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991.
D. Shanker H. N. Singh H. Paudyal A. Kumar A. Panthi V. P. Singh 《Pure and Applied Geophysics》2010,167(6-7):655-666
A long-range correlation between earthquakes is indicated by some phenomena precursory to strong earthquakes. Most of the major earthquakes show prior seismic activity that in hindsight seems anomalous. The features include changes in regional activity rate and changes in the pattern of small earthquakes, including alignments on unmapped linear features near the (future) main shock. It has long been suggested that large earthquakes are preceded by observable variations in regional seismicity. Studies on seismic precursors preceding large to great earthquakes with M ≥ 7.5 were carried out in the northeast India region bounded by the area 20°–32°N and 88°–100°E using the earthquake database from 1853 to 1988. It is observed that all earthquakes of M ≥ 7.5, including the two great earthquakes of 1897 and 1950, were preceded by abnormally low anomalous seismicity phases some 11–27 years prior to their occurrence. On the other hand, precursory time periods ranged from 440 to 1,768 days for main shocks with M 5.6–6.5 for the period from 1963 to 1988. Furthermore, the 6 August, 1988 main shock of M 7.5 in the Arakan Yoma fold belt was preceded by well-defined patterns of anomalous seismicity that occurred during 1963–1964, about 25.2 years prior to its occurrence. The pattern of anomalous seismicity in the form of earthquake swarms preceding major earthquakes in the northeast India region can be regarded as one of the potential seismic precursors. Database constraints have been the main barrier to searching for this precursor preceding smaller earthquakes, which otherwise might have provided additional information on its existence. The entire exercise indicates that anomalous seismicity preceding major shocks is a common seismic pattern for the northeast India region, and can be employed for long-range earthquake prediction when better quality seismological data sets covering a wide range of magnitudes are available. Anomalous seismic activity is distinguished by a much higher annual frequency of earthquake occurrence than in the preceding normal and the following gap episodes. 相似文献
992.
Ram Bichar Singh Yadav Jayant Nath Tripathi Bal Krishna Rastogi Mridul Chandra Das Sumer Chopra 《Pure and Applied Geophysics》2010,167(11):1331-1342
Northeast India and adjoining regions (20°–32° N and 87°–100° E) are highly vulnerable to earthquake hazard in the Indian
sub-continent, which fall under seismic zones V, IV and III in the seismic zoning map of India with magnitudes M exceeding 8, 7 and 6, respectively. It has experienced two devastating earthquakes, namely, the Shillong Plateau earthquake
of June 12, 1897 (M
w
8.1) and the Assam earthquake of August 15, 1950 (M
w
8.5) that caused huge loss of lives and property in the Indian sub-continent. In the present study, the probabilities of
the occurrences of earthquakes with magnitude M ≥ 7.0 during a specified interval of time has been estimated on the basis of three probabilistic models, namely, Weibull,
Gamma and Lognormal, with the help of the earthquake catalogue spanning the period 1846 to 1995. The method of maximum likelihood
has been used to estimate the earthquake hazard parameters. The logarithmic probability of likelihood function (ln L) is estimated
and used to compare the suitability of models and it was found that the Gamma model fits best with the actual data. The sample
mean interval of occurrence of such earthquakes is estimated as 7.82 years in the northeast India region and the expected
mean values for Weibull, Gamma and Lognormal distributions are estimated as 7.837, 7.820 and 8.269 years, respectively. The
estimated cumulative probability for an earthquake M ≥ 7.0 reaches 0.8 after about 15–16 (2010–2011) years and 0.9 after about 18–20 (2013–2015) years from the occurrence of
the last earthquake (1995) in the region. The estimated conditional probability also reaches 0.8 to 0.9 after about 13–17
(2008–2012) years in the considered region for an earthquake M ≥ 7.0 when the elapsed time is zero years. However, the conditional probability reaches 0.8 to 0.9 after about 9–13 (2018–2022)
years for earthquake M ≥ 7.0 when the elapsed time is 14 years (i.e. 2009). 相似文献
993.
