Guest editorial: Paleotsunami     

Arun Kumar  Ioan Nistor 《Natural Hazards》2012,63(1):1-3

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Estimation of heavy rainfall during cyclonic storms from microwave observations using nonlinear approach over Indian Ocean     

Anoop Kumar Mishra 《Natural Hazards》2012,63(2):673-683

In this study, an effort has been made to study heavy rainfall events during cyclonic storms over Indian Ocean. This estimate is based on microwave observations from tropical rainfall measuring mission (TRMM) Microwave Imager (TMI). Regional scattering index (SI) developed for Indian region based on measurements at 19-, 21- and 85-GHz brightness temperature and polarization corrected temperature (PCT) at 85?GHz have been utilized in this study. These PCT and SI are collocated against Precipitation Radar (PR) onboard TRMM to establish a relationship between rainfall rate, PCT and SI. The retrieval technique using both linear and nonlinear regressions has been developed utilizing SI, PCT and the combination of SI and PCT. The results have been compared with the observations from PR. It was found that a nonlinear algorithm using combination of SI and PCT is more accurate than linear algorithm or nonlinear algorithm using either SI or PCT. Statistical comparison with PR exhibits the correlation coefficients (CC) of 0.68, 0.66 and 0.70, and root mean square error (RMSE) of 1.78, 1.96 and 1.68?mm/h from the observations of SI, PCT and combination of SI and PCT respectively using linear regressions. When nonlinear regression is used, the CC of 0.73, 0.71, 0.79 and RMSE of 1.64, 1.95, 1.54?mm/h are observed from the observations of SI, PCT and combination of SI and PCT, respectively. The error statistics for high rain events (above 10?mm/h) shows the CC of 0.58, 0.59, 0.60 and RMSE of 5.07, 5.47, 5.03?mm/h from the observations of SI, PCT and combination of SI and PCT, respectively, using linear regression, and on the other hand, use of nonlinear regression yields the CC of 0.66, 0.64, 0.71 and RMSE of 4.68, 5.78 and 4.02?mm/h from the observations of SI, PCT and combined SI and PCT, respectively.  相似文献   

Numerical simulation of cloud burst event on August 05, 2010, over Leh using WRF mesoscale model   总被引：1，自引：1，他引：0  

M. Sravana Kumar  M. S. Shekhar  S. S. V. S. Rama Krishna  M. R. Bhutiyani  A. Ganju 《Natural Hazards》2012,62(3):1261-1271

Localized deep cumulus convective clouds have a capability of giving enormous amount of rainfall over a limited horizontal area, within a short span of time. Such types of extreme rainfall events are most common over the high elevated areas of Northern India during the Southwest monsoon season which causes widespread damage to the property and lives. Therefore, it is necessary to predict such extreme events accurately to avoid damage associated with them. The numerical mesoscale model Weather Research and Forecasting has been used to simulate the cloud burst event of Leh on August 05, 2010, so as to capture the main characteristics of the various parameters associated with this localized mesoscale phenomenon. The model has been integrated with four nested domains keeping Leh and its adjoining area as center. Two cloud microphysics parameterization schemes namely WSM3 and WSM6 have been used for the sensitivity experiments and results have been analyzed to examine the performance of both the schemes in capturing such extreme localized heavy rainfall events. Results show that the WSM6 microphysics was able to simulate the precipitation near to the observation. WSM3 microphysics simulated the location of the circulation near to the observation. In addition, the results also show that the maximum magnitudes of meridional and vertical wind as simulated with WSM3 microphysics are 12 and 4 m/s, respectively.  相似文献   

Theoretical Equations of Vertical and Radial Consolidation by Equating Degrees of Consolidation by Settlement Analysis and Dissipation of Pore Pressure     

Sudhir Kumar Tewatia  Asuri Sridharan  Mangu Singh  Sunanda Rath 《Geotechnical and Geological Engineering》2012,30(4):1037-1043

Degree of consolidation, U, is defined in two ways: (1) by settlement analysis and (2) by dissipation of pore pressure. Equations of vertical and radial consolidations are derived by equating the above two U. The new equations are compared with the existing equations of vertical and radial consolidations. It is shown that new equation of radial consolidation is exactly same as Barron’s equation of equal strain radial consolidation while in case of vertical consolidation it is similar to later part of Terzaghi’s equation of vertical consolidation. A few possible reasons and advantages of comparison are given. The theory of rapid loading methods is based on the equality of these two degrees of consolidations. It is concluded that in rapid loading methods the next load increment can be applied at any time in radial consolidation once the effects of initial compression are over. However, in vertical consolidation it can be applied only after 60% consolidation.  相似文献   

