al, indicating their affinity and association with the clay minerals. On the other hand, Pb and Zn seem to be associated with non-silicate sources. Received: 7 January 2000 · Accepted: 30 July 2000  相似文献   

1-D Theoretical Modeling for Site Effect Estimations in Thessaloniki: Comparison with Observations     

P. Triantafyllidis  P. M. Hatzidimitriou  P. Suhadolc 《Pure and Applied Geophysics》2001,158(12):2333-2347

—?We apply an algorithm based on the modal summation method to theoretically estimate the site effect at selected locations underlain by different geological formations within the city of Thessaloniki (Greece). Complete strong motion synthetics are constructed for all components of motion at each site, for a maximum frequency of 10?Hz. The anelastic, local 1-D velocity models are based on cross-hole data. Four point sources with different azimuths and distances from the city are used to compute the input signals. The theoretical amplification is estimated through spectral ratios of accelerograms obtained by the local 1-D over those obtained by the regional 1-D velocity model. The results from the numerical modeling are compared with those derived from experimental techniques, such as of Standard Spectral Ratio and Horizontal-to-Vertical Spectral Ratio, which had been applied to acceleration data recorded at the same sites. The comparison demonstrates that the theoretical amplifications based on known and simple subsurface geology can be used as a first-order estimate, while for cases of more complex geometries the use of at least 2-D modeling in site effects estimation is mandatory.  相似文献   

Forest change detection in Kalarani round, Vadodara, Gujarat— a Remote Sensing and GIS approach     

Jessica P Karia  M C Porwal  P S Roy  G Sandhya 《Journal of the Indian Society of Remote Sensing》2001,29(3):129-135

Studies on spatial distribution of the different forests during 1970 to 1999 using integrated remote sensing and GIS techniques reveals that area under forests in the Kalarani Round, is progressively reducing with the time. In 1970 forest area was found to be 22.75 sq km. in 1989 it was 15.34 sq km and in 1999 it was only 12.93 sq km. Thus. there is considerable loss in the tree cover from 1989 to 1999. Jhanpa and Kalarani R.F. are the example of this. Ground surveys indicate that the majority of the loss is caused by heavy grazing pressure there by decreasing regeneration of vegetation. If suitable measures are not taken. whole area may be converted into wasteland in due course of time. Another reason for the forest loss, could be land encroachments by villagers for their overwhelming needs. Karali R.F. is not much disturbed apart from the plantation raised in the foothills. Outside the reserve forest boundary, the change was observed due to construction of Narmada Sagar canal.  相似文献   

Vegetation type discrimination on Landsat TM data in heterogeneous forested landscape of Western Ghats—Accuracy evaluation from large scale aerial photo maps     

M C Porwal  P S Roy 《Journal of the Indian Society of Remote Sensing》1992,20(1):21-33

In the present study, forest type classification using Landsat TM False Colour Composite (FCC) bands 2, 3, 4 has been evaluated for mapping highly heterogeneous forest environment of Western Ghats (Kerala). Visual interpretation of Landsat TM FCC has been carried out to identify bioclimatic vegetation types. For accuracy estimation maps prepared from 1∶15,000 scale black-and-white aerial photographs have been used as ground check data. For comparison aerial photomap classes have been aggregated to match with Landsat-TM-derived map. The classification accuracy of ten major bioclimatic and landcover types was estimated using systematic sampling procedure. The overall classification accuracy of the forest types for the study area was 88.33%.  相似文献   

Simultaneous inversion of the aftershock data of the 1993 Killari earthquake in Peninsular India and its seismotectonic implications     

S. Mukhopadhyay  J. R. Kayal  K. N. Khattri  B. K. Pradhan 《Journal of Earth System Science》2002,111(1):1-15

The aftershock sequence of the September 30th, 1993 Killari earthquake in the Latur district of Maharashtra state, India, recorded by 41 temporary seismograph stations are used for estimating 3-D velocity structure in the epicentral area. The local earthquake tomography (LET) method of Thurber (1983) is used. About 1500P and 1200S wave travel-times are inverted. TheP andS wave velocities as well asV _P/V_Sratio vary more rapidly in the vertical as well as in the horizontal directions in the source region compared to the adjacent areas. The main shock hypocentre is located at the junction of a high velocity and a low velocity zone, representing a fault zone at 6–7 km depth. The estimated average errors ofP velocity andV _P/V_Sratio are ±0.07 km/s and ±0.016, respectively. The best resolution ofP and S-wave velocities is obtained in the aftershock zone. The 3-D velocity structure and precise locations of the aftershocks suggest a ‘stationary concept’ of the Killari earthquake sequence.  相似文献   

