Explosion seismic P and S velocity and attenuation constraints on the lower crust of the North–Central Tibetan Plateau, and comparison with the Tethyan Himalayas: Implications on composition, mineralogy, temperature, and tectonic evolution

P and S velocity and attenuation estimates in the lower crust are obtained from a set of wide angle reflection–refraction profiles in the region of active tectonics at the NE edge of the Tibetan Plateau and discussed together with respect to similar data at its Himalaya–south Tibet edge.The quality factor is estimated in the lower half of the crust by accounting for the differential effect on amplitude–frequency observed between waves of different penetrations, and both in P and S modes. Attenuation values allow to exclude a significant proportion of partial melt and to estimate the homologous temperature, ratio of in situ to solidus absolute temperatures. The latter depend on the physical conditions being of dry, wet or dehydration melting, which are found different among the regions of the northern Bayan Har and northern Qang Tang boundaries between blocks, as well as the Tethyan–Himalayas, south of the Indus–Tsangpo suture. Their in situ temperatures differ also as estimated from their different V_p for a similar felsic composition.Joint measurement of several parameters, V_p, V_s, Q_p and Q_s reveals the composition, mineralogy, temperature and hydration conditions of the lower half of the thickened crust of Tibet that may be discussed in terms of evolution. The material presently in the thickened crust, even its lower part, has a felsic composition, upper to middle crustal lithology, and the temperature conditions estimated suggest that basic material that could have underlain it could be eclogitized and not appear anymore above the seismic Moho.Under northern Qang Tang, the felsic material in the lower half of the crust appears as hot and dry. Its burial may have occurred earlier or may have been moderate in the postcollisional phase. This is consistent with a model of indentation of the Qang Tang crust by an originally thinner Bayan Har crust to bring part of its crust to greater depth, suggested from imaging the crustal architecture. Under northern Bayan Har, the material in the lower half of the crust appears as felsic, at low temperature and not dry conditions. This is evidence that it has been transported from a shallower depth, and this recently enough not to be yet dehydrated and temperature equilibrated in a conductive geotherm. It supports a model of recent overriding of the middle crust of the north Kun Lun block to the north independently suggested from the image of crustal architecture. The Tethyan Himalayas case appears bracketed by these two cases in northern Tibet for V_p and temperature conditions, but shows highest attenuation in the lower crust that is colder but less dry than under northern Qang Tang.     

化爆标定地震定位方法研究

定位仿真表明,若标定震源在网内,震中偏差和震源深度偏差等值线都是以标定震源为圆心的同心圆,网内大约30%的事件,震中偏差为5%;如果标定震源位于台网一侧,约10%事件的震中误差为10%。无论标定源在网内还是在网外,计算震中都向标定震源方向移动,距标定点愈远,定位偏差愈大。速度标定定位显示,规则地震台网中对称线上的震源定位是不可靠的。实际网内化爆标定定位表明,对于网内事件,爆炸邻域定位精度比速度标定定位精度高;对于网外事件,邻域标定定位精度比速度标定定位精度低。     

环肋圆柱壳体在水下冲击波作用下的动力弹塑性屈曲

本文以加肋圆柱壳体为对象建立力学模型，在水下爆炸产生的冲击波作用下，考虑流体与结构的耦合效应，研究加肋圆柱壳体的弹塑性失稳变形量及动力响应特性。数值分析显示出的最终变形形状和压力变化过程与实验资料一致的     

康山“古油藏”讨论之三——康山“沥青脉”的成因

通过对康山固体可燃脉体产状、脉石矿物性质、构造发展史的综合分析,认为其成因很可能是下寒武统荷塘组中的软沥青和有机质,在加里东运动期间,由于区域应力体系的变化而爆炸运移形成的。康山脉石矿物是沥青和有机质,不是煤和无机物。沥青的源岩为下寒武统荷塘组富有机质的黑色泥岩、硅质泥岩、硅质岩。康山脉中的固体沥青和有机质,当初挤入时应呈塑性流动状态,康山沥青系由石油经热演化而成。     

