青藏块体东北缘中强地震前小震频度异常研究   总被引：3，自引：0，他引：3  

冯建刚  周龙泉  杨立明  代炜 《地震》2009,29(3):19-26

1980年以来青藏块体东北缘共发生26次M_S5.0以上地震,其中22次在时间和空间上相对独立。 通过系统研究这22次中强地震前其邻区小震活动的增强现象,发现有17次中强地震前存在比较明显的小震增强现象。 虽然小震增强现象在多数中强地震前存在,但是利用小震活动的增强对未来中强地震的预测比较困难。 文中结合青藏块体东北缘小震活动的特点,尝试提出根据小震活动空间格局是否改变统计小震频度的方法,并且进行了初步的应用。 结果表明: 利用新方法统计小震的频度更能突出中强地震前的小震频度异常,并且中强地震前的小震频度异常幅度受空间范围大小的影响不大,能够有效的提取青藏块体东北缘中强地震前的中短期异常指标。  相似文献   

小旋转椭球粒子群的微波衰减系数与雷达反射率因子之间的关系   总被引：6，自引：1，他引：5  

王振会  张培昌 《气象学报》2000,58(1):123-128

通过模拟及取样导出了小旋转椭球粒子群旋转轴呈 3种不同取向 ,而入射电磁波分别为水平发射水平偏振波及水平发射垂直偏振波时的衰减系数与雷达反射率因子之间的关系 ,获得 3种波长的具体表达式 ,并对结果作了物理分析。所得结果可直接用于雷达定量测量降水时的衰减订正。  相似文献   

LANDFORM MORPHOLOGIC RELATIONS BETWEEN INTER-GULLIED AND GULLIED LAND AREAS--A CASE STUDY OF THE WANGJIAGOU WATERSHED IN THE WEST OF SHANXI PROVINCE     

Hao CHEN  Hai-yan FANG  Qiang-guo CAI  Guang-lin LIANG  Zong-qi YUE 《国际泥沙研究》2006,21(1)

Previous studies on erosional relations between inter-gullied and gullied lands have mainly concentrated on exploration of water and sediment relations, with few quantitative studies of evolution relations between inter-gullied land and gullied landform erosion in small catchments. This paper, using information from a 1:5000 digital orthophotomap (DOM), digital elevation model(DEM), and topographic map of the same period and of the same scale, quantitatively analyzes the impact and interactions of inter-gullied and gullied land geomorphologic characteristics on the dissected extent of a catchment using orthogonal polynomial regression analysis. Results indicate that gullies play a leading role in the catchment morphologic evolution and extent of cracked ground surface. When inter-gullied land areas are the same, a 0. 1 km2 gullied land area has the maximum effect on the erosive evolution intensity of the catchment cracked degree. The smaller the catchment area is, the greater the extent of cracked ground surface and gully intensity would be. The geomorphologic evolution mechanism of gullied catchments can be explained as a function of geomorphologic indicators of inter-gullied and gullied land characteristics.  相似文献   

浅谈有强降水时小型蒸发器加盖的意义     

林梅香 《气象研究与应用》2006,27(2):58-58

通过对有强降水时,小型蒸发器在加盖和不加盖两种不同情况下蒸发量的对比,说明加盖的意义。  相似文献   

0920号超强台风“卢碧”引起的强海上大气波导成因分析与数值模拟研究   总被引：2，自引：1，他引：1  

胡昊  费建芳  丁菊丽  王挺  黄小刚  程小平  袁炳 《气象学报》2018,76(4):620-634

基于中国台湾地区主持的侵台台风之飞机侦察及下投式探空仪观测实验（Dropwindsonde Observations for Typhoon Surveillance near the Taiwan Region,DOTSTAR）获得的高分辨率下投式探空仪探测资料,分析了2003年9月—2012年8月所有发生在中国台湾地区附近海域的台风型大气波导事件,遴选出一次由0920号超强台风“卢碧”引起的强台风型海上大气波导过程作为研究对象。利用欧洲中期数值预报中心（ECMWF）再分析资料（水平分辨率0.125°×0.125°）,对此次波导的生成原因进行了分析;基于WRF模式比较了不同初始化方法对台风强度、尺度和周围台风型大气波导的模拟能力。结果表明,此次强台风型大气波导发生在台风环流西北侧外围的弱下沉运动区,其形成与850 hPa高度附近北方强干空气平流导致湿度随高度锐减密切相关。在数值模拟中运用台风动力初始化方法,可以有效改进台风强度、路径和尺度的模拟效果,进而有利于改善台风型大气波导尤其是波导层所在高度的模拟效果。台风外围出现的大气波导通常以悬空波导为主,模拟效果与台风螺旋雨带和内核尺度的模拟关系密切,而与台风强度和眼墙结构关系不大。中尺度数值模式WRF具有模拟台风型大气波导的能力,是研究台风型大气波导的有力手段。   相似文献   

Source parameters of the M_L 4.1 earthquake of November 08, 2006, southeast Beni-Suef, northern Egypt     

