Sensitivity analysis of seismic hazard for the northwestern portion of the state of Gujarat, India   总被引：1，自引：0，他引：1  

Mark D. Petersen  B.K. Rastogi  Eugene S. Schweig  Stephen C. Harmsen  Joan S. Gomberg 《Tectonophysics》2004,390(1-4):105-115

We test the sensitivity of seismic hazard to three fault source models for the northwestern portion of Gujarat, India. The models incorporate different characteristic earthquake magnitudes on three faults with individual recurrence intervals of either 800 or 1600 years. These recurrence intervals imply that large earthquakes occur on one of these faults every 266–533 years, similar to the rate of historic large earthquakes in this region during the past two centuries and for earthquakes in intraplate environments like the New Madrid region in the central United States. If one assumes a recurrence interval of 800 years for large earthquakes on each of three local faults, the peak ground accelerations (PGA; horizontal) and 1-Hz spectral acceleration ground motions (5% damping) are greater than 1 g over a broad region for a 2% probability of exceedance in 50 years' hazard level. These probabilistic PGAs at this hazard level are similar to median deterministic ground motions. The PGAs for 10% in 50 years' hazard level are considerably lower, generally ranging between 0.2 g and 0.7 g across northwestern Gujarat. Ground motions calculated from our models that consider fault interevent times of 800 years are considerably higher than other published models even though they imply similar recurrence intervals. These higher ground motions are mainly caused by the application of intraplate attenuation relations, which account for less severe attenuation of seismic waves when compared to the crustal interplate relations used in these previous studies. For sites in Bhuj and Ahmedabad, magnitude (M) 7 3/4 earthquakes contribute most to the PGA and the 0.2- and 1-s spectral acceleration ground motion maps at the two considered hazard levels.  相似文献   

An intense SFE and SSC event in geomagnetic H, Y and Z fields at the Indian chain of observatories     

R. G. Rastogi  D. R. K. Rao  S. Alex  B. M. Pathan  T. S. Sastry 《Annales Geophysicae》1997,15(10):1301-1308

Changes in the three components of geomagnetic field are reported at the chain of ten geomagnetic observatories in India during an intense solar crochet that occurred at 1311 h 75° EMT on 15 June 1991 and the subsequent sudden commencement (SSC) of geomagnetic storm at 1518h on 17 June 1991. The solar flare effects (SFE) registered on the magnetograms appear to be an augmentation of the ionospheric current system existing at the start time of the flare. An equatorial enhancement in AH due to SFE is observed to be similar in nature to the latitudinal variation of SQ (H) at low latitude. AF registered the largest effect at 3.6° dip latitude at the fringe region of the electrojet. AZ had positive amplitudes at the equatorial stations and negative at stations north of Hyderabad. The SSC amplitude in the H component is fairly constant with latitude, whereas the Z component again showed larger positive excursions at stations within the electrojet belt. These results are discussed in terms of possible currents of internal and external origin. The changes in the Y field strongly support the idea that meridional current at an equatorial electrojet station flows in the ionospheric dynamo, E.Presently at: School of Physics, University of New South Wales, Sydney, Australia  相似文献   

Midday reversal of equatorial ionospheric electric field     

R. G. Rastogi 《Annales Geophysicae》1997,15(10):1309-1315

A comparative study of the geomagnetic and ionospheric data at equatorial and low-latitude stations in India over the 20 year period 1956–1975 is described. The reversal of the electric field in the ionosphere over the magnetic equator during the midday hours indicated by the disappearance of the equatorial sporadic E region echoes on the ionograms is a rare phenomenon occurring on about 1% of time. Most of these events are associated with geomagnetically active periods. By comparing the simultaneous geomagnetic H field at Kodaikanal and at Alibag during the geomagnetic storms it is shown that ring current decreases are observed at both stations. However, an additional westward electric field is superimposed in the ionosphere during the main phase of the storm which can be strong enough to temporarily reverse the normally eastward electric field in the dayside ionosphere. It is suggested that these electric fields associated with the V × Bz electric fields originate at the magnetopause due to the interaction of the solar wind and the interplanetary magnetic field.  相似文献   

Coastal boulders as evidences of high-energy marine events from Diu Island,west coast of India: storm or palaeotsunami?     

Prizomwala  S. P.  Gandhi  Drasti  Ukey  Vishal M.  Bhatt  Nilesh  Rastogi  B. K. 《Natural Hazards》2015,75(2):1187-1203

Natural Hazards - The coastal segment of Diu Island from west coast of India has been studied for its boulder deposits. The dimensions, morphology and characteristics of these boulders were studied...  相似文献   

Infrared and Raman spectra of lunar samples from Apollo 11, 12 and 14     

Clive H. Perry  D. K. Agrawal  E. Anastassakis  R. P. Lowndes  A. Rastogi  N. E. Tornberg 《Earth, Moon, and Planets》1972,4(3-4):315-336

