重磁异常的人机联作校正－迭代反演

本文提出了三度体重磁异常的人机联作校正－迭代反演方法。该方法用二度半组合多边形棱柱体来逼近三度体，从而把三度体重磁异常反演问题转化为二度半体的反演问题；为了消除组合体迭加场的影响，该方法采用了一种校正－迭代技术。理论模型反演计算表明，该方法实际可行。     

Study of the characteristics of earthquake precursory anomalies of He and H2 Beijing No. 2 Cotton Mill well and their relation with earthquakes

This paper systematically summarized the relation of the abnormal change of He and H₂ dissolved gasses in deep hot-water well at Beijing No. 2 Cotton Mill and their relation with seismicity of the region. An empirical formula for the relation of the precursory anomaly of He and H₂ gasses with the magnitude and occurrence time of earthquake has been derived. Two events of magnitude greater than 5 in North China had been successfully predicted by using this formula. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 490–497, 1993.     

Parabolic density function in sedimentary basin modelling

For modelling sedimentary basins of large thickness from their gravity anomalies, the concept of parabolic density function which explains the variation of true density contrast of the sediments with depth in such basins is introduced inBott's (1960) procedure. The analytical expression the gravity anomaly of a two-dimensional vertical prism with parabolic density contrast needed to estimate the gravity effect of the basin in modelling procedure is derived in a closed form. Two profiles of gravity anomalies, one across San Jacinto Graben, California and the other across Tucson basin, Arizona where the density of sediments is found to vary with depth are interpreted.     

云南水汞在连发地震前短临异常及震后变化特征

通过对1995年5月6日—1996年2月3日发生在云南境内及其中缅边境一带的4组5次M≥6．0级强震的研究,发现水汞在强震连发期都出现短临异常及震后变化;与2001年云南省内6组7次5．0—5．9级中强地震短临异常及震后变化进行比较,结果表明强震连发期水汞的短临异常特征表现为异常台站多、异常幅度大、异常范围广和多台站水汞在异常中发震。中强震连发期水汞的短临异常特征与此相反。表现为异常台站少、异常幅度小、异常范围小和多台站水汞在异常结束后发震。     

试论中国重要景观区区域地球化学异常系统评价的量化模型

在对中国5个重要景观区1:20万金、铜表生地球化学异常特征进行总结、对比,并讨论景观、表生因素对区域异常评价标志影响的基础上,进一步充实、完善了区域异常系统评价体系的思路和评价准则,提出了区域地球化学异常系统评价的量化模型。     

青藏高原区域重磁异常的东西向分区及其构造地质特征

自从大陆整合以来作为一个整体的青藏高原继续受着印度板块向北俯冲的影响,也必定不断地改造着原各地体的结构构造,形成了高原整体意义上东西向的差异。这种差异与原本各地体的组成、结构和东西向延伸不一致。这不仅表现在南北向断裂构造跨各单个地体范围的出现,而且,逐步形成了东西的分区。这种分区突出地表现在区域重力与磁场的特征上,这不仅是局部的岩石磁性与密度变化的结果,而且是由于印度板块向北俯冲过程中,在其前缘的不同部位上经受的压力不同,以及地块的隆升与扩张作用的差异造成了高原东西各区段的地壳组分与厚度的变化。青藏高原的南北向断裂构造并非地壳上层的局部断裂,它具有深层的原因。由于印度板块向北推进的过程中不是均匀地齐头并进,而是在帕米尔高原以东的青藏高原范围内存在着推进速度和俯冲深度的差异,随着高原隆升的加剧高原本身出现断裂,自中新生代以来就存在着一定差异,所以南北向的断裂构造比目前地表见到的多些,而且具有较大的深度,Moho面的深度和地壳厚度都受南北向断裂的控制,并形成了区域重磁场的变化。同时,高原的东西向拉张作用也使南北断裂带发育加剧。     

