Composition and petrology of HED polymict breccias: The regolith of (4) Vesta

We have done petrologic and compositional studies on a suite of polymict eucrites and howardites to better understand regolith processes on their parent asteroid, which we accept is (4) Vesta. Taking into account noble gas results from companion studies, we interpret five howardites to represent breccias assembled from the true regolith: Elephant Moraine (EET) 87513, Grosvenor Mountains (GRO) 95535, GRO 95602, Lewis Cliff (LEW) 85313, and Meteorite Hills (MET) 00423. We suggest that EET 87503 is paired with EET 87513, and thus is also regolithic. Pecora Escarpment (PCA) 02066 is dominated by melt‐matrix clasts, which may have been formed from true regolith by impact melting. These meteorites display a range in eucrite:diogenite mixing ratio from 55:45 to 76:24. There is no correlation between degree of regolith character and Ni content. The Ni contents of howardite, eucrite, and diogenites (HEDs) are mostly controlled by the distribution of coarse chondritic clasts and metal grains, which in some cases resulted from individual, low‐velocity accretion events, rather than extensive regolith gardening. Trace element compositions indicate that the mafic component of HED polymict breccias is mostly basalt similar to main‐group eucrites; Stannern‐trend basaltic debris is less common. Pyroxene compositions show that some trace element‐rich howardites contain abundant debris from evolved basalts, and that cumulate gabbro debris is present in some breccias. The scale of heterogeneity varies considerably; regolithic howardite EET 87513 is more homogeneous than fragmental howardite Queen Alexandra Range (QUE) 97001. Individual samples of a given howardite can have different compositions even at roughly 5 g masses, indicating that obtaining representative meteorite compositions requires multiple or large samples.     

高强度模拟酸雨量对珠三角地区潮土中重金属元素释放的影响

采用平均离子强度下30年雨量的模拟酸雨淋滤珠江三角洲潮土,电感耦合等离子体质谱法测定重金属元素,研究潮土0~90 cm处各节土壤柱中重金属镉、钴、铜、锌、铅、砷、钛、钒、铬、锰等元素的释放情况。研究表明,在高强度模拟酸雨淋滤下,潮土中重金属元素的释放情况存在较大差异。长期的酸雨淋滤,土壤中的镉、钴、铜、锌和铅在不同深度均有不同程度的淋失;砷、钛、钒、铬、锰等元素不会造成大量的淋失。利用这种差异可以评估重金属元素对环境的潜在影响,为农田生态系统的预警预测提供依据。     

Stationary phase approximation in the ambient noise method revisited

The method of extracting Green's function between stations from cross correlation has proven to be effective theoretically and experimentally.It has been widely applied to surface wave tomography of the crust and upmost mantle.However,there are still controversies about why this method works.Snieder employed stationary phase approximation in evaluating contribution to cross correlation function from scatterers in the whole space,and concluded that it is the constructive interference of waves emitted by the scatterers near the receiver line that leads to the emergence of Green's function.His derivation demonstrates that cross correlation function is just the convolution of noise power spectrum and the Green's function.However,his derivation ignores influence from the two stationary points at infinities,therefore it may fail when attenuation is absent.In order to obtain accurate noise-correlation function due to scatters over the whole space,we compute the total contribution with numerical integration in polar coordinates.Our numerical computation of cross correlation function indicates that the incomplete stationary phase approximation introduces remarkable errors to the cross correlation function,in both amplitude and phase,when the frequency is low with reasonable quality factor Q.Our results argue that the distance between stations has to be beyond several wavelengths in order to reduce the influence of this inaccuracy on the applications of ambient noise method,and only the station pairs whose distances are above several (5) wavelengths can be used.     

2020年1月16日库车MS5.6地震前库尔勒地震台部分资料异常特征

2020年1月16日新疆库车县发生MS5.6地震,地震发生后对库尔勒地震台部分资料出现的中短期异常进行识别分析.得出,地震发生前"库米什地震窗"ML≥1.0级地震月频次出现高值异常,库尔勒台尾波持续时间比值、尾波衰减系数、周期比值出现低值异常,库尔勒台时间扫描计算AC值、A(b)值、P(b)值、最小二乘法b值等4个参数...     

