河南省2002年夏季高温少雨成因     

李素萍  常军 《河南气象》2003,(4):5-6

从副高特征量和500hPa高度场以及高度距平场角度，分析了2002年夏季河南省气候特征，并分析了海温、太阳黑子等特征量对夏季降水的影响。结果表明：2002年夏季副热带高压偏南，北方冷空气活动偏弱，大陆暖高压强盛发展并维持，是造成河南省夏季高温少雨的直接原因；赤道中、东太平洋维持弱的暖事件和太阳活动异常以及天文背景的影响，是造成2002年河南省夏季高温少雨的间接原因。  相似文献   

四川天然气化探异常模式的研究   总被引：1，自引：0，他引：1  

姚锦琪  贾国相  颜自给  黎绍杰  阳翔  徐庆鸿 《矿产与地质》2000,(Z1)

根据四川盆地两个天然气藏的土壤地球化学异常特征、指标间的组合关系 ,建立了“环中顶”和“面状”化探异常模式。经川西地区油气化探生产实践 ,表明两种异常模式对寻找天然气藏具有良好的效果  相似文献   

A new perspective in identifying the precursory patterns of eruptions   总被引：2，自引：2，他引：0  

Laura?SandriEmail author  Warner?Marzocchi  Lucia?Zaccarelli 《Bulletin of Volcanology》2004,66(3):263-275

The complexity of the processes responsible for volcanic eruptions makes a theoretical approach to forecasting the evolution of volcanic unrest rather difficult. A feasible strategy for this purpose appears to be the identification of possible repetitive schemes (patterns) in the pre-eruptive unrest of volcanoes. Nevertheless, the limited availability and the heterogeneity of pre-eruptive data, and the objective difficulty in quantitatively recognizing complex pre-eruptive patterns, make this task very difficult. In this work we address this issue by using a pattern recognition approach applied to the seismicity recorded during 217 volcanic episodes of unrest around the world. In particular, we use two non-parametric algorithms that have proven to give satisfactory results in dealing with a small amount of data, even if not normally distributed and/or characterized by discrete or categorical values. The results show evidence of a longer period of instability in the unrest preceding an eruption, compared to isolated unrest. This might indicate, even if not necessarily, a difference in the energy of processes responsible for the two types of unrest. However, if the unrest is followed by an eruption, it seems that the seismic energy released during the unrest (parameterized by the duration of the swarm and the maximum magnitude recorded) is not indicative of the magnitude of the impending eruption. We also found that, in general, unrest followed by the largest explosive eruptions have a longer repose time than those related to moderate eruptions. This evidence supports the fact that the occurrence of a large eruption needs a sufficient amount of time after the last event in order to re-charge the feeding system and to achieve a closed-conduit regime so that a sufficiently large amount of gas can be accumulated.Editorial responsibility: T. Druitt  相似文献   

TM图像中桥梁目标识别方法的研究   总被引：18，自引：3，他引：15  

吴皓  刘政凯  张荣 《遥感学报》2003,7(6):478-484

提出了一种新的TM图像中桥梁目标的识别方法。算法充分利用了TM图像的特点,在底层处理中运用形态学的方法提取出潜在桥梁目标;在中层处理中使用链码表示目标并提取其特征参数;最后在高层处理中进行桥梁识别和一些后处理。算法识别速度快、准确率高,整个算法可以进行自动的识别,也可以有少量人工干预使得算法更稳健。实验证明该算法对于TM图像中的桥梁识别是很有效的。  相似文献   

德令哈6．6级地震前青海省前兆异常特征分析   总被引：1，自引：1，他引：0  

王培玲都昌庭  马文静 《高原地震》2003,15(3):9-14

对德令哈6．6级地震前后前兆异常用常规分析方法和部分“十五”项目的阶段性成果进行分析研究,总结了此次地震前出现的前兆异常形态及特征,探讨了此次地震与昆仑山口西8．1级地震的关系。认为,在8．1级地震的影响下,外围区域应力场调整,地壳介质变化,是此次地震前地下流体出现异常较多、分布广泛的内在原因。  相似文献   

青藏高原北部地区缺震特征及其短期预报意义     

陈玉华  张恩育 《高原地震》2003,15(2):10-16

以活动地块为单元,研究了青藏高原北部地区1985年以来的缺震异常与中强地震的对应关系,认为青藏高原北部地区缺震异常具有一定的地震预报效能,尤其是在祁连地块、柴达木地块及共和地块中的应用价值较高,可作为该区中期和短期地震预报的判据之一。多个地块同步出现缺震异常意味着某一地块6级以上地震孕育的可能。  相似文献   