A. Badawy  A.K. Abdel-Fattah  Sh. M. Ali  W. Farid 《Journal of African Earth Sciences》2008,51(3):151-159

In the early morning hours on Wednesday November 08, 2006 at 04:32:10(GMT) a small earthquake of M_L 4.1 has occurred at southeast Beni-Suef, approximately 160 km SEE of Cairo, northern Egypt. The quake has been felt as far as Cairo and its surroundings while no casualties were reported. The instrumental epicentre is located at 28.57°N and 31.55°E. Seismic moment is 1.76 E14 Nm, corresponding to a moment magnitude M_w 3.5. Following a Brune model, the source radius is 0.3 km with an average dislocation of 1.8 cm and a 2.4 MPa stress drop. The source mechanism from a first motion fault plane solution shows a left-lateral strike-slip mechanism with a minor dip-slip component along fault NNW striking at 161°, dipping 52° to the west and rake −5°. Trend and plunging of the maximum and minimum principle axes P/T are 125°, 28°, 21°, and 23°, respectively. A comparison with the mechanism of the October, 1999 event shows similarities in faulting type and orientation of nodal planes.Eight small earthquakes (3.0  M_L < 5.0) were also recorded by the Egyptian National Seismological Network (ENSN) from the same region. We estimate the source parameters and fault mechanism solutions (FMS) for these earthquakes using displacement spectra and P-wave polarities, respectively. The obtained source parameters including seismic moments of 4.9 × 10¹²–5.04 × 10¹⁵ Nm, stress drops of 0.2–4.9 MPa and relative displacement of 0.1–9.1 cm. The azimuths of T-axes determined from FMS are oriented in NNE–SSW direction. This direction is consistent with the present-day stress field in Egypt and the last phase of stress field changes in the Late Pleistocene, as well as with recent GPS measurements.  相似文献   

Petrography and geochemical characteristics of the sediments of the small River Hemavati, Southern India: Implications for provenance and weathering processes   总被引：2，自引：0，他引：2  

S. Sensarma  V. Rajamani  Jayant K. Tripathi 《Sedimentary Geology》2008,205(3-4):111-125

Small rivers (≤ 100 km length) are likely to drain fewer rock types. Therefore, their solutes and sediments are good indicators of weathering environments typical of their basins and help constraining the nature of their source rocks. To understand this, the texture, mineralogy, major and trace element compositions of the sediments deposited by the River Hemavati, a northern upland tributary of the Cauvery River in southern India, are analyzed and discussed.

The Hemavati sediments are overall of fine sand size (mean 2–3), and have high concentrations of FeO (≤ 7 wt.%), TiO₂ (≤ 1.2 wt.%), Cr (≤ 350 ppm) and Ni (≤ 125 ppm). Major and trace element distribution call for a binary source for the sediments, and particularly point to contrasting climatic conditions of their provenances. The source areas in the upstream and downstream parts are exposed to sub-humid high relief and sub-arid low relief conditions, respectively, with distinct weathering characteristics. The CIA values (85–48) decrease from near the source to downstream, suggesting that the downstream rain-shadow part of the catchment suffered only minor chemical weathering.

On the other hand, the REE distribution in the Hemavati sediments indicates contrasting lithologies in their provenance, and is not controlled by chemical weathering. On the basis of REE patterns, the sediments are divided into two compositional groups. The Type 1 sediments have a REE chemistry similar to the upper continental crust, and have been derived from the > 3.2 Ga composite peninsular gneisses occurring in the low-lying, semi-arid Mysore Plateau. The Type 2 sediments, however, have dominantly intermediate to mafic granulite contributions from the tectonically uplifted Western Ghats, weathered under sub-humid conditions. High concentrations of FeO, TiO₂, Cr and Ni in the sediments suggest mafic-dominated source lithologies in the upper catchment, a feature also confirmed by field observations and petrographic study.  相似文献   

不同震级范围的地震频度和频度比     

蔡静观  吴惠芝 《地震地磁观测与研究》1992,(6)

讨论了云南地区不同震级范围的小震频度在强震前的时间进程曲线,发现在介质比较破碎地区,震级偏小的地震频度显示出较明显的强震前孕震系统的非线性阶段,而在介质比较完整的地区,则震级偏大的地震频度反应较明显。为此,引入了频度比的概念,结果表明,强震孕震区的频度比表现为在强震前2—4年,持续增加或持续降低,在强震前1—2年,呈(增加后)降低或(降低后)增加的异常变化,曲线形态出现拐点。对频度比在实际预报工作中的预报能力,也进行了讨  相似文献   

High flow events and sediment transport in small streams in the ‘tertiary basin’ area in piedmont (Northwest Italy)     

Domenico Tropeano 《地球表面变化过程与地形》1991,16(4):323-339

Rainfall, peak discharges, and suspended sediment transport were surveyed for 280 events in three small (0.8 to 10 km²) catchments in a hilly area derived from Neogene marls, silts, and sands. Under similar hydrological input conditions, stream flow behaviour and sediment delivery differed considerably from one catchment to another, depending on topography, lithology, land use, and especially sediment availability. Analytical treatment of data showed a good fit between sediment yield and peak flow discharge. Less good, although still significant, was the correlation between sediment concentration and discharge values for different flow stages. Rainfall peak/basin lag time and rainfall/discharge showed poor or no correlation, mainly due to strong variations in rainfall distribution. Sediment concentration in the catchments varied enormously according to season, from zero up to 334 g 1^?1; sediment yield was 160-900 tonnes km^?2 yr^?1 in the two major catchments, and over 5200 tonnes km^?2 yr^?1 in the headwater catchment, stressing the importance of small tributaries not only in inducing floods in downstream channels, but also in sediment supply.  相似文献   

Rotating flow past a short,sliced cylinder at finite Rossby number     

K. A. Polzin  M. Angelats I Coll  M. R. Foster 《地球物理与天体物理流体动力学》2013,107(1-2):67-103

Abstract

Flow past a short obstacle in a rotating reference frame generates a wake that is crucial to the overall flow structure if the Rossby number is of the order of the quarter power of the Ekman number. We present here a theory for such flows for the case when the obstacle's top is an oblique, planar surface. The results arise from a combination of asymptotic analysis and numerical computation, and show that even weak asymmetry generates significant global effect on the entire flow-field. Comparisons with the experiments reported by Foster and Davies (1996) are generally good when the high edge is at 90° to the oncoming flow.  相似文献