Shear wave anisotropy in D＂ region beneath the western Pacific

Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC and IRIS, and from 26 northeast Asia and north Pacific events recorded by IRIS, we studied the shear wave anisotropy in D" region beneath the western Pacific utilizing the ScS-S differential travel time method and obtained the splitting time values between the radial and transverse components of each ScS wave corresponding to each core-mantle boundary (CMB) reflection point. We found that most shear waves involved horizontally polarized shear wave components traveling faster than vertically polarized shear wave components through the D" region. The splitting time values of ScS wave range from ?0.91 s to 3.21 s with an average value of 1.1 s. The strength of anisotropy varies from ?0.45% to 1.56% with an average value of 0.52%. The observations and analyses show that in the D" region beneath the western Pacific the lateral flow is expected to be dominant and the vertical transverse isotropy may be the main anisotropic structure. This structure feature may be explained by the shape preferred orientation of the CMB chemical reaction products or partial melt and the lattice preferred orientation of the lower mantle materials caused by the lateral flow at lowermost mantle.     

Seismic microzonation of Dehradun City using geophysical and geotechnical characteristics in the upper 30 m of soil column

The understanding of geotechnical characteristics of near-surface material is of fundamental interest in seismic microzonation. Shear wave velocity (Vs), one of the most important soil properties for soil response modeling, has been evaluated through seismic profiling using the multichannel analysis of surface waves in the city of Dehradun situated along the foothills of northwest Himalaya. Fifty sites in the city have been investigated with survey lines between 72 and 96 m in length. Multiple 1-D and interpolated 2-D profiles have been generated up to a depth of 30–40 m. The Vs were used in the SHAKE2000 software in combination with seismic input motion of the recent Chamoli earthquake to obtain site response and amplification spectra. The estimated Vs are higher in the northern part of the study area (i.e., 200–700 m/s from the surface to a depth of about 30 m) as compared to the south and southwestern parts of the city (i.e., 180–400 m/s for the same depth range). The response spectra suggest that spectral acceleration values for two-story structures are three to eight times higher than peak ground acceleration at bedrock. The analysis also suggests peak amplification at 3–4, 2–2.5, and 1–1.5 Hz in the northern, central, and south-southwestern parts of the city, respectively. The spatial distributions of Vs and spectral accelerations provide valuable information for the seismic microzonation in different parts of the urban area of Dehradun.     

Wintertime Seasonal Scale Simulation over Western Himalaya Using RegCM3

The Himalayan region of north India is composed of complex mountain ranges with different altitudes and orientations, causing prevailing weather conditions to be complex. Wintertime eastward moving synoptic weather systems `Western Disturbances' (WDs) yield large amounts of precipitation over this region. Numerous micro/mesoscale circulations become generated along with prevailing weather due to surface heterogeneity and land-use variability of the Himalayan region. WDs along with these circulations may give rise to very adverse weather conditions over the region. Intraseasonal variability of surface climate over the Himalayas is studied using regional climate model (RegCM3) with 60 km resolution. A 6-month (Oct. 1999–Mar. 2000) period, as this period has received an enormous amount of precipitation in the form of snow, is considered to study surface climate variability in terms of temperature, precipitation and snow amount. Model simulations show cold bias over the Himalayan region and warm bias over the northwest India. Average monthly distribution of temperature indicates that a controlled experiment could capture the areas of lowest temperature regime. Precipitation fields could be simulated only up to a certain degree of satisfaction and the influence of topographic elevation and valleys needs to be seen. RegCM3 provides a representation of resolvable atmospheric circulations that results in explaining mean variability during winter.     

Nonlinear Analysis of the Frequency-magnitude Relationship in the Western Circum-Pacific Region

— It has long been realized that the linear Gutenberg-Richter model arduously describes the frequency-magnitude relationship for the magnitude span ranging from small to large earthquakes because of the breakdown of the self-similarity rule due to the changing scaling of the magnitude. Three different segments should be observed from small (usually M < 3.0), through moderate (M < M_c, where M_c is the frequency-magnitude turning point caused by the seismogenic thickness), to large earthquakes (M M_c). We will only concentrate on the moderate and large earthquakes due to their importance. The breakdown of the self-similarity rule from moderate to large earthquakes occurs where the earthquake is big enough to cut through the entire seismogenic layer. A nonlinear hyperbolic model, which fits two linear relations smoothly, is studied in the present paper, where N is the cumulative number of earthquakes with magnitudes larger than or equal to M; a₁ to a₅ are constants to be calculated. The G-R linear relation is actually a special case of the present nonlinear model, i.e., a₃ or a₅ equal to zero. The nonlinear form, with the support of a reasonable physical mechanism, can generally give a better fitting with comparatively minor errors for complete data sets, especially for the areas where large earthquakes are numerous. In order to demonstrate its superiority to the linear G-R relation, thirteen seismogenic zones are examined around the western part of the Circum-Pacific region and western part of China and it is found that the fitting errors from this nonlinear model are, as expected, generally much smaller than those for G-R. Furthermore, the parameter a₄ is believed to relate with the saturated magnitude M_c,which to some extent reflects the mean thickness of the seismogenic layer.Acknowledgement. The author thanks Dr Paul W. Burton for his useful discussions. He appreciates two anonymous reviewers comments and suggestions which enhanced the quality of the paper. This research was partially supported by the project EPAN-M.4.3/2013555 of bilateral cooperation between Greece and China funded by the General Secretariat of Research & Technology of Greece and by the project of UK-China Science and Technology Fund funded by the British Council. Some figures were made with GMT software (WESSEL and SMITH, 1995).     

