Coupling Between Seismic Activity and Hydrogeochemistry at the Shillong Plateau, Northeastern India     

Alasdair Skelton  Lillemor Claesson  Govinda Chakrapani  Chandan Mahanta  Joyanto Routh  Magnus Mörth  Param Khanna 《Pure and Applied Geophysics》2008,165(1):45-61

Transient hydrogeochemical anomalies were detected in a granite-hosted aquifer, which is located at a depth of 110 m, north of the Shillong Plateau, Assam, India, where groundwater chemistry is mainly buffered by feldspar alteration to kaolinite. Their onsets preceded moderate earthquakes on December 9, 2004 (M_W = 5.3) and February 15, 2005 (M_W = 5.0), respectively, 206 and 213 km from the aquifer. The ratios [Na+K]/Si, Na/K and [Na+K]/Ca, conductivity, alkalinity and chloride concentration began increasing 3–5 weeks before the M_W = 5.3 earthquake. By comparison with field, experimental and theoretical studies, we interpret a transient switchover between source aquifers, which induced an influx of groundwater from a second aquifer, where groundwater chemistry was dominantly buffered by the alteration of feldspar to smectite. This could have occurred in response to fracturing of a hydrological barrier. The ratio Ba/Sr began decreasing 3–6 days before the M_W = 5.0 earthquake. We interpret a transient switchover to anorthite dissolution caused by exposure of fresh plagioclase to groundwater interaction. This could have been induced by microfracturing, locally within the main aquifer. By comparison with experimental studies of feldspar dissolution, we interpret that hydrogeochemical recovery was facilitated by groundwater interaction and clay mineralization, which could have been coupled with fracture sealing. The coincidence in timing of these two hydrogeochemical events with the only two M_W ≥ 5 earthquakes in the study area argues in favor of cause-and-effect seismic-hydrogeochemical coupling. However, reasons for ambiguity include the lack of similar hydrogeochemical anomalies coupled with smaller seismic events near the monitoring station, the >200 km length scale of inferred seismic-hydrogeochemical coupling, and the potential for far-field effects related to the Great Sumatra–Andaman Islands Earthquake of December 26, 2004.  相似文献   

Estimation of Maximum Earthquakes in Northeast India   总被引：1，自引：0，他引：1  

K. K. S. Thingbaijam  S. K. Nath 《Pure and Applied Geophysics》2008,165(5):889-901

We attempt to estimate possible maximum earthquakes in the northeast Indian region for four seismic source zones, namely EHZ, MBZ, EBZ, and SHZ, which encapsulates the various seismogenic structures of the region and also for combined source zones taken as a single seismic source regime. The latter case exhibits a high maximum earthquake estimate of M_W 9.4 (±0.85) through Bayesian interpretation of frequency magnitude distribution with Gamma function implicating a moderate deviation from the standard Gutenberg Richter model at the higher magnitudes. However, tapering Gutenberg Richter models with corner magnitudes at M_W 8.01, 8.7 and 9.1, respectively indicated maximum values corresponding to M_W 8.4, 9.0, and 9.3. The former approach was applied to each of the source zones wherein the data are presented in parts according to the data completeness, thereof. EHZ, MBZ, EBZ and SHZ are seen with maximum earthquakes of M_W 8.35 (±0.59), 8.79 (±0.31), 8.20 (±0.50), and 8.73 (±0.70), respectively. The maximum possible earthquakes estimated for each individual zone are seen to be lower than that estimated for the single regime. However, the pertaining return periods estimated for the combined zone are far less than those estimated for the demarcated ones.  相似文献   

Ground motion parameters of Shillong plateau: One of the most seismically active zones of northeastern India     

Saurabh Baruah  Santanu Baruah  Naba Kumar Gogoi  Olga Erteleva  Felix Aptikaev  J. R. Kayal 《地震学报(英文版)》2009,(3):283-291

