Colluvial deposits in northwest Deccan,India: their significance in the interpretation of Late Quaternary history     

Veena U. Joshi  Vishwas S. Kale 《第四纪科学杂志》1997,12(5):391-403

The Deccan Trap region exhibits an erosional landscape over a relatively ancient and stable Deccan shield. The Quaternary history of the area has been reconstructed on the basis of evidence from alluvial deposits occurring along the major rivers. However, recent investigations have revealed that evidence for geo-environmental change during the Quaternary Period is also contained in the colluvial deposits that occur in the foothill zones. The colluvial deposits, ranging in thickness from 1 to 10 m, invariably occupy gently inclined pediment slopes. The sediments are presently deeply dissected by gullies, and the process of colluviation has almost ceased. These deposits are best preserved in the semi-arid parts of the region. Detailed textural, geochemical and stratigraphical studies at four different sites reveal similar input processes, the slight variations being attributed to local environmental factors. Scanning electron microscopy studies of some grains indicate marginal contribution of aeolian processes at the time of deposition. Mesolithic artefacts and a few U/Th dates indicate that the colluviation took place during the Late Quaternary. The properties of the deposits suggest relatively high energy conditions as well as a remarkable variability in the intensity of hillslope processes. These properties are indicative of semi-arid conditions during which the regolith was stripped from devegetated hillslopes and was deposited on the pediments. A variety of evidence indicates that the period of colluviation coincided with arid conditions during the Last Glacial Maximum. The geomorphological and archaeological evidence also indicates that incision by gully systems was initiated during the early Holocene humid phase. The environmental conditions deduced for the study area are similar to those reported for other parts of the intertropical zone. © 1997 John Wiley & Sons, Ltd.  相似文献   

Modeling of the strong ground motion of 25th April 2015 Nepal earthquake using modified semi-empirical technique     

Sohan Lal  A. Joshi  Sandeep  Monu Tomer  Parveen Kumar  Chun-Hsiang Kuo  Che-Min Lin  Kuo-Liang Wen  M. L. Sharma 《Acta Geophysica》2018,66(4):461-477

On 25th April, 2015 a hazardous earthquake of moment magnitude 7.9 occurred in Nepal. Accelerographs were used to record the Nepal earthquake which is installed in the Kumaon region in the Himalayan state of Uttrakhand. The distance of the recorded stations in the Kumaon region from the epicenter of the earthquake is about 420–515 km. Modified semi-empirical technique of modeling finite faults has been used in this paper to simulate strong earthquake at these stations. Source parameters of the Nepal aftershock have been also calculated using the Brune model in the present study which are used in the modeling of the Nepal main shock. The obtained value of the seismic moment and stress drop is 8.26 × 10²⁵ dyn cm and 10.48 bar, respectively, for the aftershock from the Brune model .The simulated earthquake time series were compared with the observed records of the earthquake. The comparison of full waveform and its response spectra has been made to finalize the rupture parameters and its location. The rupture of the earthquake was propagated in the NE–SW direction from the hypocenter with the rupture velocity 3.0 km/s from a distance of 80 km from Kathmandu in NW direction at a depth of 12 km as per compared results.  相似文献   

A deterministic approach for preparation of seismic hazard maps in North East India     

A. Joshi  Kapil Mohan  R. C. Patel 《Natural Hazards》2007,43(1):129-146

A method of seismic zonation based on deterministic modeling of rupture plane is presented in this work. This method is based on the modeling of finite rupture plane along identified lineaments in the region using the semi-empirical technique, of Midorikawa [(1993) Tectonophysics 218:287–295]. The modeling procedure follows ω² scaling law, directivity effects, and other strong motion parameters. The technique of zonation is applied for technoeconomically important NE part of Brahmaputra valley that falls in the seismic gap region of Himalaya. Zonation map prepared for Brahmaputra valley for earthquakes of magnitude M > 6.0 show that approximately 90,000 km² area fall in the highly hazardous zone IV, which covers region that can have peak ground accelerations of order more than 250 cm/s². The zone IV covers the Tezu, Tinsukia, Dibrugarh, Ziro, North Lakhimpur, Itanagar, Sibsagar, Jorhat, Golaghat, Wokha, Senapati, Imphal, and Kohima regions. The Pasighat, Daring, Basar, and Seppa region belong to zone III with peak ground accelerations of the order 200–250 cm/s². The seismic zonation map obtained from deterministic modeling of the rupture is consistent with the historical seismicity map and it has been found that the epicenter of many moderate and major earthquakes fall in the identified zones.  相似文献   

