北京及邻区微震活动的初步分析

通过对北京遥测地震台网近年来记录到的北京及邻区地震的震中分布,地震活动频度及能量释放强度的分析,得到本区地震活动在时间分布上具有“聚堆性”。在年发震频度,地震强度和能释放方面均具有双峰值特征,并且具有较好的一致性和同步性,在空间分布上具有条带特征,且形成北东～南西和北西～南东的两条相互交汇的条带。又通过统计分析得到本区发震概率最大的时间段是每年的１０月前后,而地震主要发生在北西～南东带上。     

抓“热点”、解“难点”，依法行政搞矿管

原达县地区是全省矿业活动最频繁的地区之一,也一度成了全省有名的“采煤混战”大区。近几年来,以《矿产资源法》为指针,抓住“重点”,调处“热点”,解决“难点”,以点带面,加强矿管行政执法工作,促进了全区矿业秩序的全面好转,矿业生产也相应得到健康发展。矿业产值占全区工业总产值的１５％左右,是全区的一大支柱产业,有力地促进了地方经济的发展。     

半干旱区高效生态农业发展问题及对策研究——以陇东黄土高原环县为例

生态农业是当今农业发展的方向。也是区域农业高效发展的必由之路，环县农业存在结构不合理，产业化进程缓慢，生产基础薄弱，生态环境恶化等问题。欲使生态农业高效发展，应把资源、环境与农业经济发展结合起来，采取调整产业结构、建立高效生态农业发展模式、加快龙头企业的发展、加大资金和科技投入、保护和改善生态环境等措施。     

Increasing critical sensitivity of the Load/Unload Response Ratio before large earthquakes with identified stress accumulation pattern

The Load/Unload Response Ratio (LURR) method is proposed for short-to-intermediate-term earthquake prediction [Yin, X.C., Chen, X.Z., Song, Z.P., Yin, C., 1995. A New Approach to Earthquake Prediction — The Load/Unload Response Ratio (LURR) Theory, Pure Appl. Geophys., 145, 701–715]. This method is based on measuring the ratio between Benioff strains released during the time periods of loading and unloading, corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults. According to the method, the LURR time series usually climb to an anomalously high peak prior to occurrence of a large earthquake. Previous studies have indicated that the size of critical seismogenic region selected for LURR measurements has great influence on the evaluation of LURR. In this study, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. The Coulomb stress change before a hypothetical earthquake is calculated based on a simple back-slip dislocation model of the event. This new algorithm, by combining the LURR method with our choice of identified area with increased Coulomb stress, is devised to improve the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. Retrospective tests of this algorithm on four large earthquakes occurred in California over the last two decades show remarkable enhancement of the LURR precursory anomalies. For some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods, significant anomalies are found if circular areas are used, and are not found if increased Coulomb stress areas are used for LURR data selection. The unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events.     

A novel strategy using biodegradable EDDS for the chemically enhanced phytoextraction of soils contaminated with heavy metals

For the sake of cost and potential environmental risk, it is necessary to minimize the amount of chelates used in chemically-enhanced phytoextraction. In the present study, a biodegradable chelating agent, EDDS was added in a hot solution at 90℃ to the soil in which garland chrysanthemum （Chrysanthemum coronarium L.） and beans （Phaseolus vulgaris L., white bean） were growing. The application of hot chelate solutions was much more efficient than the application of normal chelate solutions （25℃） in improving the uptake of heavy metals by plants. When 1 mmol kg1 of EDDS as a hot solution was applied to soil, the concentrations ofCu, Zn and Cd and the total phytoextraction by the shoots of the two plant species exceeded or approximated those in the shoots of plants treated with 5 mmol kg^-1 of normal EDTA solution. The concentrations of metals in the shoots of beans were significantly correlated with the relative electrolyte leakage rate of root cells, indicating that the root damage resulting from the hot solution might play an important role in the process of chelate-enhanced metal uptake. The soil leaching study demonstrated that decreasing the dosage of chelate resulted in decreased concentrations of soluble metals in soils. On the 28th day following the application of chelate, the concentrations of soluble metals in the EDDS treated soil were not significantly different from the concentrations in the control soil to which chelates had not been applied.     

An Albian–Cenomanian unconformity in the northern Andes: Evidence and tectonic significance

The Villeta Group of Colombia and equivalent stratigraphic units of Venezuela and Ecuador comprise marine sequences ranging from Albian to Santonian in age. Deposition of the Villeta Group was presumed to take place entirely in quiet tectonic conditions in a passive margin setting that occupied NW South America. From a large database of 2D/3D seismic, well, surface geology, and biostratigraphic data, we present evidence for intra-Villeta (mostly late Albian–Cenomanian) deformation in parts of the Upper Magdalena Valley and Eastern Cordillera of Colombia, controlled by transpressional fault reactivation, produced by transpressional fault reactivation and thrusting that resulted in an angular unconformity. This event has been largely unnoticed in the literature, but previously scattered evidence supports our observations, suggesting regionally extensive tectonism. Published fission-track age determinations and other geologic evidence from Colombia and Venezuela suggest significant uplifts around 80–100 m.y., which may reflect changes in the subduction regime, with compressional deformation in certain regions and extensional deformation in others. A late Albian onset of compressional deformation along the Colombian and Peruvian segments of the Andes may be related to the opening of the South Atlantic Ocean at equatorial latitudes. Identification of tectonic activity with development of an unconformity in intra-Villeta times provides new insights into understanding the evolution of the Upper Magdalena Valley and adjacent areas of Colombia and western Venezuela and creates new possibilities for hydrocarbon exploration, with additional trapping phases, better reservoir preservation by early migration and secondary porosity, and ultimately facies changes with stratigraphic potential.     