Groundwater simulation studies of parts of Western Yamuna Canal Command area, Haryana for planning sustainable development     

S. K. Maanjhu  K. J. Anandha Kumar 《Journal of the Geological Society of India》2012,80(4):539-545

A single layer mathematical model was developed to simulate the hydrogeological condition and groundwater flow in an area of about 2536 Sq km, which forms part of the WYC Command area. The model was run both for the steady state and for the transient state. The model was then successfully calibrated. The calibration results were recorded qualitatively and quantitatively. The results of the calibrated model were analyzed. Two Scenarios developed alonwith six scenarios created earlier, in another modeling study, were analyzed to find out a sustainable solution for optimal utilization of surface and ground water. The two Scenarios developed show that a viable solution will be reduction in pumping and regulated surface water supply. This will ameliorate water logging in the nearby areas. The reduction in pumping and thereby, reduction of return flow recharging groundwater can be achieved by improving water use efficiency and modifying/changing cropping pattern. These strategies can be successfully implemented, through mass awareness programmes, involving the farmers, who have to implement the programme, along with all the other stake holders. Ultimately reduction of groundwater pumping can be achieved through strict groundwater regulation. Direct recharge by way of seepage through canal can be reduced by lining the unlined canals and proper repair and maintenance of the already lined canals. But this has to be tested through a pilot project vis-a-vis economic viability of this lining, as seepage may be indirectly helping groundwater recharge in areas without water logging. Further to increase the availability of surface water and augment recharge of groundwater, the surface run off from the precipitation, can be utilized in various ways to reduce to decline of groundwater level.  相似文献   

MnNCKFMASH phase relations in cordierite-orthopyroxene migmatitic gneisses, southern india: implications for low-pressure crustal melting under granulite-facies   总被引：1，自引：0，他引：1  

C. Sreejith  G. R. Ravindra Kumar 《Journal of the Geological Society of India》2012,80(5):613-627

Cordierite-orthopyroxene migmatitic gneisses exposed in Achankovil unit of the Kerala Khondalite Belt, southern India show evidences of melting, melt extraction and in-situ crystallization of melt under granulite-facies conditions. The sequential mineral assemblages garnet + biotite + orthopyroxene + plagioclase + quartz (± melt) in the mesosomes and garnet + biotite + orthopyroxene + cordierite + plagioclase + K-feldspar + quartz + melt in the melanosomes makes the Achankovil cordierite-orthopyroxene migmatitic gneisses a good example of anatectic rocks, where substantial melt fractions remained in-situ during decompression and cooling. Therefore, the rocks provide an opportunity to investigate deep crustal processes and record of rheological (thermal and mechanical) reequilibration prevailed during the final stages of orogeny. The significance of cordierite formation and its possible relationship with melt formation are investigated applying theoretical calculations in the MnO-Na₂O-CaO-K₂O-FeO-MgO-Al₂O₃-SiO₂-H₂O (MnNCKFMASH) system. Results of numerical modelling of the mineral assemblages in pressure-temperature-composition (P-T-X) pseudosections using Perple_X infer that the sequence of reactions involving formation of cordierite-orthopyroxene-melt assemblage is consistent with an isothermal decompression (with a pressure drop of >1.5 kbars) at high temperatures (>800 °C), forming leucosomes. Biotite dehydration melting reactions, occurring above 4.5 kbars constrain prograde arm of the P-T trajectory and is interpreted as a product of crustal thickening, which was followed by rapid decompression. The final stage of exhumation is characterized by rehydration of cordierites in the melanosome by melt-solid interactions at exceptionally low-pressure (??3.2 kbars) conditions. The high-temperature isothermal decompression inferred from the mineral reactions and P-T-X pseudosections constitute a clockwise P-T path for the exhumation of the lower crust. This clockwise P-T path is consistent with the common tectonic model accepted for the genesis of granulite-facies migmatites during crustal thickening and later unroofing, accompanied with arc-continent collision. Our conclusions indicate low-P metamorphism and anatexis can be traced to convergent setting, where melt buoyancy considerably decreases density of the lithosphere and modifies rheology leading to rapid exhumation of the lower crust. Therefore, the crustal evolution in the Kerala Khondalite Belt is correlated with two stage processes: (i) thickening of the crust in relation to a continental-arc setting, followed by (ii) exhumation along a high-temperature stable geotherm with sufficient pressure release associated with syn- to post-convergence transpression and transtension.  相似文献   