Strong ground motion parameters for Shillong plateau of northeastern India are examined. Empirical relations are obtained for main parameters of ground motions as a function of earthquake magnitude, fault type, source depth, velocity characterization of medium and distance. Correlation between ground motion parameters and characteristics of seismogenic zones are established. A new attenuation relation for peak ground acceleration is developed, which predicts higher expected PGA in the region. Parameters of ...  相似文献   

Microstructurally controlled monazite chronology of ultrahigh-temperature granulites from southern India: Implications for the timing of Gondwana assembly     

M. Santosh  Toshiaki  Tsunogae  Yukiyasu  Tsutsumi  Masayuki  Iwamura 《Island Arc》2009,18(2):248-265

Ultrahigh‐temperature (UHT) granulite facies rocks from the Achankovil Shear Zone area and the southern domain of the Madurai Granulite Block in South India contain monazite useful for in situ microprobe U–Pb dating. The UHT rocks examined consist of garnet + cordierite (retrograde) + quartz + mesoperthite + biotite + plagioclase + Fe‐Ti oxides ± orthopyroxene ± sillimanite and accessory zircon and monazite. Sillimanite occurs only as inclusions in garnet. Microstructural observations suggest garnet, orthopyroxene, spinel and mesoperthite are products of peak metamorphism. Post‐peak formation of cordierite ± orthopyroxene ± quartz and cordierite + spinel + Fe‐Ti oxides assemblages is also observed. Geothermobarometry on orthopyroxene and garnet‐orthopyroxene bearing assemblages suggest peak UHT conditions of T = 940–1040°C and P = 8.5–9.5 kbar. This was followed by a retrograde stage of 3.5–4.5 kbar and 720 ± 60°C, estimated from garnet‐cordierite assemblages. A small population of rounded, probably detrital, monazites in these rocks yield ages from Meso‐ to Neoproterozoic indicating a heterogeneous source. The youngest associated spot ages are 660–600 Ma suggesting protolith deposition up to ca 600 Ma. In contrast, the vast majority of monazites that crystallized during the latest metamorphic event show late Neoproterozoic to Cambrian ages. Probability‐density plots of monazite age data show a ‘peak’ between 533 and 565 Ma, but this peak need not reflect a particular thermal event. Collating ages from homogenous metamorphic monazites associated with minerals stable at peak P‐T conditions suggests peak metamorphism in these rocks occurred at 580–600 Ma. Together with a re‐evaluation of available data from adjacent granulite blocks in southern India, these data suggest the main metamorphic event coinciding with the suturing of India with the Gondwana amalgam probably occurred 580–600 Ma. The 500–550 Ma ages commonly reported in previous studies might represent post‐peak thermal events.  相似文献   

Attenuation of coda waves in the Northeastern Region of India   总被引：1，自引：0，他引：1  

Devajit Hazarika  Saurabh Baruah  Naba Kumar Gogoi 《Journal of Seismology》2009,13(1):141-160

Coda wave attenuation quality factor Qc is estimated in the northeastern region of India using 45 local earthquakes recorded by regional seismic network. The quality factor Qc was estimated using the single backscattering model modified by Sato (J Phys Earth 25:27–41, 1977), in the frequency range 1–18 Hz. The attenuation and frequency dependence for different paths and the correlation of the results with geotectonics of the region are described in this paper. A total of 3,890 Qc measurements covering 187 varying paths are made for different lapse time window of 20, 30, 40, 50, 60, 70, 80, and 90 s in coda wave. The magnitudes of the analyzed events range from 1.2 to 3.9 and focal depths range between 7 and 38 km. The source–receiver distances of the selected events range between 16 and 270 km. For 30-s duration, the mean values of the estimated Qc vary from 50 ± 12 (at 1 Hz) to 2,078 ± 211(at 18 Hz) for the Arunachal Himalaya, 49 ± 14 (at 1 Hz) to 2,466 ± 197 (at 18 Hz) for the Indo-Burman, and 45 ± 13 (at 1 Hz) to 2,069 ± 198 (at 18 Hz) for Shillong group of earthquakes. It is observed that Qc increases with frequency portraying an average attenuation relation for the region. Moreover, the pattern of Qc^− 1 with frequency is analogous to the estimates obtained in other tectonic areas in the world, except with the observation that the Qc^− 1 is much higher at 1 Hz for the northeastern region. The Qc^− 1 is about 10^− 1.8 at 1 Hz and decreases to about 10^− 3.6 at 18 Hz indicating clear frequency dependence. Pertaining to the spatial distribution of Qc values, Mikir Hills and western part of Shillong Plateau are characterized by lower attenuation.  相似文献   