利用人工爆破资料研究福建一维P波速度结构和地震定位

通过人工爆破资料研究地球结构的独特优点是震源时间和位置精确知道.2010-2012年间福建省进行了一系列的爆破实验.本文利用手工拾取来自省地震台网记录的爆破地震初至Pg、Pn以及续至Pg波到时数据,采用联合反演方法构建了新的一维P波速度模型,即福建爆破模型（FJEM）.与华南模型相比,FJEM模型对走时的拟合程度提高了45%,有明显改善.利用不同爆破地震数据组合得到稳定类似的福建地区一维速度模型,显示福建地区存在较简单的一维速度结构.对爆破地震的重定位显示传统使用的华南模型在福建地区具有较小的水平定位误差（平均0.52±0.45 km）,但存在较大深度误差（平均4.7±1.2 km）.FJEM模型表现出与华南模型相似的水平定位能力,但是震源深度误差更小（1.3±1.1 km）.对基于FJEM模型的合成天然地震目录的重定位,华南模型显示出相似的定位结果：（1）台站方位覆盖较好的福建中部地区的水平定位误差小;（2）台站方位覆盖差的福建海岸及海峡区域水平定位误差大;（3）震源深度误差则跟台站数目及方位分布没有明显的关系,而是与发震时间误差有互易关系.从中可以看出,地震水平定位误差基本上受台站方位覆盖影响,而受参考速度模型影响不大;而在深度方面,本文改进的FJEM模型不仅更加接近真实的速度结构（拟合走时更好）而且也减小了深度误差.因此建议在福建及其邻近区域的日常定位中用FJEM模型替代华南模型.

     

Modelling rock fracturing and blast-induced rock mass failure via advanced discretisation within the discontinuous deformation analysis framework

Rock mass failure is a particularly complex process that involves the opening and sliding of existing discontinuities and the fracturing of the intact rock. This paper adopts an advanced discretisation approach to simulate rock failure problems within the discontinuous deformation analysis (DDA) framework. The accuracy of this approach in continuum analysis is verified first. Then, the advanced discretisation approach for fracturing modelling is presented, and the discretisation strategy is discussed. Sample rock static failures are simulated and the results are compared with experimental results. Thereafter, with a generalised definition of the artificial joints, this approach is further extended and applied in the simulation of blast-induced rock mass failures in which the instant explosion gas pressure obtained by the detonation pressure equation of state is loaded on the main blast chamber walls and the induced surrounding connected fracture surfaces. In the simulation instance of rock mass cast blasting, the whole process, including the blast chamber expansion, explosion gas penetration, rock mass failure and cast, and the formation of the final blasting pile, is wholly reproduced.     

建筑物下爆破地震效应的研究——"爆破安全规程"的应用与修正

叙述了大姚铜矿的大药量爆破振动效应观测,研究了在建筑物下的爆破施工中,如何确保建筑物安保证安全生产最大用药量的问题,结合“爆破安全规程”药量指数m的应用与修正,从而得出正在对爆破上方的建筑物地面爆破振动动加速度a,速度v随爆心距地面投影r与爆心深度h之比值（r/h)的衰减变化规律;发现临近正对爆心的地面振动有强心现象,并定义它为“极震”效应;定义“极震”效应系数N为正对爆心实测加速度a或速度v与用振动衰减普适式求得值a'或v'之比（N＝a/a',或N=v/v'）。经多年的安全生产证明,采用振动衰减普适式（药量指娄m=1/3)和“极震”效应系数修正法,效果良好,获得生产最佳用药量,民房安全率达98％左右。     

Carbon isotope chemostratigraphy of a Precambrian/Cambrian boundary section in the Three Gorge area, South China: Prominent global-scale isotope excursions just before the Cambrian Explosion

