Investigation of rupture process of the 1999 M =5.4 Xiuyan, Liaoning, earthquake sequence

Conclusions The sequence of the November 29, 1999 Xiuyan, Liaoning, earthquake withM _S=5.4 is relocated, and its rupture process is analyzed. Results are as follows: The rupture extended mainly before the January 12, 2000,M _S=5.1 earthquake. There are two phases of rupture extending: The first phase was before the November 29, 1999,M _S=5.4 earthquake, epicenters were situated within a small region with a dimension of about 5 km, and the focal depth increased. It shows that the rupture mainly extended from shallow part to deep in the vertical direction. The second phase was between theM _S=5.4 earthquake and theM _S=5.1 earthquake, earthquakes migrated along southeast, the focal depth decreased. It indicates that the rupture extended along southeast and from deep to shallow part. Foundation item: The Project of “Mechanism and Prediction of the Strong Continental Earthquake” (95-13-05-04). Contribution No. 01FE2017, Institute of Geophysics, China Seismological Bureau.     

2000年9～11月全球M≥5.0地震动态

根据中国地震局地球物理研究所中国数字地震台网数据管理中心 (CDSN DMC)从美国地震学合作研究会数据管理中心 (IRIS DMC)得到的资料 ,2 0 0 0年 9月全球范围内共发生 M≥ 5 .0地震 81次 (见表 1 ) ,发生在厄瓜多尔沿海的 M6 .6地震为 9月的最大地震。 9月发生的 81次 M≥5 .0地震中有 49次发生在东半球 ,32次发生在西半球。1 0月全球范围内共发生 M≥ 5 .0地震 1 1 9次 (见表 2 ) ,其中 7级以上地震 1次 ,即 1 0月 6日日本本州南部 7.0级地震。在 1 0月发生的 1 1 9次 M≥ 5 .0地震中有 76次发生在东半球 ,43次发生在西半球。东半…     

Ocean Ridge Granite and Its Geochemical Characteristics in Western Qinghai—Xizang Plateau

In our work,ocean ridge granite,i.e., Oytan plagiogranite massif,was discovered in western Qinghai-Xizang plateau.It intruded into the basic lava of the Oytag ophiolite suite and it was formed a little later than the (ultra)mafic rocks of the Oytag ophiolite suite.The Oytang plagiogranite possesses the geochemical characteristics of mantle-source granite and was formed in the “supre-subduction zone”(SSZ)ocean ridge environment,like the ocean ridge granite of Troodos,Cypus.     

Petrographic and geochemical evidence for the formation of primary, bacterially induced lacustrine dolomite: La Roda 'white earth' (Pliocene, central Spain)

Upper Pliocene dolomites (‘white earth’) from La Roda, Spain, offer a good opportunity to evaluate the process of dolomite formation in lakes. The relatively young nature of the deposits could allow a link between dolomites precipitated in modern lake systems and those present in older lacustrine formations. The La Roda Mg‐carbonates (dolomite unit) occur as a 3·5‐ to 4‐m‐thick package of poorly indurated, white, massive dolomite beds with interbedded thin deposits of porous carbonate displaying root and desiccation traces as well as local lenticular gypsum moulds. The massive dolomite beds consist mainly of loosely packed 1‐ to 2‐μm‐sized aggregates of dolomite crystals exhibiting poorly developed faces, which usually results in a subrounded morphology of the crystals. Minute rhombs of dolomite are sparse within the aggregates. Both knobbly textures and clumps of spherical bodies covering the crystal surfaces indicate that bacteria were involved in the formation of the dolomites. In addition, aggregates of euhedral dolomite crystals are usually present in some more clayey (sepiolite) interbeds. The thin porous carbonate (mostly dolomite) beds exhibit both euhedral and subrounded, bacterially induced dolomite crystals. The carbonate is mainly Ca‐dolomite (51–54 mol% CaCO₃), showing a low degree of ordering (degree of ordering ranges from 0·27 to 0·48). Calcite is present as a subordinate mineral in some samples. Sr, Mn and Fe contents show very low correlation coefficients with Mg/Ca ratios, whereas SiO₂ and K contents are highly correlated. δ¹⁸O‐ and δ¹³C‐values in dolomites range from ?3·07‰ to 5·40‰ PDB (mean=0·06, σ=1·75) and from ?6·34‰ to ?0·39‰ PDB (mean=?3·55, σ=1·33) respectively. Samples containing significant amounts of both dolomite and calcite do not in general show significant enrichment or depletion in ¹⁸O and ¹³C between the two minerals. The correlation coefficient between δ¹⁸O and δ¹³C for dolomite is extremely low and negative (r=?0·05), whereas it is higher and positive (r=0·47) for calcite. The lacustrine dolomite deposit from La Roda is interpreted mainly as a result of primary precipitation of dolomite in a shallow, hydrologically closed perennial lake. The lake was supplied by highly saturated HCO₃^?/CO₃^2? groundwater that leached dolomitic Mesozoic formations. Precipitation of dolomite from alkaline lake waters took place under a semi‐arid to arid climate. However, according to our isotopic data, strong evaporative conditions were not required for the formation of the La Roda dolomite. A significant contribution by bacteria to the formation of the dolomites is assumed in view of both petrographic and geochemical evidence.     