We report the room temperature infrared reflectance spectra of several lunar surface rocks in the form of polished slices or butt ends. The spectra were obtained over the frequency range 20-2000 cm^–1 throughout the mid and far infrared (5-500µ) region of the electromagnetic spectrum where the fundamental internal and lattice vibrational modes of all minerals and rocks occur.Some fines samples were examined as pressed pellets and their reflectivities compared with the bulk samples. Several terrestrial minerals and rocks were also investigated. Kramers-Kronig analyses of these reflectance spectra were undertaken and the dispersion of the dielectric response ( and ) and the optical constants (n andk) have been determined over this frequency range. The low frequency and high frequency (infrared) dielectric constants were also calculated from the reflectance data.Raman light scattering measurements were made on all the samples supplied from the first three Apollo missions. Large background scattering proved to be the greatest experimental problem. Successful spectra in nearly all cases were obtained from small crystalline inclusions imbedded in the main ground mass. Some crystalline bulk rocks containing many very fine inclusions gave identifiable spectra and at least three different types were obtained.Supported by NASA Grant NGR 22-011-069 and by a Northeastern University Grant for Basic Research.  相似文献   

An Objective Analysis of Support Vector Machine Based Classification for Remote Sensing     

Thomas Oommen  Debasmita Misra  Navin K. C. Twarakavi  Anupma Prakash  Bhaskar Sahoo  Sukumar Bandopadhyay 《Mathematical Geosciences》2008,40(4):409-424

Accurate thematic classification is one of the most commonly desired outputs from remote sensing images. Recent research efforts to improve the reliability and accuracy of image classification have led to the introduction of the Support Vector Classification (SVC) scheme. SVC is a new generation of supervised learning method based on the principle of statistical learning theory, which is designed to decrease uncertainty in the model structure and the fitness of data. We have presented a comparative analysis of SVC with the Maximum Likelihood Classification (MLC) method, which is the most popular conventional supervised classification technique. SVC is an optimization technique in which the classification accuracy heavily relies on identifying the optimal parameters. Using a case study, we verify a method to obtain these optimal parameters such that SVC can be applied efficiently. We use multispectral and hyperspectral images to develop thematic classes of known lithologic units in order to compare the classification accuracy of both the methods. We have varied the training to testing data proportions to assess the relative robustness and the optimal training sample requirement of both the methods to achieve comparable levels of accuracy. The results of our study illustrated that SVC improved the classification accuracy, was robust and did not suffer from dimensionality issues such as the Hughes Effect.  相似文献   

Understanding plot‐scale hydrology of Lesser Himalayan watershed—A field study and HYDRUS‐2D modelling approach          下载免费PDF全文

Aliva Nanda  Sumit Sen  Vijay Jirwan  Anupma Sharma  Vikram Kumar 《水文研究》2018,32(9):1254-1266

Soil moisture dynamics have a significant effect on overland flow generation. Catchment aspect is one of the major controlling factors of overland flow and soil moisture behaviour. A few experimental studies have been carried out in the uneven topography of the Himalayas. This study presents plot‐scale experiments using portable rainfall simulator at an altitude of 1,230 m above mean sea level and modelling of overland flow using observed datasets. Two plots were selected in 2 different aspects of Aglar watershed of Lesser Himalaya; the agro‐forested (AF) plot was positioned at the north aspect whereas the degraded (DE) plot was located at the south aspect of the hillslope. HS flumes and rain gauges were installed to measure the runoff at the outlet of the plot and the rainfall depth during rainfall simulation experiments. Moreover, 10 soil moisture sensors were installed at upslope and downslope locations of both the plots at 5, 15, 25, 35, and 45 cm depth from ground level to capture the soil moisture dynamics. The tests were conducted at intensities of 79.8 and 75 mm/hr in AF plot and 82.2 and 72 mm/hr in the DE plot during Test 1 and Test 2, respectively. The observed data indicate the presence of reinfiltration process only in the AF plot. The high water holding capacity and the presence of reinfiltration process results in less runoff volume in the AF plot compared with the DE plot. The Hortonian overland flow mechanism was found to be the dominant overland flow mechanism as only a few layers of top soil get saturated during all of the rainfall–runoff experiments. The runoff, rainfall, and soil moisture data were subsequently used to calibrate the parameters of HYDRUS‐2D overland flow module to simulate the runoff hydrograph and soil moisture. The components of hydrograph were evaluated in terms of peak discharge, runoff volume and time of concentration, the results were found to be within the satisfactory range. The goodness of fit of simulated hydrographs were more than 0.85 and 0.95 for AF and DE plot, respectively. The model produced satisfactory simulation results of soil moisture for all of the rainfall–runoff experiments. The HYDRUS‐2D overland flow module was found promising to simulate the runoff hydrograph and soil moisture in plot‐scale research.  相似文献   

Probabilities for the occurrences of medium to large earthquakes in northeast India and adjoining region     