3-D seismic structure of the source area of the 1993 Latur, India, earthquake and its implications for rupture nucleations

The Latur earthquake (M_w 6.1) of 29 September 1993 is a rare stable continental region (SCR) earthquake that occurred on a previously unknown blind fault. In this study, we determined detailed three-dimensional (3-D) P- and S-wave velocity (V_p, V_s) and Poisson's ratio (σ) structures by inverting the first P- and S-wave high-quality arrival time data from 142 aftershocks that were recorded by a network of temporary seismic stations. The source zone of the Latur earthquake shows strong lateral heterogeneities in V_p, V_s and σ structures, extending in a volume of about 90 × 90 × 15 km³. The mainshock occurred within, but near the boundary, of a low-V_p, high-V_s and low-σ zone. This suggests that the structural asperities at the mainshock hypocenter are associated with a partially fluid-saturated fractured rock in a previously unknown source zone with intersecting fault surfaces. This might have triggered the 1993 Latur mainshock and its aftershock sequence. Our results are in good agreement with other geophysical studies that suggest high conductivity and high concentration of radiogenic helium gas beneath the source zone of the Latur earthquake. Our study provides an additional evidence for the presence of fluid related anomaly at the hidden source zone of the Latur earthquake in the SCR and helps us understand the genesis of damaging earthquakes in the SCR of the world.     

Geophysical methods applied to fault characterization and earthquake potential assessment in the Lower Tagus Valley, Portugal

The study region is located in the Lower Tagus Valley, central Portugal, and includes a large portion of the densely populated area of Lisbon. It is characterized by a moderate seismicity with a diffuse pattern, with historical earthquakes causing many casualties, serious damage and economic losses. Occurrence of earthquakes in the area indicates the presence of seismogenic structures at depth that are deficiently known due to a thick Cenozoic sedimentary cover. The hidden character of many of the faults in the Lower Tagus Valley requires the use of indirect methodologies for their study. This paper focuses on the application of high-resolution seismic reflection method for the detection of near-surface faulting on two major tectonic structures that are hidden under the recent alluvial cover of the Tagus Valley, and that have been recognized on deep oil-industry seismic reflection profiles and/or inferred from the surface geology. These are a WNW–ESE-trending fault zone located within the Lower Tagus Cenozoic basin, across the Tagus River estuary (Porto Alto fault), and a NNE–SSW-trending reverse fault zone that borders the Cenozoic Basin at the W (Vila Franca de Xira–Lisbon fault). Vertical electrical soundings were also acquired over the seismic profiles and the refraction interpretation of the reflection data was carried out. According to the interpretation of the collected data, a complex fault pattern disrupts the near surface (first 400 m) at Porto Alto, affecting the Upper Neogene and (at least for one fault) the Quaternary, with a normal offset component. The consistency with the previous oil-industry profiles interpretation supports the location and geometry of this fault zone. Concerning the second structure, two major faults were detected north of Vila Franca de Xira, supporting the extension of the Vila Franca de Xira–Lisbon fault zone northwards. One of these faults presents a reverse geometry apparently displacing Holocene alluvium. Vertical offsets of the Holocene sediments detected in the studied geophysical data of Porto Alto and Vila Franca de Xira–Lisbon faults imply minimum slip rates of 0.15–0.30 mm/year, three times larger than previously inferred for active faults in the Lower Tagus Valley and maximum estimates of average return periods of 2000–5000 years for M 6.5–7 co-seismic ruptures.     

Late Pleistocene highstand and recession of a small, high-altitude pluvial lake, Jakes Valley, central Great Basin, USA

Models of factors controlling late Pleistocene pluvial lake-level fluctuations in the Great Basin are evaluated by dating lake levels in Jakes Valley. “Jakes Lake” rose to a highstand at 13,870 ± 50 ¹⁴C Yr B.P., receded to a stillstand at 12,440 ± 50 ¹⁴C yr B.P., and receded steadily to desiccation thereafter. The Jakes Lake highstand is roughly coincident with highstands of lakes Bonneville, Lahontan and Russell. The rise to highstand and recession of Jakes Lake were most likely controlled by a storm track steered by the polar jet stream. The final stillstand of Jakes Lake helps constrain timing of northward retreat of the polar jet stream during the Pleistocene-Holocene transition.     

西北旅游落后现状的突破及列车旅游的新思路--兼论"西部之星"旅游列车的产品设计

近几年，西北地区的旅游业虽然取得了很大的成绩，但其发展相对于东部地区却显得落后，其主要原因之一就是西北地区的旅游资源过于分散，景点间距过大，由此导致游览行程过长，游览内容单薄，这在客观上影响了游客的选择。而与此同时，在国外，列车旅游早已作为各国旅游业的重要旅游产品为世人所熟知。文章从分析我国西北旅游业发展的现状入手，针对景点分散这一制约我国西部旅游业发展的客观不利因素，肯定了开发旅游列车产品的思路。作者以西北地区为例，结合目前我国旅游专列发展现状，提出开通“西部之星”旅游列车的构想，并进行了初步的设计。