Velocity structure of the crust and uppermost mantle in the boundary area of the Tianshan Mountains and the Tarim Basin

A portable 3-component broadband digital seismic array was deployed across the Tianshan orogenic belt (TOB) to investigate the lithospheric structure. Based on receiver function analysis of the teleseismic P-wave data, a 2-D S-wave velocity profile of the boundary area of the TOB and the Tarim Basin was obtained at the depths of 0--80 km.Our results reveal a vertical and lateral inhomogeneity in the crust and uppermost mantle. Four velocity interfaces divide the crystalline crust into the upper, middle and lower crust. A low velocity zone is widely observed in the upper-middle crust. The depth of Moho varies between 42 and 52 km. At the north end of the profile the Moho dips northward with a vertical offset of 4--6 km, which implies a subduction front of the Tarim Basin into the TOB. The Moho generally appears as a velocity transitional zone except beneath two stations in the northern Tarim Basin, where the Moho is characterized by a typical velocity discontinuity. The fine velocity structure and the deep contact deformation of the crust and upper most mantle delineate the north-south lithospheric shortening and thickening in the boundary area of the TOB and the Tarim Basin, which would be helpful to constructing the geodynamical model of the intracontinental mountain-basin-coupling system.     

Fine three-dimensional P-wave velocity structure beneath the capital region and deep environment for the nucleation of strong earthquakes

A detailed 3-D P-wave velocity model of the crust and uppermost mantle under the capitol region is determined with a spatial resolution of 25 km in the horizontal direction and 4-17 km in depth. We used 48750 precise P-wave arrival time data from 2973 events of local crustal earthquakes, controlled seismic explosions and quarry blasts. These events were recorded by 123 seismic stations. The data are analyzed by using a 3-D seismic tomography method. Our tomographic model provides new information on the geological structure and complex seismotectonics of this region. Different patterns of velocity structures show up in the North China Basin, the Taihangshan and the Yanshan Mountainous areas. The velocity images of the upper crust reflect well the surface geological, topographic and lithological features. In the North China Basin, the depression and uplift areas are imaged as slow and fast velocity belts, respectively, which are oriented in NE-SW direction. The trend of velocity anomalies is the same as that of major structure and tectonics. Paleozoic strata and Pre-Cambrian basement rocks outcrop widely in the Taihangshan and Yanshan uplift areas, which exhibit strong and broad high-velocity anomalies in our tomographic images, while the Quaternary intermountain basins show up as small low-velocity anomalies. Most of large earthquakes, such as the 1976 Tangshan earthquake (M 7.8) and the 1679 Sanhe earthquake (M 8.0), generally occurred in high-velocity areas in the upper to middle crust. However, in the lower crust to the uppermost mantle under the source zones of the large earthquakes, low-velocity and high-conductivity anomalies exist, which are considered to be associated with fluids, just like the 1995 Kobe earthquake (M 7.2) and the 2001 Indian Bhuj earthquake (M 7.8). The fluids in the lower crust may cause the weakening of the seismogenic layer in the upper and middle crust and thus contribute to the initiation of the large crustal earthquakes.     

Evidence of crustal ＇channel flow＇ in the eastern margin of Tibetan Plateau from MT measurements

Magnetotelluric （MT） survey has been carried out in the eastern margin of the Tibetan Plateau and its neighboring Shimian-Leshan area, Sichuan Province. Analysis of this MT data reveals that the electric structure of the Tibetan Plateau differ much from that of the Sichuan block. In general, the electric resistivity of crust beneath the Sichuan block in the east is larger than that of the eastern margin of the Tibetan Plateau in the west. The crust of the plateau is divided into upper, middle, and lower layers. The middle crust is a low resistivity layer with minimum down to 3-10Ωm about 10-15 km thick. It presumably contains partial melt and/or salt-bearing fluids with low viscosity, prone to deform and flow, producing a ＂channel flow＂ under the southeastward squeeze of the eastern Tibetan Plateau. This low-resistivity layer makes the upper crust decoupled mechanically from the lower crust. In the brittle upper crust, faults are dominated by left-lateral strike-slip and thrust motions, leading to surface rising and shallow earthquakes. The low-resistivity layer also cut the Xianshuihe-Anninghe fault zone into two sections vertically. In this region, the thicknesses of upper, middle, and lower crust vary laterally, producing a transitional zone in the eastern margin of the Tibetan Plateau characterized by thicker crust and higher elevation in the west and thinner crust and lower elevation in the east.     

