Seismic intensity distribution of shallow earthquakes due to rupture velocities and faulting modes

Isoseismals of seismic intensity distributions are represented by earthquake source size, faulting mode, and rupture velocity of fault propagation. Unilateral faulting forms egg—shaped isoseimals, while bilateral faulting forms elliptical ones. It is found that the ratio of major to minor axes of isoseismals is sensitive to rupture velocity. Rupture velocity, faulting mode, and fault trend have been determined from the seismic intensity maps of the 1964 Niigata and the 1983 Japan Sea earthquakes in China by matching theoretical isoseismals. Rupture velocities thus estimated are mostly 70% to 90% of shear wave velocity. The difference would be considered as follows: short—waves which determine the seismic intensity are strongly dependent on the rupture of small—scale fault heterogeneities and on the jerky—onsets and abrupt terminations of local rupture propagations. On the other hand, rupture velocity from long—waves represents an average rupture propagation along the whole fault length. Faulting mode and fault trend estimated from seismic intensity maps match with each earthquake faulting independently determined. This suggests that the present method would be applicable to some historical earthquakes with known seismic intensity distribution to obtain detailed information on the faulting process.     

Polymerization process of biopyribole in metasomatism at the Akatani ore deposit,Japan

Clinopyroxene transforms to triple chain silicate, double chain silicate (amphibole) and sheet silicate (talc) in the metasomatic process of the Akatani ore deposit. The triple chain silicate is contained in fibrous amphibole-like phase (“amphibole”). It is of electron microscopic size of 1,000 Å at maximum width in b-direction, and is a calciferous analogue of clinojimthompsonite. Various kinds of fine textures formed in metasomatic reaction process were found in clinopyroxenes. A large amount of triple chains and a small amount of double chains were transformed from single chains in the host clinopyroxene, maintaining topotactic relation. The kinetics of the structural change of biopyriboles at the Akatani ore deposit was discussed from the viewpoint of the mode of occurrence of triple and double chain silicates. The nucleation of triple chain structure slab with one triple chain width is apt to occur rather than the nucleation of double chain structure slab with width of two double chains in clinopyroxene host. Various fine textures in clinopyroxenes and amphibole-like phase were interpreted as corresponding to the propagation of metasomatic reactions.     

A scaling model for quantification of earthquakes in and near Japan

A simple method is developed to determine seismic moments of earthquakes. The method is qualified through criteria such as simplicity of calculations, coverage of wide magnitude range, and insensitivity to detailed instrumental response. The method is applied to 163 major earthquakes which occurred underneath Japan and the Japan Sea in the time from 1926 to 1977. Magnitudes of these earthquakes, which have been determined by the Japan Meteorological Agency, (M_JMA) cover the range from 4.3 to 7.5. At first, source spectra are analyzed through a very simple way introducing two new parameters: characteristic period T_c and seismic-moment factor M_c. The former is defined as an average value of apparent periods of seismic waves with the maximum trace amplitude at many stations. The latter is an average of products of maximum trace amplitude and its apparent period multiplied by epicentral distance. It is shown that T_c corresponds to the period of the corner frequency of an earthquake and M_c to the seismic-moment density at the period of T_c. A scaling model of earthquake source spectra is presented which satisfies the empirical relations between the surface-wave magnitude M_s and M_JMA, and M_JMA and the body-wave magnitude m_b. Those relations are independent of the Gutenberg and Richter relation between M_s and m_b, because M_JMA is determined from maximum amplitudes of seismic waves with a period of about 4 sec. The static seismic moment of each earthquake can be estimated from calculated M_c using the source spectra of the scaling model. Seismic moments of 18 earthquakes determined by conventional analyses from near- and/or far-field observations are consistent with static seismic moments thus estimated over the range from 2 × 10²³ to 3 × 10²⁷ dyne cm. This shows the potential in practice of the present method, especially in the routine processing of seismic data.     

Physical basis of earthquake magnitudes: an extreme value of seismic amplitudes from incoherent fracture of random fault patches

A relation between surface-wave magnitude M_s and fault area S for great earthquakes has been proposed

log S 2M_{s − 11.5 (}M_{s > 7.5)}

A similar formula has been also derived for body-wave magnitude m_b^* redetermined from maximum amplitudes of short-period P-wavetrains

log S ∝ 1.7 m_b^*

These are quite different from a theoretical relation expected on the basis of long-wave approximation. Because wavelengths of seismic waves used for the above magnitudes are very short compared to the size of earthquake sources, these relations represent the short-period nature of the earthquake process. The statistical theory of extreme values has been applied to understand the relations considering that the component waves which constitute the wavetrains for m_b^* and M_s determinations originate from the random fracture of fault heterogeneities.     

