On the validity of time-predictable model for earthquake generation in north-east India

North-east India is seismically very active and has experienced many widelydistributed shallow, large earthquakes. Earthquake generation model for the region was studied using seismicity data [(1906–1984) prepared by National Geophysical Data Centre (NGDC), Boulder Colorado, USA]. For establishing statistical relations surface wave magnitudes (M _s≥5·5) have been considered. In the region four seismogenic sources have been identified which show the occurrences of atleast three earthquakes of magnitude 5·5≤M _s≤7·5 giving two repeat times. It is observed that the time interval between the two consecutive main shock depends on the preceding main shock magnitude (M _p) and not on the following main shock magnitude (M _f) revealing the validity of time predictable model for the region. Linear relation between logarithm of repeat time (T) and preceding main shock magnitude (M _p) is established in the form of logT=cM _p+a. The values ofc anda are estimated to be 0–36 and 1–23, respectively. The relation may be used for seismic hazard evaluation in the region.     

Geological and laboratory evidence for early generation of large amounts of liquid hydrocarbons from suberinite and subereous components

Suberinite, and subereous components of amorphous nature, comprise largely unrecognized, proficient sources of liquid hydrocarbons. Due to difficulties in recognizing the presence of subereous components and suberinite in organic sediments, the contributions of these liptinitic components to the organic input of source rocks are easily underestimated. Severe chemical alterations of suberinite in the vitrinite reflectance range of R_o = 0.35–0.60% are demonstrated. Organic geochemical data, obtained from samples subjected to natural maturation, reveal that subereous components/suberinite undergoes early thermal degradation to generate large amounts of hydrocarbons below R_o = 0.60%. Data obtained from laboratory maturation of immature, suberinite-rich coals indicate that about 50% of the potential of suberinite for generating C₁₂₊ hydrocarbons has already been exhausted during natural maturation of the samples, prior to the onset of the traditionally defined “oil window”. The present data (a) contradict the assumption that suberinite is mainly sourced by selective preservation/enrichment of a stable, highly aliphatic biopolymer, i.e. “suberan” and (b) suggest that suberinite contains appreciable amounts of aliphatic and aromatic moieties which are released at low thermal stress.     

Mineral equilibrium constraints on the feasibility of diffusive H2O-fluxed melting in the continental crust

Generation of granitic melt is believed to occur predominantly by melting through the breakdown of hydrous minerals. However, melting due to the influx of H₂O has been recognized in anatectic amphibolite facies tonalitic grey gneisses, metagreywackes and low-P metapelites, and has consequently been proposed as an alternative mechanism for the generation of granitic melt. Melting induced by H₂O addition is recognized from voluminous melt production at relatively low temperature, where hydrous minerals are stable and anhydrous minerals are preferentially consumed during melting. Mineral equilibrium modelling to determine the P–T conditions, melt volumes, melting reactions and viable H₂O sources reveals that the process is not restricted to specific compositions or P–T conditions, although lower pressure and lithologies with a low hydrous mineral content are more favourable. Melting reactions in all lithologies primarily consume quartz and feldspars to yield 5–6 mol.% melt for each mol.% of H₂O added. remains constant at ~0.70 to 0.77 during progressive melting as long as alkali feldspar is present. Once alkali feldspar is exhausted, plagioclase becomes the main reactant, producing more tonalitic melt compositions with gradually higher . Our results demonstrate that, at the site of melting, melting is driven by diffusion of H₂O into the target rock along chemical potential gradients, rather than the advective flow of a mechanically distinct water-rich fluid phase. Melting will initiate and proceed as long as a gradient exists between the H₂O source and target lithology. Our calculations show that an ordinary magma, such as an I-type magma with typical H₂O content, has a high enough to be a viable H₂O source, allowing diffusive H₂O-fluxed melting to produce melt proportions and fertility comparable to that of dehydration melting. However, high degrees of partial melting require a considerable amount of H₂O, which necessitates a continuously advecting H₂O source such as a magma conduit or melt-bearing shear zone. A magmatic H₂O source at emplacement level will undergo a similar amount of crystallization as the melt fraction produced in the target rock such that there will be no net melt production. Considering that shear-zone hosted magma conduits are localized features, diffusive H₂O-fluxed melting is likely to only be viable in a small fraction of the anatectic orogenic crust. Although it may play an important role in locally raising melt volumes and modifying magma chemistry through mingling and hybridization, it does not appear to, of itself, be able to generate significant volumes of granitic melt.     