The study presents a fast imaging technique for the very low‐frequency data interpretation. First, an analytical expression was derived to compute the vertical component of the magnetic field at any point on the Earth's surface for a given current density distribution in a rectangular block on the subsurface. Current density is considered as exponentially decreasing with depth, according to the skin depth rule in a particular block. Subsequently, the vertical component of the magnetic field due to the entire subsurface was computed as the sum of the vertical component of the magnetic field due to an individual block. Since the vertical component of the magnetic field is proportional to the real part of very low‐frequency anomaly, an inversion program was developed for imaging of the subsurface conductors using the real very low‐frequency anomaly in terms of apparent current density distribution in the subsurface. Imaging results from the presented formulation were compared with other imaging techniques in terms of apparent current density and resistivity distribution using a standard numerical forward modelling and inversion technique. Efficacy of the developed approach was demonstrated for the interpretation of synthetic and field very low‐frequency data. The presented imaging technique shows improvement with respect to the filtering approaches in depicting subsurface conductors. Further, results obtained using the presented approach are closer to the results of rigorous resistivity inversion. Since the presented approach uses only the real anomaly, which is not sensitive to very small isolated near‐surface conducting features, it depicts prominent conducting features in the subsurface. 相似文献
994.
Xiaoling Su Vijay P. Singh Jiping Niu Lina Hao 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(6):1571-1582
Drought/wetness conditions are fundamental not only for agricultural production but also ecology, human health, and economic activity. Dryness/wetness is a function of precipitation, temperature, vegetation and potential evapotranspiration. Regions with low moisture are often characterized by aridity which, in turn, reflects the degree of meteorological drought. Observed climatic data from eleven meteorological stations in and around Shiyang River basin, China, were used to calculate the aridity index (AI) which was defined as the ratio of potential evapotranspiration (ET0) to precipitation (P). ET0 was calculated using the Penman–Monteith method. The ordinary kriging method was used to interpolate the spatial variability of ET0, P and AI. The Mann–Kendall test with a pre-whitening method was employed using the Yue and Wang autocorrelation correction to detect temporal trends. The Theil–Sen estimator was used to estimate the slopes of trend lines. Results showed a higher AI in the north basin and a lower AI in the Qilian Mountain region. Annual ET0 and P had increasing trends with a slope of 0.672 and 0.459 mm per year, respectively, but trends were not statistically significant for most stations. While annual AI had a slight decreasing trend with a slope of ?0.01 per year, the trend was not statistically significant for all stations. The decreasing trends in winter AI (at a rate of ?0.313/a) was more significant than that in other seasons. The study indicates that the Shiyang River basin is getting slightly wetter, especially in winter. 相似文献
995.
996.
Seismic site coefficients (F s ) for Imphal city have been estimated based on 700 synthetically generated earthquake time histories through stochastic finite fault method, considering various combinations of magnitudes and fault distances that may affect Imphal city. Seismic hazard curves and Uniform Hazard Response Spectra (UHRS) are presented for Imphal city. F s have been estimated based on site response analyses through SHAKE-91 for a period range of engineering interest (PGA to 3.0 s), for 5% damping. F s were multiplied by UHRS values to obtain surface level spectral acceleration with 2 and 10% probability of exceedance in 50 year (~2500 and ~500 year) return period. Comparison between predicted mean surface level response spectra and IS-1893 code shows that spectral acceleration value is higher for longer periods (i.e., >1.0 s), for ~500 year return period, and lower for periods shorter than 0.2 s for ~2500 year return period. 相似文献
997.