Groundwater governmentality: hegemony and technologies of resistance in Rajasthan's (India) groundwater governance     

TREVOR BIRKENHOLTZ 《The Geographical journal》2009,175(3):208-220

Globally, decentralisation has become the dominant paradigm for environmental governance. This paper explores the linkages between green governmentality approaches to subjectivity and Gramscian notions of hegemony to examine recent efforts in Rajasthan, India to decentralise groundwater governance through targeted formal regulations and outreach activities, such as water awareness campaigns ( Jal Abhiyaan ). The latter seeks to alter the beliefs and practices of farmers by institutionalising their support for state groundwater conservation efforts, including privatisation. The paper draws on household surveys and interviews with farmers and government agents to examine the relationship between the political economic motivations for and practices of state subject-making and differential resistance to these efforts based on farmers' multiple subject positions. Findings suggest, first, that the state is motivated through its monetary and advisory relationship with donor agencies, such as the World Bank. Through both outreach activities and coercion, it attempts to gain 'consent' for its proposals, which devolve state control rather than truly decentralising decision-making, to make self-conducting and willing subjects of specifically neoliberal groundwater conservation. But, second, these attempts are being resisted by some farmers through protests, informal discussions, non-participation, and the collectivisation of access to groundwater and irrigation through irrigation partnerships. Third, resistance to these efforts, or support for them, is different between farmers based on their multiple subjectivities (caste, class and ecological conditions). The paper advances both our understanding of the processes of environmental subject-making and of the devolution of environmental governance, by integrating the lessons from governmentality and Gramscian approaches to social power and subjectivity.  相似文献   

The value of commodity biographies: integrating tribal farmers in India into a global organic agro-food network     

Martin Franz  Markus Hassler 《Area》2010,42(1):25-34

The production of organic food has been regarded for a long time as being synonymous with ecological regional production systems. However, the increased production of organic food products has led to an ongoing industrialisation and also to a global spread of network structures within this segment of agriculture. This paper provides a case study of the integration of organic pepper farmers from an indigenous tribe in Kerala, India, into global agro-food networks, linking them to a German producer of organic meat products. The results of this study show that the importance of the territorial embeddedness and the abandonment of the exercise of power can be crucial for the success of global organic agro-food networks.  相似文献   

Origin and Geological Significance of TTG Gneisses from the Maevatanana Greenstone Belt in North–Central Madagascar, and A Comparison with India     

LI Peng  LI Jiankang  LIU Shanbao  PEI Rongfu  SHI Guanghai 《《地质学报》英文版》2017,91(3):1003-1024