Carbon isotope chemostratigraphy has been used for worldwide correlation of Precambrian/Cambrian (Pc/C) boundary sections, and has elucidated significant change of the carbon cycle during the rapid diversification of skeletal metazoa (i.e. the Cambrian Explosion). Nevertheless, the standard δ¹³C curve of the Early Cambrian has been poorly established mainly due to the lack of a continuous stratigraphic record. Here we report high-resolution δ¹³C chemostratigraphy of a drill core sample across the Pc/C boundary in the Three Gorge area, South China. This section extends from an uppermost Ediacaran dolostone (Dengying Fm.), through a lowermost Early Cambrian muddy limestone (Yanjiahe Fm.) to a middle Early Cambrian calcareous black shale (Shuijingtuo Fm.). As a result, we have identified two positive and two negative isotope excursions within this interval. Near the Pc/C boundary, the δ¹³C_carb increases moderately from 0 to + 2‰ (positive excursion 1: P1), and then drops dramatically down to − 7‰ (negative excursion 1: N1). Subsequently, the δ¹³C_carb increases continuously up to about + 5‰ at the upper part of the Nemakit–Daldynian stage. After this positive excursion, δ¹³C_carb sharply decreases down to about − 9‰ (N2) just below the basal Tommotian unconformity. These continuous patterns of the δ¹³C shift are irrespective of lithotype, suggesting a primary origin of the record. Moreover, the obtained δ¹³C profile, except for the sharp excursion N2, is comparable to records of other sections within and outside of the Yangtze Platform. Hence, we conclude that the general feature of our δ¹³C profile best represents the global change in seawater chemistry. The minimum δ¹³C of the N1 (− 7‰) is slightly lower than carbon input from the mantle, thus implying an enhanced flux of ¹³C-depleted carbon just across the Pc/C boundary. Hence, the ocean at that time probably became anoxic, which may have affected the survival of sessile or benthic Ediacaran biota. The subsequent δ¹³C rise up to + 5‰ (P2) indicates an increase of primary productivity or an enhanced rate of organic carbon burial, which should have resulted in lowering pCO₂ and following global cooling. This scenario accounts for the cause of the global-scale sea-level fall at the base of the Tommotian stage. The subsequent, very short-term, and exceptionally low δ¹³C (− 9‰) in N2 could have been associated with the release of methane from gas hydrates due to the sea-level fall. The inferred dramatic environmental changes (i.e., ocean anoxia, increasing productivity, global cooling and subsequent sea-level fall with methane release) appear to coincide with or occur just before the Cambrian Explosion. This may indicate synchronism between the environmental changes and rapid diversification of skeletal metazoa.     

New Localities and Palaeoscolecid Worms from the Cambrian (Stage 4, Series 2) Guanshan Biota in Kunming, Yunnan, South China

The Guanshan Biota from the Cambrian Stage 4 Wulongqing Formation is a typical Burgess-shale type Lagerst?tte that had witnessed the Cambrian explosion. Here we report two new localities of the Guanshan Biota, which is located at Baimei village, south of Kunming and Xinglong village, Wuding County, Yunnan Province respectively. Both localities produce soft-body fossils and several new taxa, e.g. a new species of palaeoscolecidans (Palaeoscolex xinglongensis sp. nov.) reported herein. The comparative study of the new species with similar form not only indicates that there is a diversification of palaeoscolecid species in Guanshan Biota, but also strengthens the ties between the older Chengjiang Biota and the younger Kaili Biota (and also the coeval Burgess Shale community). Three paleoecological features, including high diversity, little disparity and richness of palaeoscolecid worms, are summarized as a case study to represent the differences between Guanshan and Chengjiang Biota.     

Coupes sismiques des structures superficielles dans les petites antilles—I: Guadeloupe

Summary In 1976 and 1977, seismic profiles were carried out in Guadeloupe. Two profiles were established in the area of La Soufriére volcano and one profile through the northern part of Guadeloupe and southern part of Grande Terre. The two first profiles were occupied from 1 to 30 km and the third profile between 5 and 50 km.The interpretation shows that the superficial structures are characterized by a three-layers model: the compressional velocity is about 2.7 to 3.0 km/s down to a depth from 1 to 3 km. Below this, the velocity is between 4.0 and 4.5 km/s in a layer whose thickness varies from 1 to 2.5 km. Under this layer we find a 6.0–6.1 km/s layer which is one of the two known crustal layer under Lesser Antilles. The boundary between the old and new are which form the Lesser Antilles arc, is marked by a thicker layer of sediments on the eastern flank of recent volcanic chain.