Vimal Chandra Pandey Jay Shankar Singh Akhilesh Kumar D. D. Tewari 《洁净——土壤、空气、水》2010,38(12):1116-1123
Chickpea grown in fly ash (FA) treated soil (25, 50, and 100% FA) was used to evaluate the effect of FA on antioxidants, metal concentration (Fe, Zn, Cu, Cr, and Cd), photosynthetic pigments (chlorophyll a (chl‐a), chlorophyll b (chl‐b), total chlorophyll (total chl), and carotenoids), growth and yield performance. All antioxidants in roots, shoots and leaves of chickpea increase with increasing FA doses to combat FA stress. The activities of antioxidants were more in the root tissues to cope with stress induced in the plants as compared to shoot and leaf. Concentration of metals was found maximum in roots than the shoots and seeds. The highest concentration of Fe and lowest level of Cd were recorded in all treatments of FA for different parts of the plant. The treated crop showed reduced level of chlorophyll but enhanced level of carotenoids and protein. However, root length, number of nodules and biomass in 25 and 50% FA treatments did not differ significantly in comparison to respective control plants. These results suggest that heavy metals of FA causes oxidative stress in this crop and the antioxidant enzymes could help a pivotal role against oxidative injury. 相似文献
998.
Pseudomonas putida MHF 7109 has been isolated and identified from cow dung microbial consortium for biodegradation of selected petroleum hydrocarbon compounds – benzene, toluene, and o‐xylene (BTX). Each compound was applied separately at concentrations of 50, 100, 250, and 500 mg L?1 in minimal salt medium to evaluate degradation activity of the identified microbial strain. The results indicated that the strain used has high potential to degrade BTX at a concentration of 50 mg L?1 within a period of 48, 96, and 168 h, respectively; whereas the concentration of 100 mg L?1 of benzene and toluene was found to be completely degraded within 120 and 168 h, respectively. Sixty‐two percent of o‐xylene were degraded within 168 h at the 100 mg L?1 concentration level. The maximum degradation rates for BTX were 1.35, 1.04, and 0.51 mg L?1 h?1, respectively. At higher concentrations (250 and 500 mg L?1) BTX inhibited the activity of microorganisms. The mass spectrometry analysis identified the intermediates as catechol, 2‐hydroxymuconic semialdehyde, 3‐methylcatechol, cis‐2‐hydroxypenta‐2,4‐dienoate, 2‐methylbenzyl alcohol, and 1,2‐dihydroxy‐6‐methylcyclohexa‐3,5‐dienecarboxylate, for BTX, respectively. P. putida MHF 7109 has been found to have high potential for biodegradation of volatile petroleum hydrocarbons. 相似文献
999.
An atlas of isoseismal maps for South Africa, dating from as far back as 1932–2005, is provided. This work involved searching
through historical reports to find records of macroseismic effects. In many instances, when there was a large tremor, questionnaires
were distributed to local towns to assess the severity of the tremor and the damage it caused. Based on the results of these
questionnaires and site investigations, isoseismal maps were drawn. These isoseismal maps were revisited and digitised for
this study. Five additional isoseismal maps were prepared by the authors based on the results of questionnaires alone. Most
isoseismal maps in the historical record use the Modified Mercalli scale. All maps are hence provided according to this scale.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
1000.
Aquifer characteristics and its modeling around an industrial complex,Tuticorin, Tamil Nadu,India: A case study 总被引:3,自引:0,他引:3
Anthropogenic pollution of shallow groundwater resources due to industrial activities is becoming a cause of concern in the
east coastal belt of the state of Tamil Nadu, India. Integrated hydrogeological, geophysical and tracer studies were carried
out in the coastal region encompassing an industrial complex. The objective has been to gain knowledge of aquifer characteristics,
ascertaining groundwater movement and its flow direction, which would in turn reveal the possibility of contamination of groundwater
regime and its better management. The results of multi-parameters and model study indicate that the velocity of groundwater
flow ranges from 0.013 m/d to 0.22m/d in and around the industrial complex in upstream western part of the catchment and 0.026
m/d to 0.054m/d in the downstream eastern part, near the coast. These parameters are vital for the development of groundwater
management scheme. 相似文献