Discrimination of Two Planar Structures in Directional Data     

Yehua Shan  Lianming Liu  Shenglin Peng 《Mathematical Geology》2006,38(3):375-388

For geologists, one of the common practical problems is recognization of planar structures in a directional data set. A simple case of this problem, with only two planar structures, is addressed in this paper in the light of the quartimini strategy. Its resolution turns to minimizing an objective function defined as the sum of square cross distances between each datum and the unknown normal vectors. Two distinct planar structures are recognized in a directional data set by solving iteratively for two normal vectors. Application of the proposed method to artificial and real examples demonstrates the feasibility of the method—it was both effective and fast in convergence.  相似文献   

Empirical analysis of electromagnetic profiles for groundwater prospecting in rural areas of Ibadan, southwestern Nigeria     

O. A. Ehinola  A. O. Opoola  H. A. Adesokan 《Hydrogeology Journal》2006,14(4):613-624

The Slingram electromagnetic (EM) survey using a coil separation of 60 and 100 m was carried out in ten villages in the Akinyele area of Ibadan, southwestern Nigeria to aid in the development of groundwater. Five main rock types including an undifferentiated gneiss complex (Su), biotite-garnet schist/gneiss (Bs), quartzite and quartz schist (Q), migmatized undifferentiated biotite/hornblende gneiss (M) and pegmatite/quartz vein (P) underlie the study area. A total of 31 EM profiles was made to accurately locate prospective borehole sites in the field. Four main groups with different behavioural patterns were categorized from the EM profiles. Group 1 is characterized by a high density of positive (HDP) or a high density of negative (HDN) real and imaginary curves, Group 2 by parallel real and imaginary curves intersecting with negligible amplitude (PNA), Group 3 by frequent intersection of a high density of negative minima (FHN) real and imaginary curves, and Group 4 by separate and approximately parallel (SAP) real and imaginary curves. Qualitative pictures of the overburden thickness and the extent of fracturing have been proposed from these behavioural patterns. A comparison of the borehole yield with the overburden thickness and the level of fracturing shows that the borehole yield depends more on the fracture density than on the overburden thickness. The asymmetry of the anomaly was also found to be useful in the determination of the inclination of the conductor/fracture.

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Résumé Une prospection électromagnétique Silgram (EM) utilisant une séparation de 60 et 100 m, a été réalisée sur 10 sites villageois dans la zone d’Akinyele, Ibadan, au Sud-Ouest du Nigeria, pour le développement de l’exploitation des eaux souterraines. De cette manière il a été possible de définir cinq principaux types de roches comprenant un complexe gneissique indifférencié (Su), un schiste gneissique à biotite et garnet (Bs), une quartzite et un schiste quartzitique (Q), un gneiss migmatisé à hornblende et biotite indifférenciées (M) et une veine de pegmatite et quartz recouvrant la zone d’étude. Un total de 31 profils EM a été réalisé de manière à améliorer sérieusement la localisation des forages de reconnaissance. Quatre groupes principaux ont été définis sur base de leur comportement dans les profils EM. Le Groupe 1 est caractérisé par une forte densité de courbes réelles et imaginaires, positives ou négatives (HDP ou HDN). Le Groupe 2 est caractérisé par des courbes parallèles, réelles et imaginaires, superposées à une amplitude négligeable (PNA). Le Groupe 3 rassemble les densités importantes de courbes réelles et imaginaires, d’amplitude négative minimum, fréquemment intersectées. Le Groupe 4 rassemble les courbes réelles et imaginaires, distinctes et sensiblement parallèles (SAP). Les images qualitatives de l’épaisseur de la couverture et la largeur des fractures ont pu être déterminées sur base du comportement des éléments précédemment cités. La comparaison des débits de forage, de l’épaisseur de la couche supérieure, et du degré de fracturation, montre que le débit du forage dépend plus de la densité de forage que de l’épaisseur de la couverture. L’asymétrie des anomalies a par ailleurs été très utile pour déterminer l’inclinaison des fractures conductrices.

