The potential impact of bedform migration on seagrass communities in Torres Strait,northern Australia

Seagrass communities in the northwest of Torres Strait are known to disappear episodically over broad areas. Sediment mobility surveys were undertaken within two study areas during the monsoon and trade wind seasons, in the vicinity of Turnagain Island, to find out if the migration of bedforms could explain this disappearance. The two study areas covered sand bank and sand dune environments to compare and contrast their migration characteristics. Repeat multibeam sonar surveys were used to measure dune-crest migration during each season.     

Double parameterized regularization inversion method for migration velocity analysis in transversely isotropic media with a vertical symmetry axis

Simultaneous estimation of velocity gradients and anisotropic parameters from seismic reflection data is one of the main challenges in transversely isotropic media with a vertical symmetry axis migration velocity analysis. In migration velocity analysis, we usually construct the objective function using the l₂ norm along with a linear conjugate gradient scheme to solve the inversion problem. Nevertheless, for seismic data this inversion scheme is not stable and may not converge in finite time. In order to ensure the uniform convergence of parameter inversion and improve the efficiency of migration velocity analysis, this paper develops a double parameterized regularization model and gives the corresponding algorithms. The model is based on the combination of the l₂ norm and the non‐smooth l₁ norm. For solving such an inversion problem, the quasi‐Newton method is utilized to make the iterative process stable, which can ensure the positive definiteness of the Hessian matrix. Numerical simulation indicates that this method allows fast convergence to the true model and simultaneously generates inversion results with a higher accuracy. Therefore, our proposed method is very promising for practical migration velocity analysis in anisotropic media.     

衰减雷达波有限元偏移

高频雷达波在地球介质中有较强的衰减,反演中不可忽略．为此文中首先给出了含衰减项的雷达波的有限元方程及其偏移理论．用有限差分法或有限元法可正演合成雷达波资料,加入一定的扰动后用含衰减项的雷达波有限元方程做偏移,实例结果表明,考虑衰减项的偏移结果能使界面更好地归位,这为提高探地雷达地质解释的分辨率提供了可能性,为逐渐地实现符合雷达波自身动力学特点的处理系统奠定了基础．     

基于梯度平方结构张量算法的高密度二维立体层析反演

射线参数水平分量是立体层析数据空间中最为重要的参数信息,梯度平方结构张量算法是一种针对图像的边缘检测快速算法.本文将叠前地震数据集视为图像,将梯度平方结构张量算法用于射线参数水平分量的提取,提高了立体层析数据空间的准备效率.高效率的数据空间提取使得高密度立体层析反演成为可能,数据空间加密后的立体层析反演精度以及叠前深度成像质量相比常规流程得到明显提高.基于二维理论数据与南海某二维深水数据的严格测试证实了该方法的有效性与稳健性.     

再论地震数据偏移成像

利用地震波正向传播方程对属于波形线性反演问题近似求解方法的地震数据偏移成像进行重新推导,得到了适合散射地震数据的散射偏移成像方法和适合反射地震数据的反射偏移成像方法.以地震波传播的散射理论为出发点,首先根据描述一次散射波正向传播的线性方程研究建立散射地震数据的偏移成像方法理论;利用高频近似对产生散射波场的地下速度扰动函数的空间变化进行近似,推导出地下反射率函数,再由散射波传播方程推导出基于反射率函数的反射波传播方程,然后根据描述一次反射波正向传播的线性方程研究建立反射地震数据的偏移成像方法理论.本文指出和修正了Claerbout偏移成像方法中的不足,提出的地震数据偏移成像方法是对当前偏移成像方法理论的完善,使反射地震数据偏移成像具有了更坚实的数学物理理论基础,得到的偏移成像结果相位正确、位置准确、分辨率提高.     

等价各向异性介质一阶拟声波 方程正演模拟及其效率分析

为克服各向异性弹性波动方程正演模拟的局限,本文研究了各向异性介质拟声波方程的交错网格有限差分数值解法.首先,从VTI介质胡克定律和qP-qSV波频散关系两种思路出发,通过声假设近似,给出了两种不同形式的VTI介质一阶拟声波方程,并通过引入波场的伪速度分量,推导了一种新的VTI介质一阶应力-速度方程,并通过旋转坐标系将其推广到TTI介质中;其次,构造了一阶拟声波方程的交错网格高阶有限差分格式,并推导了相应的PML边界条件;最后,对本文方法中固有的qSV人为干扰波的产生机制和压制方法进行了简单讨论.数值结果表明:3种一阶拟声波方程在运动学和动力学上是等价的,相对于各向异性弹性波正演模拟,其节省了内存,提高了计算效率;各向异性因素会影响反射波旅行时和振幅等波场特征,在后续的处理、反演和解释中不可忽略;VTI介质HESS模型的逆时偏移结果也验证了本文方法的合理性.      