The distribution of the oil derived from Cambrian source rocks in Lunnan area,the Tarim Basin,China

There are great differences in biomarks between Cambrian oil and Middle-Upper Ordovician oil. In this stuty, the authors analyzed 40 oils found in Lunnan area by GC-MS and calculated the content of Cambrian oil in the 40 oils according to the steroid indexes of typical oil mixture and match experiment. The results show that it is a general phenomenon in Ordovician reservoir that the oil derived from Cambrian source rock mixed with the oil derived from Middle-Upper Ordovician source rock in Lunnan area, the mixture degree of the two oils is lower in Carboniferous reservoir than in Ordovician reservoir, and the oils kept in Triassic reservoir have single source, Middle-Upper Ordovician source rock. The mixture oils mainly composed of Cambrian oil (>50%) distributed in Sangtamu fault zone, and the oils found in Lunnan fault zone are Middle-Upper Ordovician oil. This distribution of oils in Lunnan area is owing to that Lunnan fault zone is located in anticline axis part, Lunnan fault zone underwent serious erosion, and the oils from Cambrian source rock accumulated in Lunnan fault zone were degraded completely during Caledonian-Hercynian movement. But the Cambrian oil accumulated in Sangtamu fault zone was not degraded completely and some of them were left for the location of Sangtamu fault zone is lower than Lunnan fault zone. Later, the oil derived from Middle-Upper Ordovician source rock mixed with the remained Cambrian oil, and the mixture oil formed in Sangtamu fault zone.     

The distribution of the oil derived from Cambrian source rocks in Lunnan area, the Tarim Basin, China

There are great differences in biomarks between Cambrian oil and Middle-Upper Ordovician oil. In this stuty, the authors analyzed 40 oils found in Lunnan area by GC-MS and calculated the content of Cambrian oil in the 40 oils according to the steroid indexes of typical oil mixture and match experiment. The results show that it is a general phenomenon in Ordovician reservoir that the oil derived from Cambrian source rock mixed with the oil derived from Middle-Upper Ordovician source rock in Lunnan area, the mixture degree of the two oils is lower in Carboniferous reservoir than in Ordovician reservoir, and the oils kept in Triassic reservoir have single source, Middle-Upper Ordoviclan source rock. The mixture oils mainly composed of Cambrian oil （〉50%） distributed in Sangtamu fault zone, and the oils found in Lunnan fault zone are Middle-Upper Ordovician oil. This distribution of oils in Lunnan area is owing to that Lunnan fault zone is located in anticline axis part, Lunnan fault zone underwent serious erosion, and the oils from Cambrian source rock accumulated in Lunnan fault zone were degraded completely during Caledonian-Hercynian movement. But the Cambrian oil accumulated in Sangtamu fault zone was not degraded completely and some of them were left for the location of Sangtamu fault zone is lower than Lunnan fault zone. Later, the oil derived from Middle-Upper Ordovician source rock mixed with the remained Cambrian oil, and the mixture oil formed in Sangtamu fault zone.     

Synthetic seismograms of ground motion near earthquake fault using simulated Green’s function method

Seismograms near source fault were synthesized using the hybrid empirical Green＇s function method where the discretely simulated seismic waveforms are used for Green＇s functions instead of the observed waveforms of small earthquakes. The Green＇s function seismic waveforms for small earthquake were calculated by solving wave equation using the pseudo-spectral method with the staggered grid real FFT strategy under a detailed 2-D velocity structure in Kobe region. Magnitude and seismic moment of simulated Green＇s function waveforms were firstly determined by using the relationship between fault length and corner frequency of source spectrum. The simulated Green＇s function waveforms were employed to synthesize seismograms of strong ground motion near the earthquake fault. The synthetic seismograms of the target earthquake were performed based on the model with multiple source rupture processes. The results suggest that synthesized seismograms coincide well with observed seismic waveforms of the 1995 Hyogo-ken Nanbu earthquake. The simulated Green＇s function method is very useful for prediction of the strong ground motion in region without observed seismic waveforms. The present technique spreads application field of the empirical Green＇s function method.     

