多层电流片中双撕裂模的耦合

应用边界层理论研究了多层电流片中m≥2的双撕裂模的耦合发展行为．在一阶近似下,解析求得了环位形中撕裂模的外区匹配参数Δ,所得结论对撕裂模的线性和非线性发展均有意义．结果表明,两有理面模之间的耦合总是使双撕裂模更不稳定．耦合的强度不仅与两有理面之间的距离和平衡状态有关,而且与模在两有理面发展的相对强弱有关．两有理面相距愈远,耦合相对愈弱;发展强的有理面处的模对另一有理面处的模影响更大．本文用所得结论对双撕裂模的初始非统性发展行为进行了分析．多层电流片中撕裂模不稳定性引起的自发重朕,可能对太阳耀斑、日冕加热、太阳风和磁层耦合等有重要影响．     

龙陵-澜沧断裂带双震型强震活动破裂模型讨论

龙陵地震和澜沧－耿马地震是龙陵－澜沧断裂带上两次典型的双震型强震活动,但它们在地质构造背景、应力场分布、发震构造和烈度分布等方面却具有截然不同的特点。龙陵地震发生在主要由花岗岩构成的地块内,地质构造比较均一;地震处在ＮＮＷ向挤压的统一应力场中;两主震的发震构造走向和两个Ⅸ度区长轴近于直交。澜沧－耿马地震发生在一古板块边界附近,震区构造复杂,耿马７．２级地震和澜沧７．６级地震发生于不同的应力环境中,发震构造和极震区长轴近于平行,呈斜列状分布。通过对龙陵地震和澜沧－耿马地震的对比分析,提出了双震型强震活动的共轭型和牵动型两种破裂模型,并对各自的特点及形成条件进行了初步分析     

西太平洋副热带高压双脊线及其对1998年夏季长江流域“二度梅”的影响

利用NCEP/NCAR再分析资料、日本气象厅提供的TBB资料研究了 1 998年 7月西太平洋副热带高压突然偏南的原因。结果表明 ,西太平洋副高脊线突然“南撤”有其一定局限性 ,事实上应是副热带高压脊线在南侧的一次“重建”过程。针对这次重建 ,发现 1 998年 7月上中旬在西太平洋副热带地区存在南北两个高压脊 ,据此本文提出了副热带高压双脊线的概念 ,并着重揭示了这次西太平洋副热带高压双脊线的基本演变特征、环流场和温湿场结构、可能的形成机制及其对 1 998年夏季长江流域“二度梅”的影响。分析表明西太平洋副热带高压双脊线时期具有与单脊线时期明显不同的环流特征和温湿场结构 ,其北侧脊线附近的特征与传统上单脊线副热带高压的特征较一致 ,但南侧脊线附近则更多的具有低纬度系统的特点 ;这次双脊线过程与赤道缓冲带北上并与副热带高压打通合并变性及热带对流云团的演变有密切关系。此外 ,文中还通过中国台站降水资料探讨了副热带高压双脊线的维持对中国东部雨型的影响 ,指出西太平洋副热带高压双脊线的出现改变了原有的水汽输送路径 ,从而在中国东部出现两条雨带 ,呈倒 7字型 ,分别与副热带高压北、南侧脊线相对应。这些结果为西太平洋副热带高压演变规律和机制的研究提供了新的线索     

Stresses along the metastable wedge of olivine in a subducting slab: possible explanation for the Tonga double seismic layer

A numerical calculation of the stresses associated with changes in volume during phase transitions of olivine in a descending slab results in a double layer of high shear stress along the metastable olivine wedge in the depth range 350-460 km. Stress in the upper layer is in-plane tensional and stress in the lower layer is down-dip compressional. The modeled stress field agrees with observations of stress in the Tonga double seismic zone. High shear stress also exists in the slab at depths below the metastable wedge. This stress distribution involves down-dip compression and trench-parallel tension, which agrees with about half of the focal mechanisms in the Tonga slab at depths of 460-690 km. The model supports the idea that at least two possible stress release mechanisms for deep earthquakes may act in the Tonga subducting slab. One, transformational faulting, is restricted to the metastable wedge while the other one acts below the metastable wedge.     

Localized stirring in a field of salt-fingers

In a series of laboratory experiments, a partially mixed patch was produced in thick linear concentration gradients favorable to salt-finger convection. Salt-fingers, which give rise to an up-gradient flux of buoyancy, can reduce and invert the density gradient in the initial imposed patch. This leads to overturning convection within the patch if (a) the ratio of ambient T and S gradients, R_ρ=αT_z/βS_z, is near one; (b) the initial imposed turbulence results in a nearly well-mixed patch; and (c) the patch thickness is large enough that convective eddies are able to transport T and S faster than salt-fingers. Once overturning occurs, subsequent turbulent entrainment can lead to growth of the patch thickness. Experimental results for one-dimensional patches (layers) agree well with the theoretical prediction. This thickening is in contrast to the collapse that a partially mixed three-dimensional patch would experience due to lateral intrusion in a wide tank.     