构造活动和火山作用对干酪根成烃转化的影响

盆地构造活动和火山作用可以促进干酪根的成烃转化。构造活动的影响表现在力化学作用上；火山活动的影响除了表现为加热作用外，还表现为与火山岩有关的矿物与有机质或干酪根的相互作用，包括催化和加氢作用。黄铁矿被证明是一种更有效的催化剂。这些影响是附加在正常的干酪根热解作用上，而且构造活动和火山作用的影响也是复合在一起的。一些模拟实验证实了上述作用的存在以及对于不同的干酪根类型所施加影响的程度是不同的。     

两种侏罗系煤的油气生成定量对比研究

在加水热模拟条件下通过对不同有机质类型煤的生油气特征及其演化的对比研究,校正模拟实验的Ro,建立了油气生成的定量数学模型。研究认为,煤的油气生成特征与其有机质类型和演化阶段有关:高碳煤的有机碳含量变化不明显,甚至有增加的趋势,不必恢复其有机质丰度;低碳煤的有机碳含量随演化程度的增加而降低,但幅度不大,对其有机碳含量可适当恢复。煤的生油量大小与其有机质类型的好坏成正比,气油比则与有机质类型、成熟程度有密切的关系。在高过成熟阶段,有机质类型越好,气油比越高,气态烃生成量越大;而有机质类型越差,气油比越低,气态烃生成量越小。     

松辽盆地石炭-二叠系烃源岩研究

松辽盆地石炭-二叠系是烃源岩，沉积埋藏史可划分出持续深埋型、平衡埋藏型和短暂浅埋型3种类型。早白垩世晚期，石炭—二叠系烃源岩地温又一次达到并超过90℃，开始第二期生烃，油、气并生。这一时期，有效供烃区位于盆地东南部农安地区、西北部黑鱼泡地区，生气强度超过了生油强度。通过对石炭—二叠系沉积埋藏史、有机质热演化史和生烃史研究，无论对于深层找气，还是对盆地中新生代地层的油气勘探都具有十分重要的地质意义。     

The future of family farming in Israel: the second generation in the Moshav

The Moshav, a family farm-based settlement, has been a prime example of the major changes in the rural space in Israel. The aim of this paper is to present and understand these changes by studying the economic characteristics of second-generation – that is relatively younger – households in the Moshav. This group has shown a higher tendency to either adopt a livelihood strategy of pluriactivity, or to disassociate itself from agriculture in favour of non-agricultural income-generating activities, both inside and outside the settlement. Both trends have emerged in response to the increasing difficulty of deriving income from agriculture. The paper identifies the major patterns of economic activity and income sources among this group and assesses future attitudes towards operating the farm, choosing pluriactivity as a livelihood strategy, and remaining on the farm in the future.     

Spatial distribution of surface conditions and runoff generation in small arid watersheds, Zin Valley Badlands, Israel

High rill density may be regarded as indicative of frequent and integrated runoff along a drainage network. However, field observations of soil development and rill geometry in small, first-order catchments (0.1 to 1 ha) of the Zin Valley Badlands, northern Negev, Israel, suggest a pattern of partial area contribution and frequent flow discontinuities along hillslopes and channels. Changing soil properties, associated with an increase of slope angle and slope length, appear to be responsible for high infiltration on the slopes, leading to nonuniform runoff generation within small drainage basins. Runoff observation, sprinkling tests, and soil analysis along ridges and sideslopes were carried out to test this hypothesis. The results confirmed that infiltration capacity on the sideslopes is significantly higher than on the ridges. Under current rainfall conditions, only extreme rainfall intensities are sufficient to generate runoff along entire slopes. The discontinuous nature of most runoff events causes erosion on ridges and deposition on slopes, which enhances soil development on the valley sideslopes, creating a positive feedback on infiltration rate and depth. This demonstrates that the links between within-storm rainfall conditions and spatial distribution of soil characteristics have to be incorporated into our understanding of landscape development in badlands.     

Spot Revisited: Accuracy Assessment, Dem Generation and Validation from Stereo Spot 5 Hrg Images

SPOT 5 HRG Level 1A and 1B stereo scenes covering Zonguldak testfield in north-west Turkey have been analysed. They comprise the left and right image components with base to height ratio of 0·54. The pixel size on the ground is 5 m. The bundle orientation was executed by the PCI Geomatica V9.1.4 software package and resulted in 3D geopositioning to sub-pixel accuracies in each axis provided that at least six control points were used in the computation. Root mean square error (rmse) values and vectors of residual errors for Levels 1A and 1B are similar, even for different control and check point configurations. Based on the scene orientation, Level 1A and 1B digital elevation models (DEMs) of the testfield have been determined by automatic matching and validated by the reference DEM digitised from the 1:25 000 scale topographic maps, interferometric DEMs from Shuttle Radar Topography Mission (SRTM) X- and C-band SAR data and the GPS profiles measured along the main roads in the testfield. Although the accuracies of reference data-sets are too similar to the generated SPOT DEMs, these are the only high quality reference materials available in this area. Sub-pixel height accuracy was indicated by the comparison with profile points. However, they are in favourable locations where matching is always successful, so such a result may give a biased measure of the accuracy of the corresponding DEMs.