Some thoughts on seismotectonics of major earthquake occurrence zones in China

A major earthquake occurrence zone means a place where M≥6 events have occurred since the Holocene and similar shocks may happen again in the future. The dynamic context of the major earthquake occurrence zones in China is primarily associated with the NNE-directed push of the India plate,next with the westward subduction of the Pacific plate. The Chinese mainland is a grand mosaic structure of many crust blocks bounded by faults and sutures. When it is suffered from boundary stresses,deformation takes place along these faults or sutures while the block interiors remain relatively stable or intact. Since the Quaternary,for example,left slip on the Xianshuihe-Xiaojiang fault zone in southwestern China has produced a number of fault-depression basins in extensional areas during periods Q1 and Q2. In the Q3,the change of stress orientation and enhancement of tectonic movement made faults of varied trends link each other,and continued to be active till present day,producing active fault zones in this region. Usually major earthquakes occur at some special locations on these active fault zones. During these events,in the epicenter areas experience intensive deformation characterized by large-amplitude rise and fall of neighboring sections,generation of horst-graben systems and dammed rivers. The studies on palaeoearthquakes suggest that major shocks of close magnitudes often repeated for several times at a same place. By comparison of the Chi-Chi,Taiwan event in 1999 and Yuza,Yunnan event in 1955,including contours of accelerations and intensities,destruction of buildings,and in contrast to the Xigeda formation in southwestern China,a sandwich model is established to account for the mechanism of deformation caused by major earthquakes. This model consists of three layers,i. e. the two walls of a fault and the ruptured zone intercalated between them. This ruptured zone is just the loci where stress is built up and released,and serves as a channel for seismic waves.     

Seismicity characteristics of the 2011 <Emphasis Type="Italic">M</Emphasis>9.0 Tohoku earthquake near the East Coast of Honshu in Japan

The spatiotemporal evolution of the M9.0 Tohoku earthquake sequence off the East Coast of Honshu in Japan on March 11,2011 and precursive seismic activity near the Japan Trench show that the earthquake sequence has foreshock-main shock-aftershock characteristics.Its foreshock sequence is characterized by a concentrated spatial distribution,low b value and the same focal mechanisms.Half an hour after the main shock,the two greatest aftershocks,with magnitudes of M7.9 and M7.7,occurred,followed by a rapid reduction in the strength of events.The aftershock activity was enhanced roughly two weeks and one month after the main event.This great earthquake ruptured bilaterally.Five hours after the main shock,the aftershock zone extended over a range that was 500 km in length and 300 km in width.A day later,the long axis of the aftershock area had expanded to about 600 km.Nine years prior to the 2011 earthquake,the seismicity in the location of the seismic source for this event enhanced significantly,with the extent of this area of enhanced seismicity being roughly equivalent to the aftershock zone.     

Interseismic and coseismic displacements of the Lushan Ms 7.0 earthquake inferred from leveling measurements

By using precise leveling data observed between 1985 and 2010 across the south section of the Longmenshan fault zone, and eliminating the coseismic displacements caused by the Wenchuan Ms 8.0 earthquake, the interseismic vertical deformation field was obtained. The result shows that the Lushan region, located between the Shuangshi-Dachuan fault （front range of the Long- menshan fault） and the Xinkaidian fault （south section of the Dayi fault）, is situated in the intersection zone of positive and negative vertical deformation gradient zones, indicating that this zone was locked within 25 years before the Lushan earthquake. Based on leveling data across the rupture zone surveyed between 2010 and 2013, and by eliminating the vertical deformation within 3 years before the earthquake, the coseismic vertical displacement was derived. The coseismic vertical displacement for the benchmark DD35, which is closest to the epicenter, is up to 198.4 mm （with respect to MY165A）. The coseismic dis- placement field revealed that the northwest region （hanging wall） moved upwards in comparison with the southeastern region （foot wall）, suggesting that the seismogenic fault mainly underwent thrust faulting. By comparing the coseismic and interseismic vertical deformation fields, it was found that the mechanisms of this earthquake are consistent with the elastic rebound theory; the elastic strain energy （displacement deficit） accumulated before the Lu- shan earthquake was released during this quake.     

Effect of the free surface on the earthquake energy: A case study of reverse faulting

Based on the representation theorem of seismic energy radiation, in this study, we have quantitatively investigated the effect of free surface on the radiation energy distribution due to a coupling interaction between free surface and near surface finite fault for the reverse earthquake faulting. Corresponding to the finite faulting, a 2-D pseudostatic-reverse-fault-dislocation solution has been used in the calculation of the work done by the seismic response against free surface. The results indicate that, due to a strong coupling interaction between the free surface and near surface fault, the total radiated seismic energy ER is much larger than that radiated only from the fault itself （EF）, especially for the shallow reverse faulting. In convention, EF is commonly used in the estimation of earthquake energy radiation. However, when the fault depth H, the distance between the free surface and top of fault location, increases, the effect of the coupling interaction between the fault and free surface decreases gradually. Therefore, the total radiated energy ER approaches to the EF when the depth H is about 2 times the fault length L The current study could provide us a partial explanation of the apparent stress discrepancy observed at the far field and near field in the recent large earthquake. Moreover, the current study also has a significant implication of how to quantitatively describe the near fault strong ground motion and associated seismic hazard from the earthquake source energy point of view.     