R. B. S. Yadav  J. N. Tripathi  D. Shanker  B. K. Rastogi  M. C. Das  Vikas Kumar 《Natural Hazards》2011,56(1):145-167

The return periods and occurrence probabilities related to medium and large earthquakes (M _w 4.0–7.0) in four seismic zones in northeast India and adjoining region (20°–32°N and 87°–100°E) have been estimated with the help of well-known extreme value theory using three methods given by Gumbel (1958), Knopoff and Kagan (1977) and Bury (1999). In the present analysis, the return periods, the most probable maximum magnitude in a specified time period and probabilities of occurrences of earthquakes of magnitude M ≥ 4.0 have been computed using a homogeneous and complete earthquake catalogue prepared for the period between 1897 and 2007. The analysis indicates that the most probable largest annual earthquakes are close to 4.6, 5.1, 5.2, 5.5 and 5.8 in the four seismic zones, namely, the Shillong Plateau Zone, the Eastern Syntaxis Zone, the Himalayan Thrusts Zone, the Arakan-Yoma subduction zone and the whole region, respectively. The most probable largest earthquakes that may occur within different time periods have been also estimated and reported. The study reveals that the estimated mean return periods for the earthquake of magnitude M _w 6.5 are about 6–7 years, 9–10 years, 59–78 years, 72–115 years and 88–127 years in the whole region, the Arakan-Yoma subduction zone, the Himalayan Thrusts Zone, the Shillong Plateau Zone and the Eastern Syntaxis Zone, respectively. The study indicates that Arakan-Yoma subduction zone has the lowest mean return periods and high occurrence probability for the same earthquake magnitude in comparison to the other zones. The differences in the hazard parameters from zone to zone reveal the high crustal heterogeneity and seismotectonics complexity in northeast India and adjoining regions.  相似文献   

A review of strong motion studies in Gujarat State of western India     

Pallabee Choudhury  Sumer Chopra  Ketan Singha Roy  B. K. Rastogi 《Natural Hazards》2014,71(3):1241-1257

The present work reviews the strong motion studies done in Gujarat State of western India. Prior to the 2001 Bhuj earthquake, no strong motion instrument was in operation in Gujarat. After the earthquake, number of research institutes/universities from India and abroad deployed strong motion instruments to study aftershock activity, source dynamics, path and site effects. The strong motion recordings have enhanced the general understanding of the physics of earthquakes in the region. An attempt has been made to develop attenuation relationship for the Gujarat region from the actual ground motions recorded by the strong motion networks. The Government of Gujarat with the help from Asian Development Bank, World Bank (WB), Ministry of Science and Technology and Ministry of Earth Sciences, Government of India, has established a permanent dense network of strong motion accelerograph (SMA) all over Gujarat. In addition, the Institute of Seismological Research has been established in Gandhinagar, Gujarat, with the help of WB for carrying out seismological research. Recently, many important studies have been carried out using actual acceleration data obtained from a dense network of 54 SMA, as well as synthetic data generated using region-specific ground motion parameters. The recorded data are used to obtain region-specific ground motion parameters and ground motion prediction equation. A deterministic hazard analysis for the entire state of Gujarat has been carried out using site-specific ground motion parameters. The estimated peak ground acceleration and modified Mercalli intensity values have been used to estimate the vulnerability of the different types of buildings in 31 cities of Gujarat. As Gujarat has three distinct regions having varied geological conditions, the recorded strong motion data gave an opportunity to study the effect of geological and local-site conditions on the response spectra. This study for an intra-plate region like Gujarat is a pioneer work. Still, lots of research work need to be carried out as more and more data are available, such as development of more robust ground motion prediction equations and a 3D-velocity structure of Gujarat. Generation of shake maps in real time and a credible early earthquake warning system is need of the hour for disaster mitigation and management.  相似文献   

Source parameters and scaling relations for small earthquakes in the Kachchh region of Gujarat,India     

Santosh Kumar  Dinesh Kumar  B. K. Rastogi 《Natural Hazards》2014,73(3):1269-1289

The scaling relationships for stress drop and corner frequency with respect to magnitude have been worked out using 159 accelerograms from 34 small earthquakes (M _w 3.3–4.9) in the Kachchh region of Gujarat. The 318 spectra of P and S waves have been analyzed for this purpose. The average ratio of P- to S-wave corner frequency is found to be 1.19 suggestive of higher corner frequency for P wave as compared to that for S wave. The seismic moments estimated from P waves, M ₀(P), range from 1.98 × 10¹⁴ N m to 1.60 × 10¹⁶ N m and those from S waves, M ₀(S), range from 1.02 × 10¹⁴ N m to 3.4 × 10¹⁶ N m with an average ratio, M ₀(P)/M ₀(S), of 1.11. The total seismic energy varies from 1.83 × 10¹⁰ J to 2.84 × 10¹³ J. The estimated stress drop values do not depend on earthquake size significantly and lie in the range 30–120 bars for most of the events. A linear regression analysis between the estimated seismic moment (M ₀) and corner frequency (f _c) gives the scaling relation M ₀ f _c ³  = 7.6 × 10¹⁶ N m/s³. The proposed scaling laws are found to be consistent with similar scaling relations obtained in other seismically active regions of the world. Such an investigation should prove useful in seismic hazard and risk-related studies of the region. The relations developed in this study may be useful for the seismic hazard studies in the region.  相似文献