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Resumen Se llevó a cabo un levantamiento electromagnético (EM) Slingram utilizando una separación de bobinas de 60 y 100 metros en 10 comunidades en el área Akinyele de Ibadan, suroeste de Nigeria para ayudar en el desarrollo de agua subterránea. Cinco tipos de rocas principales incluyendo un complejo de gneiss no diferenciado (Su), gneiss/esquisto de granate-biotita (Bs), cuarzita y esquisto de cuarzo (Q), gneiss de hornblenda/biotita migmatizado no diferenciado (M) y vetas de cuarzo/pegmatita (P) se encuentran en el área de estudio. Se levantaron un total de 31 perfiles EM para localizar con precisión sitios prospectivos para pozos en el campo. Se distinguieron cuatro grupos principales con diferente patrón de comportamiento a partir de los perfiles EM. El Grupo 1 se caracteriza por una alta densidad de curvas reales e imaginarias positivas (HDP) o negativas (HDN); el Grupo 2 por curvas paralelas reales e imaginarias que se interceptan con amplitud despreciable (PNA); el Grupo 3 por intersección frecuente de curvas reales e imaginarias con mínimos negativos de alta densidad (FHN); y el Grupo 4 por curvas imaginarias y reales separadas y aproximadamente paralelas (SAP). A partir de estos patrones de comportamiento se han propuesto cuadros cualitativos del espesor del material superficial y la extensión de fracturamiento. Una comparación de la productividad del pozo en relación al espesor del material superficial y el nivel de fracturamiento muestra que la productividad del pozo depende más de la densidad de fracturamiento que del espesor del material superficial. También se encontró que la asimetría de la anomalía era útil en la determinación de la inclinación de la fractura/conductor.

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Numerical subarea of sensitive zone of monitoring variable of landslides to fluctuation of water level of Three Gorges Reservoir — a case of Xietan Landslide     

ZHANG Zhen-hua  LUO Xian-qi  WU Jian  LIU Si-chun  WANG Zhi-jian 《岩土力学》2006,27(Z2):321-325

In the period of impounding and running of the Three Gorges Reservoir, the sensitive degrees of change of groundwater table and displacement to the fluctuation of water level are different in different parts of landslides induced by the fluctuation of water level (as the case of Xietan Landslide). According to the relationship between different sensitive degrees of monitoring variables (underground water level and displacement) and quantity of monitoring information, the sensitive zones of groundwater table and displacement to the fluctuation of reservoir water level are divided into different degrees by the approach of fuzzy pattern recognition. The result of numerical subarea of sensitive zone of groundwater table and displacement indicates that the middle and front part of the landslide are the main places with groundwater table affected by the fluctuation of water level of reservoir; the variation of horizontal displacement of surficial part of the middle and front part of the landslide is more sensitive to water impounding and sudden fall of water level; and with the increase of elevation and depth of the landslide, the horizontal displacement changes less and less; the change of vertical displacement of surficial parts of the landslide is most sensitive to the fluctuation of water level of Three Gorges Reservoir; and with the increase of depth, the change of vertical displacement become smaller and smaller. By the means of the numerical subarea regulation of Xietan Landslide, the suggestions to the point layout for monitoring the groundwater table and displacement in the landside of Three Gorges Reservoir are put forward.  相似文献   

Automatic picking of P and S phases using a neural tree   总被引：2，自引：1，他引：2  

S. Gentili  A. Michelini 《Journal of Seismology》2006,10(1):39-63

The large amount of digital data recorded by permanent and temporary seismic networks makes automatic analysis of seismograms and automatic wave onset time picking schemes of great importance for timely and accurate event locations. We propose a fast and efficient P- and S-wave onset time, automatic detection method based on neural networks. The neural networks adopted here are particular neural trees, called IUANT2, characterized by a high generalization capability. Comparison between neural network automatic onset picking and standard, manual methods, shows that the technique presented here is generally robust and that it is capable to correctly identify phase-types while providing estimates of their accuracies. In addition, the automatic post processing method applied here can remove the ambiguity deriving from the incorrect association of events occurring closely in time. We have tested the methodology against standard STA/LTA phase picks and found that this neural approach performs better especially for low signal-to-noise ratios. We adopt the recall, precision and accuracy estimators to appraise objectively the results and compare them with those obtained with other methodologies.Tests of the proposed method are presented for 342 earthquakes recorded by 23 different stations (about 5000 traces). Our results show that the distribution of the differences between manual and automatic picking has a standard deviation of 0.064 s and 0.11 s for the P and the S waves, respectively. Our results show also that the number of false alarms deriving from incorrect detection is small and, thus, that the method is inherently robust.This paper has not been submitted elsewhere in identical or similar form, nor will it be during the first three months after its submission to Journal of Seismology.  相似文献