Charging of oil fields surrounding the Shaleitian uplift from multiple source rock intervals and generative kitchens,Bohai Bay basin,China

This paper discusses origin and charging directions of oil fields on the Shaleitian Uplift, Bohai Bay basin. The Shaleitian Uplift is a footwall uplift surrounded by three sags containing mature source rocks. The origins of the four oil fields on the Shaleitian Uplift, both in terms of source rock intervals and in terms of generative kitchens, were studied using biomarker distributions for 61 source rock samples and 27 oil samples. Hierarchical cluster analysis using 12 parameters known to be effective indicators of organic matter input and/or depositional conditions allowed the identification of six oil types or classes. These six oil classes could then be linked to three distinct source rock intervals ranging in age from 43.0 Ma to 30.3 Ma. The third member (43.0–38.0 Ma in age) and first member (35.8–32.8 Ma) of the Eocene Shahejie Formation, and the third member of the Oligocene Dongying Formation (32.8–30.3 Ma) each sourced one class of oil. The other three classes represent mixtures of oil generated from multiple source rock intervals. Traps on the Shaleitian Uplift were charged in the east by oil generated from the Eocene Shahejie Formation in the Bozhong Sag, in the southeast by oil generated from the Eocene Shahejie and then Oligocene Dongying formations in the southwestern part of the Bozhong Sag and/or in the eastern part of the Shanan Sag, and in the southwest by oil generated from the Eocene Shahejie Formation in the western part of the Shanan Sag. The estimated migration distances range from less than 5 km to about 20 km. The compositional heterogeneity within fields and multiple-parameter comparisons between oils from nearby wells in different fields have proven to be a powerful tool to determine the in-filling histories of oil fields in cases where multiple source rock intervals and multiple generative kitchens exist.     

2005年江西晚稻飞虱大发生气象成因初步分析

介绍了江西省稻飞虱历年发生概况,以及2005年江西稻飞虱发生特点,并从2005年副高脊线位置与飞虱早迁、汛期降雨峰值与飞虱多迁、台风环流与飞虱秋季回迁、夏秋季温湿条件与飞虱生长繁殖的关系等方面,进行了稻飞虱大发生的气象成因分析,力图为今后建立稻飞虱发生发展气象预测模型,开展灾害监测与预报提供依据.分析结果表明,2005年江西省晚稻飞虱具有发生时间早、面积广、为害重等特点,为历史罕见大爆发;稻飞虱主要来源于外地迁入,有春季迁入及秋季回迁2种;副高脊线位置偏南,西南气流强盛,导致春季气候适宜,暖湿气流活跃,强降水多,有利春季稻飞虱早迁、多迁、大量迁,早稻发生后的残留虫量是晚稻飞虱大发生的虫源基础;7～10月台风频频影响江西,特别是后期台风的影响,加速了秋季稻飞虱随东北气流的回迁,为晚稻飞虱大爆发起到促进作用;盛夏不热且秋季不凉的气象条件,有利于当地稻飞虱的生长繁殖,导致飞虱代数多.     

Modelling sand wave migration in shallow shelf seas

Sand waves form a prominent regular pattern in the offshore seabed of sandy shallow seas. The positions of sand-wave crests and troughs slowly change in time. Sand waves are usually assumed to migrate in the direction of the residual current. This paper considers the physical mechanisms that may cause sand waves to migrate and methods to quantify the associated migration rates. We carried out a theoretical study based on the assumption that sand waves evolve as free instabilities of the system. A linear stability analysis was then performed on a 2DV morphological model describing the interaction between the vertically varying water motion and an erodible bed in a shallow sea. Here, we disrupted the basic tidal symmetry by choosing a combination of a steady current (M₀) and a sinusoidal tidal motion (M₂) as the basic flow. We allowed for two different physical mechanisms to generate the steady current: a sea surface wind stress and a pressure gradient. The results show that similar sand waves develop for both flow conditions and that these sand waves migrate slowly in the direction of the residual flow. The rates of migration and wavelengths found in this work agree with theoretical and empirical values reported in the literature.     

Speciation of Trace Elements in Acidic PoreWaters from Waste Rock Dumps by Ultrafiltration andIon Exchange Combined with ICPMS and ICPOES

A speciation procedure developed on reactive acidicpore water samples from mining areas is presented.Methods with low consumption of solution are requiredthat allow rapid sample preparation to avoid equilibriumchanges as far as possible. The entire procedure includesonly three parallel separation steps. One aliquot is filteredthrough an 1 kd ultrafiltration membrane to separate traceelements adsorbed or complexed by colloids. One cationand one anion exchange are performed with two additionalaliquots to determine simple hydrated ions and smallinorganic complex ions. Commonly used procedures ofion exchange seem to be problematic. This new techniqueis based on a novel ion exchanger. Subsequently the threefractions obtained from the separation procedures and theoriginal pore water sample are analysed by ICPMS, ICPOES,ET-AAS, Flame-AAS, FES and IC to determine the concentrationsof the major ions and additionally up to 50 trace elements. Theinfluence of pH-values and several dissolved compounds iscontrolled in experiment series with synthetically preparedsolutions to reveal potential artifacts.