The regional development in a multi-cultural background

China is a country with many nationalities. Each of them has formed its own special culture, which is different from the mainstream of majority Han nationality, by adapting to geo-environment during history. Due to different backgrounds, the regional developmental model of minorities in the western China is different from the Han nationality and western countries. Combining a knowledge-based civilization and sustainable development, the minority areas can seek the systematic integration of culture-economy-ecology. Based on this, the paper suggests that the minority areas in western China should take the way of emphasizing developmental quality rather than developmental quantity for a harmonious system of culture-economy-ecology. Some approaches for developing minority areas in western China have been put foreword. Foundation item: Under the auspices of the National Natural Science Foundation of China (No. 49261001). Biography: LU La-chang (1963 —), male, a native of Shaanxi Province, Ph. D., professor. His research interests include urban and regional studies. E-mail: lachanglu@163.net     

兰坪—思茅盆地砂页岩中脉状铜矿床的特征及成因

兰坪－思茅中新生代盆地中的铜矿床,主要产于由砂岩、粉砂岩和页岩组成的含盐结色碎屑岩建造中,故一些研究者将其与典型的陆相砂页型铜矿床相类比。但就铜矿化的产出形式、元素的矿物组合、矿石稀土配分特征以及同位素组成特点等而言,均与典型砂页岩型铜矿床存在显著差异,而与一些地热区的矿化作用相似。说明研究区砂矾岩中的铜矿床具有特殊的成矿机理。     

川西义敦岛弧带晚三叠世植物化石

通过 1∶2 5万区域地质调查和三叠系专项研究 ,在义敦岛弧带的四川省新龙县雄龙西、白玉县热加获得一批植物化石 ,计 15属 2 0种 ,其中包括两个新种 ,一个属种为国内首次发现。这些化石不仅丰富了本区植物化石组合内容 ,而且对地层时代的确定及与邻区的对比和沉积环境的恢复提供了重要的古生物依据。     

西部开发的资源战略问题

西部的资源赋存并不丰富。对全国经济发展有巨大意义的关键性资源并不多 ,由资源特性和经济发展的趋势决定了东部地区对西部地区资源的依赖降低 ,对于西部长期以资源开发为重点的发展模式所造成的多种疾患 ,以及目前国内外资源环境形势 ,提出西部注重开发技术、知识资源 ,培育特色产业 ,大力发展旅游业和建立国家资源安全战略的西部开发资源战略     

新疆西天山那拉提构造带变质核部杂岩地质构造特征

新疆西天山那拉提构造带变质核部杂岩分布于新疆巩留县那拉提山山脊北侧，整体沿那位提南缘构造带北侧呈近东西向展布，为一套由高级变质表壳岩、灰色片麻岩组成的早前寒武系高级片麻岩系，历经多期不同构造体制变形变质改造与再造，形成多相片麻岩系，并呈长垣状变质核部杂岩隆升，构成那拉提造山带的核部构造物质组成。     

祁连山西段古元古代北大河岩群中斜长角闪岩的地球化学特征及构造背景

以大陆碎块形式残存于北祁连造山带内部的古元古代北大河岩群早期发育有大量的斜长角闪岩,其原岩为玄武岩,Alk-∑FeO-MgO图解、REE特征、里特曼组合指数等均显示斜长角闪岩属钙碱性系列范围,个别显示弱碱性,斜长角闪岩具有较高的Al2O3、∑FeO和低的Mg#,这些特点反映其成分演化程度较高,表明火山岩的形成与古老地壳的活化有关,有较强分异的稀土元素分配模式,在Ti-Zr-Y图、Ni-FeO/MgO图解和Ta/Yb-Th/Yb图解上斜长角闪岩均显示火山弧或活动大陆边缘的特点,在玄武岩的地球化学形式图、稀土元素整体特征与钙碱性岛弧玄武岩基本相同;87Sr/86Sr=0.71617～0.72033,143Nd/144Nd=0.512414～0.512495,εNd=-2.79～-4.37.显示出壳源性质或者是受到大陆下地壳的混染作用而形成.因此推测斜长角闪岩的原岩为不同程度部分熔融的岩浆弧作用的产物,说明在古元古代华北克拉通和柴达木克拉通之间存在古洋盆的俯冲消减.