河岸带研究现状与存在问题探讨

论述了河岸带的定义、河岸植被带的结构与功能,探讨了国内外河岸带研究的现状,分析了当前研究中存在的问题,并对河岸带的研究进行了展望。     

电弧阴极区性质的研究

采用一维非平衡等离子体模型讨论了阴极区的等离子体性质 ,阴极区被分为电离区和空间电荷区 .数值计算结果表明 :在电离区 ,电子的能量由焦耳热提供 ,而离子的能量主要通过离子电子碰撞获得 ,空间电荷区的电位降约为 5 .4V .     

梅河三井放顶煤综采覆岩破坏观测成果分析

本文针对梅河三井１１０７放顶煤综采区地质采矿条件．在采区开采后获得的实际观测资料基础上．进行理论分析．得到了综放采区冒落裂缝带最大高度的计算公式．     

铸轧区长度的确定

本文对原冷凝区长度公式作了修正,并建立了总铸轧区长度的计算式。理论公式的正确性得到了实验验证。     

大别山东缘郯庐断裂带早期韧性剪切带的形成温度

年龄的解释强烈依靠于构造热事件的发生温度和矿物的封闭温度,在缺少构造热事件的温度资料的情况下,很难对年龄数据做出正确合理的解释。文章利用白云母-绿泥石地质温度计,计算了大别山东缘郯庐早期左旋走滑韧性剪切带的形成温度,获得了350～450℃的温度区间,并且多数温度值位于430～450℃之间。该温度值大于40Ar/39Ar法中白云母的封闭温度,从而由主要以残斑形式存在的白云母获得的年龄值记录了郯庐断裂带的活动时间,190Ma左右的白云母年龄值为接近于韧性剪切带变形年龄的冷却年龄。并由此年龄和温度数据得出郯庐断裂带形成于大别造山带造山作用后期。该韧性剪切带形成温度明显低于所叠加的造山带高角闪岩相变质岩,也指示为造山后期走滑运动的结果。     

D32海洋平台用钢在浪溅区腐蚀行为

通过极化实验和阻抗实验研究了D32海洋平台用钢在浪溅区的腐蚀规律,并利用扫描电镜和能量色散谱仪分析了各钢样的腐蚀产物. 结果表明,腐蚀产物的形貌成分和覆盖度的不同导致了模拟全浸区腐蚀速率稍大于钢样在海水中的腐蚀速率,模拟浪溅区腐蚀速率远大于模拟全浸区钢样腐蚀速率. 钢样在青岛海水、埕岛海水的全浸区和浪溅区的Nyquist图中出现的韦伯阻抗是由于表面形成的锈层及钙镁层所致.     

中小城市中心商业区内部空间结构探析--以盐城市为例

以盐城市中心商业区为例,研究了现阶段中小城市中心商业区内部空间结构特征及其形成过程与机制.揭示了在商业区发展变化中,不同等级类型商业网点更替的"过滤性".根据商业空间结构的形成机制,如:聚集作用、关联效应、商业地租、城市规划引导及城市整体消费情况等,选择合适的商业网点的区位,找到合理的商业网点之间及商业点与其它城市职能单位之间的空间搭配关系,可使商业区内部空间结构合理化,商业区整体经济效益最优.     

论北秦岭加里东期造山作用

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广西气候带的划分

根据有关文献和气候资料的分析，将广西划分为３个气候带：中亚热带、南亚热带和北热带。以稳定通过１０℃的积温为指标，稳定通过１０℃的积温８０００℃可以作为北热带与南亚热带的分界线；而积温６９００℃则可以作为南亚热带与中亚热带的分界线。根据这一指标，广西北热带北界大约经过防城港市的那酮北、马路北、防城港、北海市的北海北、山口北一线；南亚热带北界从贺州市信都附近经平南北、武宣、宾阳、上林、马山、都安、巴马