汶川MS8.0级地震成因三“层次”分析——基于深部电性结构

2008年5月12日汶川M_S8级地震的发生不是局部地区孤立的构造事件,研究汶川地震的孕震机制,应该把局部分析和区域分析相结合,关注地壳上地幔直至地幔过渡带的深部结构.基于近年来在东北、华北和汶川地震附近地区进行的深部结构电磁探测结果,结合地震学等其他资料,从太平洋板块的俯冲、印度板块的碰撞和松潘甘孜地块的推挤三个“层次”探讨分析汶川特大地震的成因.太平洋板块向亚洲大陆的俯冲作用,导致中国大陆东部地幔过渡带深度较普遍地存在着停滞的板片,它对汶川地震的影响不可忽视.印度板块与青藏高原的碰撞,使组成高原的各地块发生向北和向东的运动,各地块向东的运动作用于南北地震带中南段,影响到该区域的地震活动.松潘甘孜地块向四川地块的推挤,使松潘甘孜地块运动方向和龙门山断裂带形成“丁”字形结构,龙门山断裂带显示为较陡直的电性边界,加剧了汶川地震前的应力积累,可能是汶川地震发生的最直接的诱因.     

汶川Ms8．0级地震成因三“层次”分析——基于深部电性结构

2008年5月12日汶川Ms8级地震的发生不是局部地区孤立的构造事件,研究汶川地震的孕震机制,应该把局部分析和区域分析相结合,关注地壳上地幔直至地幔过渡带的深部结构.基于近年来在东北、华北和汶川地震附近地区进行的深部结构电磁探测结果,结合地震学等其他资料,从太平洋板块的俯冲、印度板块的碰撞和松潘甘孜地块的推挤三个"层次"探讨分析汶川特大地震的成因.太平洋板块向亚洲大陆的俯冲作用,导致中国大陆东部地幔过渡带深度较普遍地存在着停滞的板片,它对汶川地震的影响不可忽视.印度板块与青藏高原的碰撞,使组成高原的各地块发生向北和向东的运动,各地块向东的运动作用于南北地震带中南段,影响到该区域的地震活动.松潘甘孜地块向四川地块的推挤.使松潘甘孜地块运动方向和龙门山断裂带形成"丁"字形结构,龙门山断裂带显示为较陡直的电性边界,加剧了汶川地震前的应力积累,可能是汶川地震发生的最直接的诱因.     

http://dx.doi.org/10.1016/j.gsf.2016.10.001

The Francevillian Group in Gabonese Republic was recently established as a typical sedimentary sequence for the Paleoproterozoic.However,its age is rather poorly constrained,mainly based on Rb-Sr and Nd-Sm datings.This study reports new zircon data obtained from Chaillu massif and N'goutou complex,which constrain the protolith age of the basement orthogneisses and the igneous age of an intrusive granite,respectively.Most zircons from the orthogneisses are blue and exhibit oscillatory zoning in cathode-luminescence images.Zircons with lower common lead abundances tend to be distributed close to the concordia curve.Two age clusters around 2860 Ma and 2910 Ma are found in zircons plotted on the concordia curve.Based on the Th/U ratios of zircons,these ages correspond to the protolith ages of the orthogneisses,and the zircons are not metamorphic in origin.Syenites and granites were collected from the N'goutou complex that intrudes into the FA and FB units of the Francevillian Group.The granitoids exhibit chemical composition of A-type granite affinity.Half of zircons separated from the granite are non-luminous,and the remaining half exhibit obscure internal textures under cathode-luminescence observation.All zircon grains contain significant amounts of common lead;the lead isotopic variability is probably attributed to the mixing of two components in the zircons.The zircon radiogenic ~(207)Pb/~(206)Pb ratio is 0.13707 ± 0.0010.corresponding to a ~(207)Pb/~(206)Pb age of 2191 ± 13 Ma.This constrains the minimum depositional age of the FA and FB units.Furthermore,the FB unit consists of manganese-rich carbonate rocks and organic carbon-rich black shales with macroscopic fossils.Based on our age constraints,these organisms appeared in the study area just after the last Paleoproterozoic Snowball Earth event,in concert with global scale oxidation event encompassing the Snowball Earth.     

How to use the groundwater resources at the area polluted by organoarsenic compounds for Old Japanese Army Toxic Gas Weapon in Japan

从医学地质学角度看,在日本地质污染的地方如何使用地下水资源,我们面临许多问题.本文讨论了地质污染学(geo-pollution science)作为医学地质学中一门学科的概念以及在受二苯亚砷酸污染的地方成功使用农业地下水的案例.     

Historical Auroras in the 990s: Evidence of Great Magnetic Storms

A significant carbon-14 enhancement has recently been found in tree rings for the year 994, suggesting an extremely strong and brief cosmic ray flux event. The origin of this particular cosmic ray event has not been confirmed, but one possibility is that it might be of solar origin. Contemporary historical records of low-latitude auroras can be used as supporting evidence of intense solar activity around that time. We investigate previously reported as well as new records that have been found in contemporary observations from the 990s to determine potential auroras. Records of potential red auroras in late 992 and early 993 were found around the world, i.e. in the Korean Peninsula, Saxonian cities in modern Germany, and the Island of Ireland, suggesting the occurrence of an intense geomagnetic storm driven by solar activity.     