Inversion of seismic intensity data for the determination of three-dimensional attenuation structures in the central gap region of Himalayas     

A. Joshi 《Natural Hazards》2007,43(1):1-22

The central gap region of Himalaya, which lies in the northern part of the Indian subcontinent, is exposed to great seismic hazard. A three-dimensional attenuation structure (Q) of this region is obtained using the intensity data of four earthquakes (M 4.3–7.0) in the central Himalayan gap region and the damped least square inversion scheme. The technique is based on that given by Hashida and Shimazaki (J Phys Earth 32:299–316, 1984). The obtained Q structure explains the spatial distribution of isoseismals of the stronger earthquakes, which occurred in the recent past. The study area covers the Tehri town, which is the locale of one of the biggest earth fill dams of height 260 m. The spatial distribution of Q suggests that the Tehri town area is surrounded by lower Q medium, and hence any large earthquake in Tehri will pose great seismic hazard.  相似文献   

Evolution of geophysical parameters over the Indian Ocean region during contrasting monsoon years of 2002 and 2003 using TRMM/TMI data     

S. H. Rahman  B. Simon  P. C. Joshi 《Theoretical and Applied Climatology》2007,89(3-4):211-227

Summary The evolution of geophysical parameters over Indian Ocean during two contrasting monsoon years 2002 (drought) and 2003 (normal) were studied using TRMM/TMI satellite data. Analysis indicates that there was a lack of total water vapour (TWV) build up over Western Indian Ocean (WIO) during May 2002 (drought) when compared to 2003 (normal). Negative (positive) TWV anomalies were found over the WIO in May 2002 (2003). In 2002, negative SST anomaly of ∼1.5 °C is found over entire WIO when compared to 2003. Anomalously high sea surface wind speed (SWS) anomaly over the South West Indian Ocean (SWIO) and WIO would have resulted in cooling of the sea surface in May 2002 in comparison to 2003. In 2003 the wind speed anomaly over entire WIO and Arabian Sea (AS) was negative, whereas sea surface temperature (SST) anomaly was positive over the same region, which would have resulted in higher moisture availability over these regions. A negative (positive) TWV anomaly over Eastern Arabian Sea (EAS) and positive (negative) anomaly over WIO forms a dipole structure. In the month of June no major difference is seen in all these parameters over the Indian Ocean. In July 2002 the entire WIO and AS was drier by 10–15 mm as compared to 2003. The pentad (5 day) average TWV values shows high (>55 mm) TWV convergence over EAS and Bay of Bengal (BoB) during active periods of 2003, which gives high rainfall over these regions. However, during 2002 although TWV over BoB was >55 mm but it was ∼45–55 mm over EAS during entire July and hence less rainfall. The evaporation has been calculated from the bulk aerodynamic formula using TRMM/TMI geophysical products. It has been seen that the major portion of evaporative moisture flux is coming from southern Indian Ocean (SIO) between 15 and 25° S. Evaporation in June was more over AS and SIO in 2003 when compared to 2002 which may lead to reduce moisture supply in July 2002 and hence less rainfall compared to July 2003.  相似文献   

Population of excited rotational levels of HD and CO in interstellar clouds     

Pushpa Joshi  S. P. Tarafdar 《Astrophysics and Space Science》1975,36(2):291-301

Populations of the rotational levels of vibrational and electronic ground state of interstellar HD and CO have been calculated. Ultraviolet pumping and molecular formation have been found to be very important in the case of HD but not so in CO, the population distribution of which is mainly governed either by 3 K or by collisional excitation. The population inversion has been found to occur in HD but not in CO, the excitation temperatures of which pass through maximum for large ultraviolet flux. The population inversion at large density does not occur in HD, probably due to neglect of multipole collision. The observation of HD and CO in the excited states may be possible for suitable values of density and ultraviolet flux.On leave from Tata Institute of Fundamental Research, Bombay, India.  相似文献   