Seismic Wave Propagation and Excitation in Multi-layered Media with Irregular Interfaces Part (Ⅰ): SH Case

Study of seismic wave excitation and propagation in laterally heterogeneous media was an active and important subject in seismology in the past two decades, numerous analytical and numerical efforts have been made in this research field. In this article, I have, first, made a brief review on those developments and then introduced and summarized a unified and efficient method, global generalized reflection-transmission (abbreviated to R/T thereafter) matrices method, for synthetic seismograms in multi-layered media with irregular interfaces developed by the author [24~26]. As demonstrated in this article, this method could be regarded as an extension of the generalized R/T coefficients method for the horizontally layered case [2,5] to the layered media with irregularly shaped interfaces by incorporating the T matrices technique [27,28]. Because of the use of a recursive scheme in computing the global generalized R/T matrices, this method is efficient, particularly for the case with a large number of irre     

南昌市厚田沙地蔓荆灌丛沙堆的形态与沉积特征

为探究亚热带湿润地区河湖周边发育的灌丛沙堆形态与沉积特征,以南昌市厚田沙地为研究区,对其优势种蔓荆（Vitex trifolia）所形成的灌丛沙堆开展野外调查,通过对不同部位的沉积物进行采样与分析,研究沙堆形态、沉积特征及其与植被特性之间的关系。结果表明：蔓荆灌丛沙堆形态大多为盾形,水平尺度大,高度矮,坡度缓。沙堆沉积物以中沙为主,分选性较差,呈正偏和窄峰态分布,沙源来自附近平沙地和丘间地,为近源沉积。平均粒径从迎风坡底部至背风坡底部呈现为先变细后变粗的趋势,体现了灌丛沙堆的防风滞沙功能和对沙粒的重新分选作用。灌丛与沙堆的各形态参数（灌丛高度除外）均存在高度的正相关性（P＜0.01）,说明各形态参数在沙堆发育过程中得以协调发展。受植被类型和区域环境的影响,与干旱-半干旱地区直立生长且分支少的灌丛形成的椭球形或圆锥形沙堆形态不同,蔓荆匍匐生长且高度较矮的形态常形成低矮且范围较大的灌丛沙堆。亚热带湿润地区风力资源不丰富及厚田沙地沙源不足使沉积物主要来源于附近平沙地与丘间地,但不同坡位沉积规律与干旱-半干旱地区相同。     

Analytical and Numerical Modeling of a Double Well Capture Zone

Closed-form steady-state analytical solutions for capture times are derived considering both pumping–injecting and pumping–pumping double-well systems. Numerical simulations are used to obtain capture times and the numerical results agree with analytical solutions. The influences of regional flows upon the capture zones are analyzed numerically. In a heterogeneously stratified aquifer, the mean and the variance of the capture time are calculated. It is found that hydraulic conductivity distribution plays an important role in determining the mean and the variance of the capture time.     

钻井柱状图可视化查询系统的设计与实现

钻井柱状图是石油行业勘探开发最常用的一种图件。为了开发出灵活通用的钻井柱状图制作软件,为可视化分析提供良好基础,提出了“两库四类三层”系统设计方案,应用COM思想和模板定制技术,采用C#．net语言从底层进行了软件实现,所开发的软件模块具备一定的独立性和较好的通用性。     

半潮堤前的反射形态与时均流速场分析

采用模型试验和数值模拟研究了不同水深工况下半潮堤前的反射形态及时均流速场。基于Hilbert变换建立了叠合波的时频分离技术,同时获取了入射波和反射波的波面过程及相位关系,通过试验数据证明其适用于不同反射程度的波浪信号分析。不同水深工况下,半潮堤前形成了部分立波系统,腹点和节点分别以四分之一波长的偶数倍和奇数倍交替增加。半潮堤前底床水质点水平速度包络图与波面包络图相差四分之一周期的相位,水平速度的极大值和极小值分别出现在波面包络图的节点和腹点,意味着节点处易形成冲刷,腹点处易形成淤积。3种工况的周期平均速度场均在迎浪基床上方的堤脚处存在一个小型环流系统,可能引起局部冲刷,此处需加强防护。淹没工况下,半潮堤前的周期平均速度场形成一个大型环流系统,表层水流向堤后,中下层水流向海侧,意味着底床悬起的泥沙很可能向离岸方向流失。     

南海輓近海平面变化与构造升降初步研究

揭示南海輓近海平面变动和古岸线诸多遗迹,探讨晚更新世以来海平面变化一般规律,初步分析南海周缘中全新世和现代地壳构造升降速率,得出本区海平面上升率适中参考值为0.10—2.0mm/a,初步估算未来50年内海平面变化趋势在1.26—4.0mm/a之间;而构造升降受块断差异运动控制,一般规律是南海北部沿岸自东向西递减,由福建南部1.15mm/a至海南岛南部0.54mm/a。近代地壳形变资料亦证实这种变化规律。