A Direct Inverse Model to Determine Permeability Fields from Pressure and Flow Rate Measurements

The determination of the permeability field from pressure and flow rate measurements in wells is a key problem in reservoir engineering. This paper presents a Double Constraint method for inverse modeling that is an example of direct inverse modeling. The method is used with a standard block-centered finite difference method. With an a priori grid block permeability field as input, two forward runs are made: the first is constrained with the measured pressures; the second is constrained with the measured flow rates. We calculate the pressures in the grid block centers from the first run, while from the second run we calculate the fluxes through the faces between the grid blocks. Substitution of these pressures and fluxes into Darcy’s law then yields the transmissibilities at the faces and hence the permeabilities in the grid blocks. In this way the “hard” data (measured pressures and flow rates) are always honored while the “soft”, geological data can be incorporated at the discretion of the geologist. Using a synthetic example, we demonstrate the method and compare the results with another method: Ensemble Kalman Filtering. The two methods agree within the scope of their applicability. The Double Constraint method focuses initially on determining spatial distributions of the permeability field for single-phase, steady state flow. For history matching an extension is required to non-steady state, two-phase flow conditions, which is already possible with EnKF. We are currently investigating the possibility of combining the two methods, whereby the strengths of the two methods could be fully exploited.     

四川木里小震群活动特征研究

本文通过对四川木里地区地震震源位置的重新确定,反演了地震震源机制解,结果显示:1重定位后的小震群震中分布成带状,地震震源深度分布在0—12km范围内;2经过对震群空间分布进行仔细分析,认为其发震构造是小金河断裂西侧的一条NWW向分支断裂;33次4.0级以上地震震源参数存在明显差异,浅源逆冲事件表现出受垂直方向应力(重力)作用的特征,走滑事件表现出与区域应力构造活动有关。     

2014年云南鲁甸MS6.5地震序列的双差定位

本文采用双差定位方法对云南鲁甸M_S6.5地震震后16天的地震序列进行重定位研究.重定位结果显示,主震位于27.11°N,103.35°E,震源深度约15 km;地震序列主要呈“L”形优势分布,分为SSE向和近EW向两支,并均呈现近垂直的震源分布特征,显示此次地震为走滑型,并存在两个不同方向的破裂面.虽然此次地震发生于NE向昭通断裂及其反冲断裂（龙树断裂、大岩洞断裂）附近,但这些断裂均为逆冲型断裂,被排除了作为发震断裂的可能性;鲁甸地震发生在呈放射性分布的多条断裂的交汇部位,SSE向破裂分支与包谷垴断裂的方向一致,近EW向破裂分支与小河断裂南端的走向一致. 鲁甸地震可能已将包谷垴断裂和小河断裂在深部贯通.     

Lattice-Preferred orientations of olivine in subducting oceanic lithosphere derived from the observed seismic anisotropies in double seismic zones

Subduction zones can generally be classified into Mariana type and Chilean type depending on plate ages,plate thicknesses, subduction angles, back-arc deformation patterns, etc. The double seismic zones(DSZs) in subduction zones are mainly divided into type I and type II which, respectively, correspond to the Mariana type and Chilean type in most cases. Seismic anisotropy is an important parameter characterizing the geophysical features of the lithosphere, including the subduction zones,and can be described by the two parameters of delay time dt and fast wave polarization direction /. We totally collected 524 seismic anisotropy data records from 24 DSZs and analyzed the statistical correlations between seismic anisotropy and the related physical parameters of DSZs.Our statistical analysis demonstrated that the fast wave polarization directions are parallel to the trench strike with no more than 30° for most type I DSZs, while being nearlyperpendicular to the trench strike for type II DSZs. We also calculated roughly linear correlations that the delay time dt increases with dip angles but decreases with subduction rates. A linear equation was summarized to describe the strong correlation between DSZ's subduction angle aDSZ and seismic anisotropy in subduction zones. These results suggest that the anisotropic structure of the subducting lithosphere can be described as a possible equivalent crystal similar to the olivine crystal with three mutually orthogonal polarization axes, of which the longest and the second axes are nearly along the trench-perpendicular and trench-parallel directions, respectively.     

Dynamic Changes of Sediment Discharge and the Influencing Factors in the Yellow River,China, for the Recent 90 Years

The dynamic changes in the sediment discharge over 90 years from 1919 to 2008 in the Yellow River in China were assessed on the basis of annual rainfall series and annual sediment series in Shan County hydrological station. The key factors affecting sediment discharge, such as rainfall, and human activities were studied. Anomaly accumulation method and double mass curve were employed to test the stage changes of sediment discharge, and to determine the main factors of sediment decline. Results showed that the annual average sediment discharge under natural conditions was about 16 × 10⁸ t, but the measured annual average sediment during 1919–2008 was 12.71 × 10⁸ t. The highest annual average during the study period was 39.10 × 10⁸ t in 1933 while the lowest was 1.77 × 10⁸ t in 2008. Sediment discharge in the Yellow River experienced two low sediment stages (1924–1931 and 1979–2008) and a high sediment stage (1932–1971), respectively. Since 1979, there was a significant decreasing trend in the sediment discharge, and the main influencing factor was fierce human activities. Annual average sediment discharge in the post‐development period (1979–2008) was 69.7% lower than that in the pre‐development period (1919–1978), with average reduction of 81 and 19% caused by human activities and rainfall, respectively. These results provide important evidence for making protecting policy for water resources quality and environmental safety of the Yellow River.