伽师强震群活动过程中喀什台地磁加卸载响应比变化特征研究     

史勇军  孙燕萍  朱燕  范素琴  巴克·买买提  热汗古·衣明克力木 《内陆地震》2002,16(1):84-88

应用地磁响应比方法 ,分析计算了喀什地磁台 1996— 1999年地磁资料 ,结果表明在伽师强震前地磁场有明显的异常 ,这为震磁信息提取和异常判断提供了依据  相似文献   

具有时变参数的门限自回归模型及其在气候预报中的应用   总被引：2，自引：0，他引：2  

杨明  张万诚  沙文生 《热带气象学报》1996,12(3):224-229

将时变参数模型引入门限自回归模型中，提出具有时变参数的门限自回归模型，并对昆明，蒙自，河口等地区３月温度序列进行预报，结果表明：这种模型比门限自回归模型的预报准确度有明显提高，这是因为用这种模型进行预报时，可以随时更新预报模式。  相似文献   

FORMULAS FOR INCIPIENT MOTION OF MUD WITH VARIOUS DENSITIES     

YANG Meiqing  WANG Cuiling 《国际泥沙研究》1996,(1)

ＦＯＲＭＵＬＡＳＦＯＲＩＮＣＩＰＩＥＮＴＭＯＴＩＯＮＯＦＭＵＤＷＩＴＨＶＡＲＩＯＵＳＤＥＮＳＩＴＩＥＳＹＡＮＧＭｅｉｑｉｎｇａｎｄＷＡＮＧＣｕｉｌｉｎｇＡｂｓｔｒａｃｔ：Ｍｕｄｆｏｒｍｅｄｆｒｏｍｆｉｎｅｃｏｈｅｓｉｖｅｓｅｄｉｍｅｎｔｓｃａｎｈａｖ...  相似文献   

沙土含水率对起沙临界风速影响   总被引：3，自引：5，他引：3  

包为民 《中国沙漠》1996,16(3):315-318

根据重力、凝聚力与拖曳力的力矩平衡关系，推导出起沙临界风速与粒径和沙土含水率的关系，并分析了含水率对起沙临界风速的定量作用  相似文献   

Jason-2卫星阈值重跟踪算法比较     

范雕  李姗姗  孟书宇  曲政豪  刘帆  冯进凯 《测绘科学技术学报》2017,34(2)

选取Jason-2卫星在中国南海北纬15°~18.5°范围1 276个波形数据,依据Threshold算法和SeaIce算法对波形进行重跟踪,得到不同阈值水平下的距离改正结果。结果表明:当星下点轨迹靠近陆地时,距离改正值增大。然后,依据不同方法、不同阈值水平对应的距离改正值对卫星观测的海面高实施修正,得到相应的海面高结果。作为验证,选取法国国家太空研究中心(CNES)发布的海面高作为外部检核条件。将修正后的海面高与CNES公布的海面高进行较差比较,较差值的统计分析表明:SeaIce重跟踪算法在阈值水平为50%时,差值的标准差明显小于其他方法的计算结果。  相似文献   

The rainfall intensity–duration control of shallow landslides and debris flows: an update     

Fausto Guzzetti  Silvia Peruccacci  Mauro Rossi  Colin P. Stark 《Landslides》2008,5(1):3-17

A global database of 2,626 rainfall events that have resulted in shallow landslides and debris flows was compiled through a thorough literature search. The rainfall and landslide information was used to update the dependency of the minimum level of rainfall duration and intensity likely to result in shallow landslides and debris flows established by Nel Caine in 1980. The rainfall intensity–duration (ID) values were plotted in logarithmic coordinates, and it was established that with increased rainfall duration, the minimum average intensity likely to trigger shallow slope failures decreases linearly, in the range of durations from 10 min to 35 days. The minimum ID for the possible initiation of shallow landslides and debris flows was determined. The threshold curve was obtained from the rainfall data using an objective statistical technique. To cope with differences in the intensity and duration of rainfall likely to result in shallow slope failures in different climatic regions, the rainfall information was normalized to the mean annual precipitation and the rainy-day normal. Climate information was obtained from the global climate dataset compiled by the Climate Research Unit of the East Anglia University. The obtained global ID thresholds are significantly lower than the threshold proposed by Caine (Geogr Ann A 62:23–27, 1980), and lower than other global thresholds proposed in the literature. The new global ID thresholds can be used in a worldwide operational landslide warning system based on global precipitation measurements where local and regional thresholds are not available..  相似文献   