A Rb/Sr record of catchment weathering response to Holocene climate change in Inner Mongolia

Variation in the rubidium to strontium (Rb/Sr) ratio of the loess–palaeosol sequences has been proposed to reflect the degree of pedogenesis and weathering in the northwestern region of China. To characterize the Rb/Sr ratio of the dissolved loads of a single catchment, we analysed a 12·08 m sediment core from Daihai Lake in Inner Mongolia, north China. Dating control was provided by ²¹⁰Pb, ¹³⁷Cs and AMS‐¹⁴C. Sequential extraction experiments were conducted to investigate the concentrations of Rb and Sr on various chemical fractions in the lake sediments. Down‐core variation in the Rb/Sr ratios provides a record of Holocene weathering history. From 9 to 3·5 ka bp , accelerated chemical weathering was experienced throughout the Daihai catchment under mainly warm and humid conditions, and this reached a maximum at c. 5 ka bp . However, weathering was reduced between c. 8·25 and 7·90 ka bp , which may reflect the global 8·2 ka cooling event. After c. 2·5 ka bp , increased Rb/Sr ratios with higher frequency of fluctuations indicate reduced weathering within the Daihai catchment. The highest Rb/Sr ratios in the Little Ice Age lake sediments indicate the weakest phase of Holocene chemical weathering, resulting from a marked reduction in Sr flux into the basin. The Rb/Sr record also shows an enhancement of chemical weathering under today's climate, but its intensity is less than that of the Medieval Warm Period. Increased Rb/Sr in lake sediment corresponding to reduced catchment weathering is in striking contrast to Rb/Sr decrease in the glacial loess layers in the loess–palaeosol sequence. Copyright © 2005 John Wiley & Sons, Ltd.     

岩溶作用对任丘古潜山碳酸盐岩油藏赋存的控制作用

根据大量钻井及开发动态资料,研究了任丘古潜山雾迷山组白云岩岩溶发育牲特征对油藏赋存的控制作用。溶蚀孔洞是最重要的储集空间,岩溶不发育的泥质白云岩段的分隔作用,导致在全油田统一油水界面以下有残余油区赋存,古潜山面上的溶蚀残丘等局部高点是残余油赋存的有利地段。     

Intergranular trace elements in mantle xenoliths from Russian Far East: Example for mantle metasomatism by hydrous melt

Based on both major and trace element chemistry, the occurrence of the intergranular component in mantle-derived xenoliths from far eastern Russia has been constrained. Whole-rock trace element measurements of one xenolith show apparent negative anomalies in Ce, Th, and high field strength elements on normalized trace element patterns. The trace element pattern of the whole rock differs from those of constituent minerals, indicating that the anomalies in the whole rock are attributable to the presence of an intergranular component. That assumption was confirmed using in situ analysis of trace elements in the intergranular substance and melt inclusion using laser ablation inductively coupled plasma–mass spectrometry. Both the intergranular component and the melt inclusions have identical trace element patterns, which mean that these materials are a cognate metasomatizing agent. The anomalies are regarded as mantle metasomatism related to an aqueous fluid. Hydrous minerals were observed on the wall of the melt inclusions using micro-Raman spectroscopy, indicating that the melt inclusions contained a large amount of water. Thus, this study reveals a trace element composition of a hydrous metasomatizing agent in the mantle.     

Characterization of the amorphous state in metamict silicates and niobates by EXAFS and XANES analyses

X-ray absorption spectroscopy using synchrotron radiation has been applied to the investigation of the coordination geometries around Y, Zr and Nb atoms in metamict zircon, gadolinite, fergusonite, euxenite and samarskite. EXAFS and XANES spectra of their crystalline counterparts and synthetic compounds including ZrO₂, Y₂O₃, YNbTiO₆, YNbO₄, LiNbO₃, and NiNb₂O₆ were also measured for comparison. Metamict zircon shows a significant decrease in its Zr-O bond distances accompanying an increase in distortion of the Zr-O coordination polyhedra as compared with crystalline zircon. On the contrary, the average Nb-O bond distances and the symmetry of the coordination polyhedra around the Nb atoms in metamict euxenite and samarskite resemble those in the crystalline euxenite. Compared with crystalline fergusonite, a decrease in the distortion of the Nb-O octahedra is observed in metamict fergusonite. The structures of the second nearest neighbors (the metal-metal interactions) are largely disrupted in the metamict specimens except for metamict zircon and samarskite with high trivalent iron concentration. Nb in metamict samarskite is in octahedral coordination by oxygen and is similar to that in euxenite.     

CO2浓度梯度对两种岩溶微藻碳酸酐酶活性的影响

以经岩溶水驯化的小球藻（Chlorella vulgaris）和喜钙念珠藻(Nostoc calcicola Breb.)为实验对象,在封闭体系中用Willbur和 Anderson 方法比较研究两种不同微藻在不同CO2浓度下碳酸酐酶活性变化情况。结果表明:在低于3%CO2浓度的环境中岩溶微藻可通过快速调节自身碳酸酐酶活性来应对CO2升高带来的生境影响,在影响最大的2.5%的环境下小球藻与喜钙念珠藻碳酸酐酶活性分别提高了1.46倍和2.12倍;岩溶微藻应对CO2浓度增大带来的pH下降有着重要的恢复作用,随培养时间增长培养环境中的pH得到恢复;随着CO2浓度的增大,岩溶因子对碳酸酐酶有着重要的影响;培养48 h时Ca2+与喜钙念珠藻碳酸酐酶的相关性最高,而电导率（EC）与小球藻碳酸酐酶相关程度最高。