Food sources of benthic animals on intertidal and subtidal bottoms in inner Ariake Sound,southern Japan,determined by stable isotopes

To evaluate the relative importance of possible food sources, including riverine particulate organic matter, reeds, benthic microalgae, seaweeds, cultured laver (Porphyra) and coastal phytoplankton, for commercial bivalves and co-occurring benthic animals, 73 macrofaunal species were collected from intertidal and subtidal soft bottoms in the inner part of Ariake Sound, Kyushu, southern Japan, and their isotopic compositions were analyzed. The results revealed that (1) both intertidal and subtidal food webs were constituted of 3 trophic levels, (2) suspension-feeding bivalves utilize a mixture of benthic microalgae and coastal phytoplankton, and omnivores and carnivores incorporate benthic microalgae and phytoplankton through their intermediate prey, and (3) 3 bivalves (Scapharca kagoshimensis, Modiolus metcalfei and Atrina lischkeana) inhabiting both intertidal and subtidal bottoms showed similar seasonal fluctuations, suggesting no difference in the diet composition among the species and between the 2 habitats. We conclude that a large biomass of benthic microalgae which was approximately equal to that of phytoplankton and the strong tidal currents that would resuspend benthic microalgae and transport them to subtidal bottom areas account for the benthic microalgal and phytoplankton based trophic structure in the inner part of Ariake Sound.     

Relationships of interannual variability in SST and phytoplankton blooms with giant jellyfish (Nemopilema nomurai) outbreaks in the Yellow Sea and East China Sea

Giant jellyfish (Nemopilema nomurai) outbreaks in relation to satellite sea surface temperature (SST) and chlorophyll-a concentrations (Chl-a) were investigated in the Yellow Sea and East China Sea (YECS) from 1998 to 2010. Temperature, eutrophication, and match–mismatch hypotheses were examined to explain long-term increases and recent reductions of N. nomurai outbreaks. We focused on the timing of SST reaching 15 °C, a critical temperature enabling polyps to induce strobilation and enabling released ephyra to grow. We analyzed the relationship of the timing with interannual variability of SST, Chl-a, and the timing of phytoplankton blooms. Different environmental characteristics among pre-jellyfish years (1998–2001), jellyfish years (2002–2007, 2009), and non-jellyfish years (2008, 2010) were assessed on this basis. The SST during late spring and early summer increased significantly from 1985 to 2007. This indicated that high SST is beneficial to the long-term increases in jellyfish outbreaks. SST was significantly lower in non-jellyfish years than in jellyfish years, suggesting that low SST might reduce the proliferation of N. nomurai. We identified three (winter, spring, and summer) major phytoplankton bloom regions and one summer decline region. Both Chl-a during non-blooming periods and the peak increased significantly from 1998 to 2010 in most of the YECS. This result indicates that eutrophication is beneficial to the long-term increases in jellyfish outbreaks. Timing of phytoplankton blooms varied interannually and spatially, and their match and mismatch to the timing of SST reaching 15 °C did not correspond to long-term increases in N. nomurai outbreaks and the recent absence.     

Effect of the development of notches and tension cracks on instability of limestone coastal cliffs in the Ryukyus, Japan

Notches cut by waves are currently developing at the base of vertical coastal limestone cliffs in Okinawa, Japan. The cliff height varies from 3.0–22.1 m, and the maximum notch depth is 8.8 m. Many rectangular or cubic blocks, which appear to have originated from cliff failures, are found on platforms in front of the cliffs. On the flat top surface of the cliff, tension cracks often run parallel to the cliff face. The vertical face of the cliffs displays small undulations but no sliding striation, suggesting that cliff failures have been caused by toppling rather than by shearing or sliding. We use slope stability analysis to determine the critical condition for toppling failure. Physical and mechanical properties of the cliff material were first obtained from laboratory tests. The results indicate that the strength of limestone shows a scale effect, such that the strength decreases with increasing size of the test specimens. Based on this result, we estimated the strength of a rock mass corresponding to the size of the coastal cliff. Cliff stability was then analyzed using a cantilever beam model. Comparison of the stability analysis and the dimension of fallen blocks indicates that toppling failure is strongly associated with the development of notches and tension cracks.     

船舶螺旋桨尾流场的数值分析

利用基于速度势的低阶面元法计算船舶螺旋桨的尾流场。采用计算较为简捷的关于扰动速度势的基本积分微分方程，并采用双曲面形状的面凶以消除面元间的缝隙。Newton-Raphson迭代过程被用来在桨叶随边满足压力Kutta条件，使桨叶面上表面的压力在随边有良好的一致性。在计算面元的影响系数时，应用了Morino导出的解析计算公式，加快了数值计算的速度。从解面元法的基本积分方程得到的偶极强度和源汇强度，直接求得尾流场的速度分布。