Skarns and Genesis of the Huanggang Fe-Sn Deposit, Inner Mongolia, China

Abstract: The skarns and genesis were studied of the Huanggang Fe‐Sn deposit and the nearby Sumugou Zn‐Pb deposit in Inner Mongolia, China. In the Huanggang mine, Nos. 1 to 4 Fe ore bodies are arranged along a calcareous horizon from proximal to distal in this order to a granite intrusion named Luotuochangliang, while Sn ore body is situated near another granite intrusion named 204. According to the distance from the granitic intrusions, mineral assemblages in skarns are systematically changed. Garnet is the most predominant skarn mineral throughout the deposit. Hastingsitic amphiboles, however, predominate in the proximal skarns. Fluorite is common in the proximal skarns, while instead calcite is common in the distal skarns. Chlorite is characteristically present only in No. 3 ore body, and chlorite geothermometry gives near 300C for the mineralization of later stage. When garnet crystal shows zonal structure, isotropic andraditic garnet occupies the core, and is surrounded with anisotropic less‐andraditic garnet. The presence of white skarn along the boundary between main skarns and host sedimentary rocks confirms relatively reducing environment prevailing as a whole in the studied area. However, the compositional relation between coexisting garnet and clinopyroxene demonstrates that relatively oxidizing condition was achieved for garnet skarn and magnetite ore in the distal, Nos. 2 to 4 Fe ore bodies and Sumugou deposit, compared to that for garnet skarn in the proximal, No. 1 and Sn ore bodies. Preliminary study on the tin content of garnets in the studied area revealed a certain degree of contribution brought from granitic intrusives since the early stage of skarn formation, irrespective of proximal or distal. Oxygen isotope study on garnet, magnetite, quartz and skarn calcite, as well as hydrogen isotope study on hastingsitic amphibole, demonstrates mainly meteoric water origin for the skarn– and ore‐forming solutions. The occurrence of Sn, W, Mo and F minerals indicates that those elements were mainly supplied to the deposit later than the formation of skarns and iron ores, overlapping to them. These constraints allow to delineate the formation model of the deposit as follows (Fig. 10): At the time of late Jurassic to early Cretaceous, felsic activity occurred in this region as a part of Yanshanian magmatism, and formed granitic intrusions as well as thick volcanic piles on the surface. The circulation of meteoric water was provoked by the heat brought by the intrusions. By this circulation, much amount of iron was extracted from andesites of the Dashizhai Formation, and precipitated as skarns and magnetite ores along calcareous horizons near the bottom of the Huanggangliang Formation. Subsequently, volatile‐rich fluids with Sn, W and Mo were expelled from the solidifying granitic magmas, and precipitated these metals in the pre‐existing skarns and ores.     

金刚石碎岩工具胎体材料添加稀土元素的试验研究

对胎体材料中添加稀土元素问题进行了试验研究。对添加稀土和未加稀土的胎体性能进行测试，结果表明，添加稀土比未加稀土的胎体材料的抗弯强度、硬度和冲击韧性均有所提高，其中抗弯强度提高了10％－62％，冲击韧性提高了5％。胎体中添加稀土对提高胎体和金刚石碎岩工具的技术经济指标具有重要作用,并且为在胎体材料中实现以Fe代Co创造了有利条件。     

大气臭氧与气溶胶垂直分布的高空气球探测

本文给出了1993年9月12日利用高空科学气球在河北省香河地区探测到的大气臭氧和气溶胶的垂直分布。结果发现:(1) 大气臭氧的数密度在整个对流层较低(～10[12]mol/cm3)，并从地面到对流层顶略有下降；对流层顶以上开始快速增加，极值层高度在～24 km，其值为4.78×10[12]mol/cm3；臭氧分压有类似的分布特征，极值146×10[-4]Pa，位于同一高度；(2) 在平流层低层，臭氧分压有一个次极值62×10[-4]Pa，位于15～16 km；(3) 0～30 km大气气溶胶数密度呈现出三个峰值:143，8和1.1 个/cm[3]，分别位于近地面、5 km和21 km；（4）气溶胶的数密度谱在对流层为双模态；在平流层，次峰消失。同时，我们还与其他观测结果作了比较分析。     

近海地震活动特征及其测震学前兆的某些研究

利用反映震级－频度关系的参量Ｃ值，η值，ｂ值和ｂ值谱以及反映地震空间分布的森下指等研究了近海地震活动的一些主要特征，发现近海强震前地震活动性指标及图象的变化特征与陆地上强震前的特征存在一定差异；给出了新研究的可用于近海及滨海地区强震预报的短期和临震     

华北地区地震立交成因研究及山西地震带强震预测

利用立交模式的原理，对华北地区历史地震进行了回顾性检验，并对山西地震带具有立交成因的强震危险地区进行了预测。结果表明太原盆地南端、大同盆地南端和北端、忻定盆地中段是可能孕育大震的地区。     

北京地区震磁观测研究

旨地探索研究地震预报而开展的北京地区地磁观测，在震磁前兆研究与地震预测试验方面都获得了可喜的进展，本文分析了１９９０－１９９５年北京及其西部地区的地磁观测资料，研究了地磁异常信息，预测了地震活动趋势，提出了今后应加强监测与研究的区域。