RELATION BETWEEN SUMMER TYPHOON FREQUENCY ANOMALIES IN WEST PACIFIC AND ENSO EVENTS AND THE ANOMALOUS ATMOSPHERIC CIRCULATION CHARACTERISTICS

By using data of serially numbered typhoons in northwestern Pacific and NOAA OLR data and NCEP/NCAR reanalysis data of wind field, based on the statistics and study of the relationship between the calendar years with more (or fewer) summer typhoons and ENSO events, we compared the composites of OLR eigenvectors and tropical summer wind fields during El Nino and La Nina events with more or fewer than normal summer typhoons, respectively. The results show that, in summer, without remarkable systematic anomalies of Mascarene High and Australia High in South Hemisphere, the anomaly of Walker circulation will dominate and follow the rule of ENSO impacts to atmospheric circulation and typhoon frequency. Otherwise, when systematic anomalies of Australia High appear during the El Nino events, circulation anomalies in the South Hemisphere will dominate, and many more typhoons will occur. In 1999, which is a special year of La Nina events, northward and eastward monsoon was induced by the stronger Mascarene High, and fewer typhoons arose. The typhoon source are regions where weak vertical wind shear, warm pool in western Pacific and the area with monsoon troughs are overlapping with each other. Finally, this paper analyzes and compares the source locations and ranges of more (fewer) typhoons in the events of El Nino and La Nina, respectively.     

北祁连西段熬油沟及卡洼沟一带Au、Pt、Pd异常特征及找矿方向

北祁连西段作为甘肃一个重要的多金属成矿带，随着地质找矿工作不断地加强，日渐重要。根据熬油沟及卡洼沟一带水系沉积物、岩屑和岩石剖面测量结果，对Au、Pt、Pd和Pb、Zn等成矿元素的分布特征和组合关系进行了分析，总结了该处成矿地质背景和地球化学异常特征，指出了找矿方向。     

纳米级微粒地球化学测量中异常重现性研究

纳米级微粒测量是寻找隐伏矿的新方法,选取实地模拟实验和在已知隐伏矿区,利用液态捕集剂和等离子体质谱分析测试样品,进行重复测量试验,研究结果表明,不同成矿元素,在地表形成异常的运移富集速率不同,其运移速率主要取决于纳米级微粒本身的地球化学性质,地下上升气流、断裂等裂隙有利于微粒的上升运移富集;纳米级微粒地球化学重复测量时,异常可具有良好的重现性,但异常重现较常规气体缓慢,通常需要2~3个月。     

Crustal attenuation in the Southern Andean retroarc (38°–39°30′ S) determined from tectonic and gravimetric studies: The Lonco-Luán asthenospheric anomaly

The western retroarc of the Southern Andes between 38° and 40° S is formed by a NNW-elongated ridge not associated with stacked thrust sheets. On the contrary, during the last 4–3 Ma this ridge was affected by extensional deformation, regional uplift and related folding on a very broad scale. Receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust. Expected crustal thickness at these latitudes is around 38 km, whereas in this part of the retroarc the thickness is less than 32 km. The causes for such attenuation have been linked to a moderate steepening of the subducted Nazca plate beneath the South American plate, which is suggested by a westward shift and narrowing of the magmatic arc during the last 4 to 5 Ma. Gravimetric studies show that the upper plate did not react homogeneously to slab steepening, but ancient sutures and lithospheric discontinuities deeply buried under Mesozoic to Cenozoic sequences in the retroarc were locally reactivated. These processes resulted in an asthenospheric anomaly that correlates at the surface with the area of Pliocene to Quaternary doming, widespread extension and three radial troughs. Two of the troughs have accommodated substantial amounts of extension, but the third was probably aborted at an early stage. Moreover, the presence of an anomalous concentration of calderas and large volcanic centers over the proposed asthenospheric anomaly, and their age distribution, may indicate minor migration of the asthenospheric anomaly between 4 and 2 Ma through the western South American plate.