Water problems of Bengaluru — the fastest growing city of India     

Amar Kumar Majumdar 《Journal of the Geological Society of India》2012,79(4):424-424

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Structural controls on coal fire distributions — Remote sensing based investigation in the Raniganj coalfield,West Bengal     

Arindam Guha  K. Vinod Kumar 《Journal of the Geological Society of India》2012,79(5):467-475

Coal fires are serious problem in Raniganj coalfield as it is the case for some of the other coalfields of India like Jharia coalfield. Earlier efforts were made to map the coal fires of this coal-field based on satellite observation. But the restricted distribution of major coal fires in the particular portion of the coalfield makes the basis for finding the geological control if responsible for coal fire distribution. In present study, night time thermal data of ASTER (Advance spaceborne thermal emission and reflection radiometer) is used to map the latest distribution (December, 2006) of coal fires in the Raniganj coalfield. Coal fire map shows that most significant zone affected by fire is at the north-western portion of the coalfield; where NE-trending open cast mines are affected by fire. This fire zone is associated with high grade coal of the Barakar Formation. Coal fires are also mapped in open cast pits of Jambad-Mangalpur area occurring over rocks of the Raniganj Formation. By integrating geological map and satellite-derived coal fire map of Raniganj coal field, it is observed that the coal fires detected by remote sensing study are spatially associated with intraformational faults. These faults may have played significant role in supplying oxygen to these coal-fires and allowing them to propagate down the depth along the trends of the faults.  相似文献   

Spectroscopic study of rocks of Hutti-Maski schist belt,Karnataka     

Arindam Guha  Debashish Chakraborty  A. B. Ekka  Kaushik Pramanik  K. Vinod Kumar  S. Chatterjee  S. Subramanium  D. Ananth Rao 《Journal of the Geological Society of India》2012,79(4):335-344

Recent developments in sensor technology have given an onset for studying the earth surface features based on the detailed spectroscopic observation of different rocks and minerals. The spectroscopic profiles of the rocks are always quite different than their constituent minerals however, the spectral profile of a rock can be broadly reconstituted from the spectral profile of each constituent minerals. Interpretation of rock spectra using the spectra of constituent minerals based on relative spectral matching can bring out interesting information on the rock. Present study is an effort toward this and it highlights how visible-near infrared-shortwave-infrared (VNIR-SWIR) rock spectroscopy acts as an useful tool for understanding the rock-mineralogy in indirect and rapid way. It has also been observed that spectral signatures of rocks; studied in present case, are related to spectral signatures of constituent minerals although absorption features of constituent mineral in the rock are also modified by the other minerals juxtaposed in the rock fabric. However, each rock of the study area has their significant absorption features, but many of the absorption signatures are closely spaced, as altered rock has significant absorption at 2305 nm whereas amphibolite has its important absorption signature in 2385 nm and metabasalt has its significant absorption at 2342 nm. Therefore spectral measurement of high spectral resolution with appreciable signal to noise ratio (SNR) only can detect rocks from each other based on the absorption signatures mentioned above (each of which is 10 to 20 nm apart from the other) and therefore spectroscopy of rock is an innovative technique to map rocks and minerals based on the spectral signatures.  相似文献   

2-D velocity structure in Kerala-Konkan basin using traveltime inversion of seismic data     

Praveen Kumar Singh  Kalachand Sain 《Journal of the Geological Society of India》2012,79(1):53-60

The existence of gas-hydrates in marine sediments increases the seismic velocity, whereas even a small amount of underlying free-gas reduces the velocity considerably. The change in velocities against the background (without gas-hydrates and free-gas) velocity can be used for identification and assessment of gas-hydrates. Traveltime inversion of identifiable reflections from large offset multi channel seismic (MCS) experiment is an effective method to derive the 2-D velocity structure in an area. We apply this method along a seismic line in the Kerala-Konkan (KK) offshore basin for delineating the gas-hydrates and free-gas bearing sediments across a bottom simulating reflector (BSR). The result reveals a four layer 2-D shallow velocity model with the topmost sedimentary layer having velocity of 1,680–1,740 m/s and thickness of 140–190 m. The velocity of the second layer of uniform thickness (110 m) varies from 1,890 to 1,950 m/s. The third layer, exhibiting higher velocity of 2,100–2,180 m/s, is interpreted as the gas-hydrates bearing sediment, the thickness of which is estimated as 100 to 150 m. The underlying sedimentary layer shows a reduction in seismic velocity between 1,620 to 1,720 m/s. This low-velocity layer with 160–200 m thickness may be due to the presence of free-gas below the gas-hydrates layer.  相似文献