新疆乌鲁木齐地区多年水氡观测资料的统计与分析

通过对乌鲁木齐地区1980—7．001年的水氡观测资料进行全时域扫描分析，以乌鲁木齐为中心300km范围内Ms≥5．0的地震事件为研究对象，挑选出观测资料中异常时段，用地震预报效能评价评分的方法对水氡观测资料预报地震的能力进行评价。     

Explosion seismic reflections from the Earth’s core

Recent seismological studies have presented evidence for the existence of a layer with ultra-low seismic velocities at the core-mantle boundary at ca. 2900 km depth. We report high-amplitude, high-frequency, and laterally coherent seismic arrivals from three nuclear explosions in Siberia. With recording station intervals of 15 km, the seismic phases are readily correlated and show the presence of a thin, ultra-low velocity zone in a region where it was not previously reported. The duration and complexity of the arrivals are inconsistent with a simple core-mantle boundary and require a hitherto unidentified, kilometre-scale, fine structure in the ultra-low velocity zone. The observations may be explained by a ca. 7 km thick, two-layer, ultra-low velocity zone with exceptional low velocities, which indicate the presence of high percentages of melt (>15%), in particular in the lower part of the zone. Waveform variation implies lateral change in the thickness and physical properties of the ultra-low velocity zone with a wavelength of less than 100 km.     

叶面积指数(LAI)的遥感定量方法综述

总结了当前遥感定量研究叶面积指数(LAI)的两种主要方法:统计模型法和光学模型法,阐述了各自的机理和研究进展,在此基础上,讨论了两种方法的优缺点及未来的发展趋势。     

A millennial-scale record of Holocene tsunamis on the Kronotskiy Bay coast, Kamchatka, Russia

Deposits from as many as 50 large tsunamis during the last 7000 years are preserved on the Pacific coast of the Kamchatka Peninsula near the mouth of the Zhupanova River, southern Kronotskiy Bay. These deposits are dated and correlated using Holocene marker tephra layers. The combined, preserved record of tsunami deposits and of numerous marker tephras on Kamchatka offers an unprecedented opportunity to study tsunami frequency. For example, from the stratigraphy along southern Kronotskiy Bay, we estimate frequency of large tsunamis (>5 m runup). In the last 3000 years, the minimum frequency is about one large tsunami per 100 years, and the maximum about one large tsunami per 30 years; the latter frequency occurred from about 0 to 1000 A.D. This time interval corresponds to a period of increased seismicity and volcanic activity that appears to be recorded in many places on the Kamchatka Peninsula.     

河南降水及最长连续无降水日数时空特征

利用河南省均匀分布的50个台站自建站至1997年近50年的定时降水资料，分析了河南省日小雨、日中雨、日大雨降水过程出现次数和最长连续无降水日数，结果显示，河南省日小雨、日中雨降水过程一年四季均可出现，日大而过程主要出现在3～11月份，冬季仅在豫南一些台站出现，各级降水过程出现次数季节性变化明显，冬季出现最少，夏季出现最多，其地理分布随测站纬度、拔海高度、地形地貌不同有较大差异；最长连续无降水日数也有明显的季节性变化特点，其最大值多出现在冬季，春秋次之，夏季最小，地理位置差异也较明显。     

地表非均匀性对区域平均水分通量参数化的影响

次网格尺度地表非均匀性对于网格区平均通量具有重要影响。若将网格区视为均一地表 ,并不能真实描述地 气通量交换过程 ,且可造成很大误差。文中从理论上证明 ,区域平均水分通量的变化率可分解为两部分 :第一部分为区域水分通量的算术平均变化率 ;第二部分为非均匀性所引起的水分通量变化率扰动 ,它与区域内土壤水分空间分布的变差系数有关。数值试验表明 ,地表土壤水分的水平空间变差系数集中反映了区域内土壤水分分布的非均匀程度 ,不同土壤对同样的非均匀程度其敏感性是不同的。变差系数愈大 ,非均匀性愈强 ,在相同的土壤水分平均值下 ,不同土壤类型对地表非均匀程度的敏感性并不相同。例如沙土和粘土受非均匀性的影响就可相差数十倍。     

DOES WIND STRESS DEPEND ON SEA-STATE OR NOT? – A STATISTICAL ERROR ANALYSIS OF HEXMAX DATA

There have been several claims, either explicit or by implication, either based on experimental evidence or on theoretical reasoning, that the wind stress is modified by the stage of development of the wind sea. However, the overall evidence is weak, because theories are still incomplete and because it is questionable whether the sea-state effect, which is of the order of 10%, can be separated from experimental noise, which is of the order of 20%. In this paper a rigorous statistical analysis of HEXMAX data is pursued in order to establish the significance of sea-state effects. It appears that the enhanced drag, especially at high winds, which has already been established by previous analyses, cannot be attributed to the effect of young waves. The analysis provides no clues for the actual mechanism, which could be related to breaking or shoaling waves. As the effect of sea-state on wind stress is much smaller than the experimental noise level, it is hard to detect. Nevertheless, HEXMAX seems to contain a wave effect that is at the edge of statistical significance. It is, however, not the wave age itself that influences the drag, but a parameter involving wave height.Because the HEXMAX evidence is only indicative, we conclude that the issue set out in this paper cannot be answered on the basis of the HEXMAX data alone. It is recommended that error analyses are also carried out for other relevant observational data sets and that new measurements with suppressed noise will be taken up.     

The mechanisms of shallow earthquakes and the monitoring of a comprehensive test ban

The ability of seismological criteria to identify earthquakes from underground explosions depends partly on the orientation of the earthquake source. Well-determined double-couple moment tensor solutions for a large number of earthquakes have been published in the Harvard centroid moment tensor (CMT) and United Slates Geological Survey (USGS) catalogues. Statistical analyses of these catalogues indicate that the distribution of the orientation of earthquake mechanisms is not random. The distribution of the T axes shows significant clustering around the downward vertical, indicating that a larger number of earthquake mechanisms radiate compressional P -wave energy to teleseismic distances from near the maximum of the radiation pattern than is predicted if earthquake sources are randomly oriented double couples. The clustered T axes correspond to compressional dip-slip mechanisms, and it is this type of mechanism which is believed to cause both the m _b: M _s (the ratio of body-wave to surface-wave magnitude) and first-motion criteria to misidentify an earthquake as an explosion.