The Maevatanana greenstone belt in north-central Madagascar contains widespread exposures of tonalite-trondhjemite-granodiorite(TTG) gneisses,and is important for its concentrations of various metal deposits(e.g.,chromium,nickle,iron,gold).In this paper we report on the petrography,and major and trace element compositions of the TTG gneisses within the Berere Complex of the Maevatanana area,as well as LA-ICP-MS U-Pb ages and Lu-Hf isotopic compositions of zircons from the gneisses.The gneisses consist mainly of granitoid gneiss and biotite(±hornblende) plagiogneiss,and analysis of thin sections provides evidence of crushing,recrystallization,and metasomatism related to dynamic metamorphism.Samples have large variations in their major and trace element contents,with SiO_2 = 55.87-68.06 wt%,Al_2O_3 = 13.9-17.8 wt%,and Na_2O/K_2O =0.97-2.13.Geochemically,the granitoid gneisses and biotite plagiogneisses fall on a low-Al trondhjemite to granodiorite trend,while the biotite-hornblende plagiogneisses represent a high-Al tonalite TTG assemblage.Zircon U-Pb dating shows that the Berere Complex TTG gneisses formed at2.5-2.4 Ga.Most ε_(Hf(t)) values of zircons from the biotite(± hornblende) plagiogneisses are positive,while most ε_(Hf(t)) values from the granitoid gneisses are negative,suggesting a degree of crustal contamination.Two-stage Hf model ages suggest that the age of the protolith of the TTG gneisses was ca.3.4-2.6 Ga,representing a period of paleocontinent formation in the Mesoarchean.Geothermometries indicate the temperature of metamorphism of the TTG gneisses was 522-612℃.Based on these data,the protolith of the TTG gneisses is inferred to have formed during the development of a Mesoarchean paleocontinent that is now widely exposed as a TTG gneiss belt(mostly lower amphibolite facies) in the Maevatanana area,and which records a geological evolution related to the subduction of an ancient oceanic crust and the collision of microcontinents during the formation of the Rodinia supercontinent.The lithological similarity of Precambrian basement,the close ages of metamorphism within greenstone belts and the comparable distribution of metamorphic grade all show a pronounced Precambrian geology similarity between Madagascar and India,which can provide significative clues in understanding the possible Precambrian Supercontinent tectonics,and also important constraints on the correlation of the two continental fragments.  相似文献   

未来20年印度资源需求预测及中国应对策略研究     

李晓明  王安建 《地球学报》2017,38(1):45-53

印度已经成为全球重要的国家之一。文章系统分析了印度的人口、经济发展特点,印度在过去发展过程中能源、铁、铜、铝资源的消费历史。并选用了合理的经济分析模型、资源需求预测方法,参考权威机构的研究成果,如资源需求"S"形规律、"GDP增速‘钟’形规律"以及格罗宁根研究中心(简称GGDC)、世界银行等机构的数据,科学、合理地预测了印度人口、经济及资源需求。认为:1)在工业化的带动下,印度经济具有再创神话的潜力;2)印度对能源、铁、铜、铝的需求将随着工业化进程的推进而快速上升,印度将成为继中国后拉动全球资源需求的"新引擎";3)印度发展不仅带给我国产业升级带来了新机遇,同时也是我国强有力的竞争者,比如在资源获取方面的竞争。因此我国企业应加强自身的核心竞争力,在印度发展的过程中获得好的机会成长。  相似文献   

Climatic periodicities recorded in lake sediment magnetic susceptibility data: Further evidence for solar forcing on Indian summer monsoon   总被引：1，自引：0，他引：1  

Anish Kumar Warrier  Kizhur Sandeep  Rajasekharaiah Shankar 《地学前缘(英文版)》2017,8(6):1349-1355

The Indian summer monsoon exhibits considerable spatio-temporal variability.It is therefore important to understand its dynamics and the inherent periodicities.In this study,we have performed spectral and wavelet analyses of magnetic susceptibility data for sediments from Thimmannanayakanakere(TK)-a small lake in southern India.The main objective of this investigation is to identify and explain the possible origin of the prominent periodicities present in the magnetic susceptibility data.Significant periodicities in the TK χ_(lf)data are centered at 906,232,147,128,96,61,54 and 44 years,which might have a solar origin.The wavelet power spectrum of the raw and detrended χ_(lf)data confirms the findings of spectral analysis and also provides temporal variations of the significant cyclicities during the past3700 cal.years B.P.Positive correlation is documented between sunspot activity and TK xif data;crossspectral analysis of the reconstructed sunspot data and TK xif data suggest that there is a strong coherence between the two datasets as significant periodicities are documented in both.There is a good match between the TK xif and the reconstructed total solar irradiance data for the past 1200 years.However,an out-of-phase relationship is documented at certain time-intervals,which may be attributed to uncertainties in the age-depth model.The results obtained from this study show that solar variations are the main controlling factor of the southwest monsoon and,like other archives from different regions in India,the TK lake sediments have also recorded these solar signatures.  相似文献