1997年广东台山小震群特征

分析了１９９７年１１～１２月在广东台山市三合镇附近发生的最大震级为４１级小震群的活动特征、地质构造背景和震源机制解,并将其与１９７０年７～１２月发生的最大震级为４０级的台山震群进行了对比,计算了两次小震群的序列特征参数,结果表明,１９９７年震群具有前兆震群的某些特征。     

Vertical accuracy evaluation of freely available latest high-resolution (30 m) global digital elevation models over Cameroon (Central Africa) with GPS/leveling ground control points.

Digital Elevation Models (DEMs) contain topographic relief data that are vital for many geoscience applications. This study relies on the vertical accuracy of publicly available latest high-resolution (30?m) global DEMs over Cameroon. These models are (1) the ALOS World 3D-30?m (AW3D30), (2) the Shuttle Radar Topography Mission 1 Arc-Second C-Band Global DEM (SRTM 1) and (3) the Advanced Spaceborne Thermal Emission and Reflection Global DEM Version 2 (ASTER GDEM 2). After matching their coordinate systems and datums, the horizontal positional accuracy evaluation was carried out and it shows that geolocation errors significantly influence the vertical accuracy of global DEMs. After this, the three models are compared among them, in order to access random and systematic effects in the elevation data each of them contains. Further, heights from 555 GPS/leveling points distributed all over Cameroon are compared to each DEM, for their vertical accuracy determination. Traditional and robust statistical measures, normality test, outlier detection and removal were used to describe the vertical quality of the DEMs. The test of the normality rejected the hypothesis of normal distribution for all tested global DEMs. Overall vertical accuracies obtained for the three models after georeferencing and gross error removal in terms of Root Mean Square (RMS) and Normalized Median Absolute Deviation (NMAD) are: AW3D30 (13.06?m and 7.75?m), SRTM 1 (13.25?m and 7.41?m) and ASTER GDEM 2 (18.87?m and 13.30?m). Other accuracy measures (MED, 68.3% quantile, 95% quantile) supply some evidence of the good quality of AW3D30 over Cameroon. Further, the effect of land cover and slope on DEM vertical accuracy was also analyzed. All models have proved to be worse in the areas dominated by forests and shrubs areas. SRTM 1 and AW3D30 are more resilient to the effects of the scattering objects respectively in forests and cultivated areas. The dependency of DEMs accuracy on the terrain roughness is evident. In all slope intervals, AW3D30 is performing better than SRTM 1 and ASTER GDEM 2 over Cameroon. AW3D30 is more representative of the external topography over Cameroon in comparison with two others datasets and SRTM 1 can be a serious alternative to AW3D30 for a range of DEM applications in Cameroon.     

湖南省桃江-城步断裂带北东段锑矿成矿规律及找矿模型

桃江-城步断裂带是湘中"拗拉槽"中主要复活断裂之一,由于多期复活,因此具有规模大、切割深、控岩控矿明显的特点,为湘中地区重要的控矿断裂带.北东段即指南西自安化廖家坪,北东至桃江板溪的走向长度约40 km的地段,该段主要切割了雪峰期及加里东期两个构造层,并有中-大型规模脉状锑矿产出,而正是这些脉状锑矿逐渐改变湘中锑矿储量的比例,通过对该锑矿类型、特征、控矿构造组合型式、锑矿成矿规律、成矿-找矿模型的研究,提出了新的认识,并根据所建模型预测了大福坪锑矿和廖家坪金矿,经验证分别达到了中型及大型规模.