利用门限自回归建模预测广东地区2000年前后的地震强度     

刘特培 《华南地震》1998,18(3):41-45

利用自激励门限自回归建模的原理和方法,对广东地区陆地和珠江口外以及台湾海峡部分地区２０００年前后的最大地震强度进行了预测。结果表明,该区至２００１年可能发生地震的最大震级为ＭＬ５．２级,未来几年内发生Ｍ≥６．０级地震的可能性较小。  相似文献   

These lit areas are undeveloped: Delimiting China’s urban extents from thresholded nighttime light imagery     

《International Journal of Applied Earth Observation and Geoinformation》2016

Nighttime light imagery is a powerful tool to study urbanization because it can provide a uniform metric, lit area, to delimit urban extents. However, lit area is much larger than actual urban area, so thresholds of digital number (DN) values are usually needed to reduce the lit area. The threshold varies greatly among different regions, but at present it is still not very clear what factors impact the changes of the threshold. In this study, urban extent by province for China is mapped using official statistical data and four intercalibrated and geometrically corrected nighttime light images between 2004 and 2010. Lit area in the imagery for most provinces is at least 94% greater than the official amount of urban area. Regression analyses show a significant correlation between optimal thresholds and GDP per capita, and larger thresholds more commonly indicate higher economic level. Size and environmental condition may explain a province’s threshold that is disproportionate to GDP. Findings indicate one threshold DN is not appropriate for multiple (adjacent) province urban extent mapping, and optimal thresholds for one year may be notably different than the next. Province-level derived thresholds are not appropriate for other geographic levels. Brightness of nighttime lights is an advantage over imagery that relies on daylight reflection, and decreases in brightness indicate faster growth in the horizontal direction than the vertical. A province’s optimal threshold does not always maintain an increase with population and economic growth. In the economically developed eastern provinces, urban population densities decreased (and this is seen in the brightness data), while urban population increased.  相似文献   

2000年前辽宁地区地震活动趋势预测     

Sun Wenfu Gu Haoding 《东北地震研究》1995,(3)

根据数理统计理论和有关文献，利用辽宁地区（３８．７°－４３°Ｎ，１１９°－１２５°Ｅ）１９７０年以来的地震资料，建立了逐年最高震级时间序列的门限自回归模型和修改的震级一频度关系。同时，对辽宁地区地震活动的时空分布特征也作了详细的研究。最后，对辽宁地区未来（到２０００年）地震活动趋势和强度作了预测。  相似文献   

Threshold of coarse sediment transport in broad and narrow natural streams     

P. A. Carling 《地球表面变化过程与地形》1983,8(1):1-18

The threshold of coarse sediment transport has been examined in natural streambeds in an upland Pennine (U.K.) area. Threshold values of the total boundary shear stress (T₀) (for a given grain size), in a narrow natural stream (W/D < 11) are considerably higher than values of T₀ in a broad stream (W/D > 11). Efficiency in the entrainment process is related not only to the overall channel geometry, but also varies as a function of discharge in channels characterized by compound roughness. Empirical curves relating T₀ and a mean grain size (d ₅) are presented, but are limited in application to streams of similar physical and hydraulic characteristics as the ones examined in this investigation. Considerable divergence is noted between these empirical functions and a summary empirical function for general application obtained from a published source. The reasons for this divergence are discussed. The influence of grain shape was found not to be important in the initiation of motion criterion. This conclusion may reflect the limited range of natural grain shapes in the study streams, but might reasonably apply to other field investigations of similar streams. Modifications of the Shields' and Yalin diagrams are suggested for practical applications in shallow streams with poorly-graded bed material. The Shields' parameter may be regarded as an inverse function of the relative protrusion of individual grains in the shallow flow depth (d ₅/D). The increased importance of augmented drag forces, in the entrainment process in shallow flows, is suggested as the physical explanation for the reduced values of the Shields' parameter. However, the relationships presented should not be applied to laboratory experiments concerned with well-graded sediments (therefore beds with little deviation in level), in which the Shields' parameter may be regarded as constant at high Reynolds' grain numbers. Consistent estimated field values of ?, a threshold sediment transport parameter, might be used to compare field data to threshold values derived from statistical arguments and laboratory experiments reported in the literature.  相似文献