Intermediate-Term Periodicities in Soft X-ray Flare Index During Solar Cycles 21, 22 and 23     

Bhuwan?JoshiEmail author  Anita?Joshi 《Solar physics》2005,226(1):153-161

We have analyzed the intermediate-term periodicities in soft X-ray flare index (FI_SXR) during solar cycles 21, 22 and 23. Power-spectral analysis of daily FI_SXR reveals a significant period of 161 days in cycle 21 which is absent during cycles 22 and 23. We have found that in cycle 22 periodicities of 74 and 83 days are in operation. A 123-day periodicity has been found to be statistically significant during part of the current solar cycle 23. The existence of these periodicities has been discussed in the light of earlier results.  相似文献   

Analysis of the 9th November 1990 flare     

Anita Joshi  Wahab Uddin 《Journal of Astrophysics and Astronomy》2000,21(3-4):229-232

In this paper we present complete two-dimensional measurements of the observed brightness of the 9th November 1990Hα flare, using a PDS microdensitometer scanner and image processing software MIDAS. The resulting isophotal contour maps, were used to describe morphological-cum-temporal behaviour of the flare and also the kernels of the flare. Correlation of theHα flare with SXR and MW radiations were also studied.  相似文献   

A study of subpulse phase correlation across nulls in PSR B0031−07     

B. C. Joshi  M. Vivekanand 《Monthly notices of the Royal Astronomical Society》2000,316(3):716-720

The correlation of subpulse phases across nulls is investigated in the radio pulsar PSR B0031−07, using 29 849 periods of high-quality data obtained with the Ooty Radio Telescope (ORT) which operates at 327 MHz. Assuming that the turn-off and turn-on subpulse phases (the phase of the subpulse in the last period before the null and that in the first period after the null, respectively) are independent random variables, the expected distribution of their difference (i.e. the total drift) is inconsistent with the observed distribution for null transitions within the same drift mode; this implies a correlation of subpulse phase across nulls. However, this correlation decreases with null duration for both the dominant drift modes. Substantial drifting occurs during short nulls (one to four periods); the drift rate during the short nulls appears to be constant for a class A transition, whereas it decreases with null duration for class B transitions. These results, together with the reported behaviour of PSR B1944+17 and PSR B0809+74, seem to imply different time-scales for phase correlation in different pulsars.  相似文献   

Long-term historic changes in climatic variables of Betwa Basin,India   总被引：2，自引：1，他引：1  

Shakti Suryavanshi  Ashish Pandey  Umesh Chandra Chaube  Nitin Joshi 《Theoretical and Applied Climatology》2014,117(3-4):403-418

In this study, trend analyses of historic past climatic variables were investigated for the Betwa basin located in Central India. In the serially independent climatic variables, Mann–Kendall test (MK test) was applied to the original sample data. However, in the serially correlated series, pre-whitening is used before employing the MK test. The long-term trend analysis showed several of the meteorological stations to exhibit a decreasing trend in annual and seasonal precipitation in the study area. Seasonal and yearly numbers of rainy days are decreased. However, onset of effective monsoon (except for Shivpuri and Tikamgarh stations) did not show any trend during the study period. For maximum temperature, five out of 12 stations showed a decreasing trend in monsoon season whereas almost all other stations showed an increasing trend in winter and no trend in summer season. For minimum temperature, only two stations of the basin showed a decreasing trend in monsoon and all other stations exhibited a significant increase in winter and summer season. The increase of winter temperature may adversely affect the growth of Rabi crop (wheat and mustard) in the study area. Potential evopotranspiration (PET) did not show any trend in monsoon, except for Jalaun and Jhansi stations, showing decreasing trends. Raisen and Vidisha stations showed an increasing trend in winter only, and the trend for other stations were random in nature. In summer, five out of 12 stations showed an increasing trend in PET. Results of this study can be employed in preparation of water resources development and management plan in the Betwa Basin.  相似文献