Investigation for planimetric accuracy of airborne synthetic aperture radar     

R P Kala  M Nazim 《Journal of the Indian Society of Remote Sensing》1993,21(1):45-48

The airborne SAR images were tested for geometric accuracy in order to assess the suitability of present airborne radar systems for topographic mapping. Images were transformed to terrain coordinate system using 2-D conformal, affine and polynomial transformations. Standard error in positional discrepancies at check points show that the geometric fidelity of present airborne SAR system is compatible with planimetric mapping requirements at 1∶50,000 and smaller scale.  相似文献   

Mass movement studies in Kosi catchment,mepal — A semi quantitative approach using aerial photographs     

S. K. Subramanian  D. P. Rao 《Journal of the Indian Society of Remote Sensing》1986,14(1):61-65

An area of about 5000 sq. km. in the upper parts of river basin of Sun Kosi falling in Nepal has been studied using medium and small scale aerial photographs of two different dates. The temporal variations in relation to mass movements that occur in the study area have been demarcated. The areas which have undergone increased erosion by slope failure and gully erosion over a period of 22 years are evaluated. An attempt has been made to quantify the increase in area of mass movement taking the advantage of three dimensional model of terrain as seen in the aerial photos.  相似文献   

Hydrogeology of Talwandi Sabo Tehsil,Bathinda District (Punjab): A remote sensing approach     

A Thomas  V K Verma  A Sood  P K Litoria  P K Sharma  K V Ravindran 《Journal of the Indian Society of Remote Sensing》1995,23(2):47-56

Studies on water resources and hydrogeology of an area have become much easier with the help of Remote Sensing Technology. As an attempt to evaluate hydrogeology and ground water conditions of the tehsil Talwandi Sabo, Bathinda district, a hydromorphogeological map of the area was prepared through visual interpretation of satellite imagery. The study shows that the study area, a part of the Indo-Gangetic alluvial plain, is occupied by a large number of sand-dune complexes deposited by the ancient Satluj River while traversing the area during the past. Later on reworking of sand-dunes by aeolian action and their physical removal for agricultural purposes resulted in the present landscape of a plain land with sanddune complexes. Unconsolidated Quaternary alluvial sediments consisting of fine to medium-grained sand with admixture of kankar and some clay constitute the aquifer system of the area. Studies show that ground water occurs under both confined and unconfined conditions with water table at shallow depths. But the quality of the ground water is poor to marginal in most of the area except in the vicinity of main canal (Kotla Branch) where water seepage from canals has made the ground water good in quality.  相似文献   

A Study of Source Parameters, Site Amplification Functions and Average Effective Shear Wave Quality Factor Qseff from Analysis of Accelerograms of the 1999 Chamoli Earthquake, Himalaya     

Dinesh Kumar  V. Sri Ram  K. N. Khattri 《Pure and Applied Geophysics》2006,163(7):1369-1398

The accelerograms of the 1999 Chamoli earthquake and nine of its aftershocks, which occurred in Uttaranchal Himalaya, have been analyzed to investigate their source parameters, the site amplification functions and the average effective shear-wave quality factor Q_seff in the region. The fault plane solution of the main shock is obtained using the spectral amplitudes of SH waves (approximated by transverse components of accelerograms) of the high-energy packets observed in the accelerograms of the main shock. It is found to be comparable with the reported solutions in other studies. Similarly the other source parameters (viz., seismic moment = (5.03±1.7) × 10²⁵ dyne-cm, stress drop = 65 bars, source duration = 5.2 s and moment magnitude = 6.4) estimated for the main shock are consistent with the values obtained in other studies. The stress drops estimated for the aftershocks vary from 23 bars to 153 bars and the seismic moment from 1.4 × 10²³ dyne-cm to 2.9 × 10²³ dyne-cm. The average estimated values of the effective shear-wave quality factor Q_seff vary from 655±359 in the Uttaranchal sector of Himalaya and 1475±130 in the Delhi region. In general, the Q_seff value increases with an increase in the epicentral distance reflecting the penetration of the waves into deeper layers of the crust as the epicentral distance of the observation point increases. These values of Q_seff indicate that in general the curst is at low temperatures that will promote brittle behavior and conditions for episodic failure as compared to creep, under the accumulated strains from plate collision at the Himalaya plate boundary. The site amplification characteristics at sites have been identified from the frequency bands of significant amplification observed in the spectral ratios of the horizontal to the vertical component records. The decay of peak ground acceleration (PGA) values with distance has been investigated using the empirical regression curves vis-à-vis the site amplification factors.  相似文献