Pore-water geochemistry in methane-seep sediments of the Makran accretionary wedge off Pakistan: Possible link to subsurface methane hydrate

Cold seeps are pervasive along the continental margin worldwide,and are recognized as hotspots for elemental cycling pathway on Earth.In this study,analyses of pore water geochemical compositions of one-400 cm piston core(S3) and the application of a mass balance model are conducted to assess methane-associated biogeochemical reactions and uncover the relationship of methane in shallow sediment with gas hydrate reservoir at the Makran accretionary wedge off Pakistan.The results revealed that approximately 77% of sulfate is consumed by the predominant biogeochemical process of anaerobic oxidation of methane.However,the estimated sulfate-methane interface depth is-400 cm below sea floor with the methane diffusive flux of 0.039 mol/(m~2·a),suggesting the activity of methane seepage.Based on the δ~(13)C_(DIC) mass balance model combined with the contribution proportion of different dissolved inorganic carbon sources,this study calculated the δ~(13)C of the exogenous methane to be-57.9‰,indicating that the exogenous methane may be a mixture source,including thermogenic and biogenic methane.The study of pore water geochemistry at Makran accretionary wedge off Pakistan may have considerable implications for understanding the specific details on the dynamics of methane in cold seeps and provide important evidence for the potential occurrence of subsurface gas hydrate in this area.     

Controlling factors on the charging process of oil and gas in the eastern main sub-sag of the Baiyun Sag,Zhujiang River (Pearl River) Mouth Basin

The eastern main sub-sag (E-MSS) of the Baiyun Sag was the main zone for gas exploration in the deep-water area of the Zhujiang River (Pearl River) Mouth Basin at its early exploration stage, but the main goal of searching gas in this area was broken through by the successful exploration of the W3-2 and H34B volatile oil reservoirs, which provides a new insight for exploration of the Paleogene oil reservoirs in the E-MSS. Nevertheless, it is not clear on the distribution of “gas accumulated in the upper layer, oil accumulated in the lower layer” (Gas_upper-Oil_lower) under the high heat flow, different source-rock beds, multi-stages of oil and gas charge, and multi-fluid phases, and not yet a definite understanding of the genetic relationship and formation mechanism among volatile oil, light oil and condensate gas reservoirs, and the migration and sequential charge model of oil and gas. These puzzles directly lead to the lack of a clear direction for oil exploration and drilling zone in this area. In this work, the PVT fluid phase, the origin of crude oil and condensate, the secondary alteration of oil and gas reservoirs, the evolution sequence of oil and gas formation, the phase state of oil and gas migration, and the configuration of fault activity were analyzed, which established the migration and accumulation model of Gas_upper-Oil_lower co-controlled by source and heat, and fractionation controlled by facies in the E-MSS. Meanwhile, the fractionation evolution model among common black reservoirs, volatile reservoirs, condensate reservoirs and gas reservoirs is discussed, which proposed that the distribution pattern of Gas_upper-Oil_lower in the E-MSS is controlled by the generation attribute of oil and gas from source rocks, the difference of thermal evolution, and the fractionation controlled by phases after mixing the oil and gas. Overall, we suggest that residual oil reservoirs should be found in the lower strata of the discovered gas reservoirs in the oil-source fault and diapir-developed areas, while volatile oil reservoirs should be found in the deeper strata near the sag with no oil-source fault area.     

利用GPS拖体在万山区域测量平均海面技术研究

Wanshan area has been chosen to be the specified field to calibrate and validate(Cal/Val) the HY-2 altimeter and its follow-on satellites. In March 2018, an experiment has been conducted to determine the sea surface height(SSH) under the HY-2 A ground track(Pass No. 203). A GPS towing-body(GPS-TB) was designed to measure the SSH covering an area of about 6 km×28 km wide centered on the HY-2 A altimeter satellite ground track. Three GPS reference stations, one tide gauge and a GPS buoy were placed in the research area, in order to process and resolve the kinematic solution and check the precision of the GPS-TB respectively. All the GPS data were calculated by the GAMIT/GLOBK software and TRACK module. The sea surface was determined by the GPS-TB solution and the tide gauge placed on Zhiwan Island. Then the sea surface of this area was interpolated by Arc GIS10.2 with ordinary Kriging method. The results showed that the precision of the GPS-TB is about 1.10 cm compared with the tide gauge placed nearby, which has an equivalent precision with the GPS buoy. The interpolated sea surface has a bias of –1.5–4.0 cm with standard deviation of 0.2–2.4 cm compared with the checking line. The gradient of the measured sea surface is about 1.62 cm/km along the HY-2 orbit which shows a good agreement compared with the CLS11 mean sea surface(MSS). In the Cal/Val of satellites, the sea surface between the tide gauge/GPS buoy and the footprint of altimeter can be improved by this work.     

Quantifying bank storage of variably saturated aquifers

Numerical simulations were conducted to quantify bank storage in a variably saturated, homogenous, and anisotropic aquifer abutting a stream during rising stream stage. Seepage faces and bank slopes ranging from 1/3 to 100/3 were simulated. The initial conditions were assumed steady-state flow with water draining toward the stream. Then, the stream level rose at a constant rate to the specified elevation of the water table given by the landward boundary condition and stayed there until the system reached a new steady state. This represents a highly simplified version of a real world hydrograph. For the specific examples considered, the following conclusions can be made. The volume of surface water entering the bank increased with the rate of stream level rise, became negligible when the rate of rise was slow, and approached a positive constant when the rate was large. Also, the volume decreased with the dimensionless parameter M (the product of the anisotropy ratio and the square of the domain's aspect ratio). When M was large (>10), bank storage was small because most pore space was initially saturated with ground water due to the presence of a significant seepage face. When M was small, the seepage face became insignificant and capillarity began to play a role. The weaker the capillary effect, the easier for surface water to enter the bank. The effect of the capillary forces on the volume of surface water entering the bank was significant and could not be neglected.     

时域反射仪（TDR）测定土壤含水量标定曲线评价与方案推荐

时域反射仪（Time Domain Reflectometry）可用于室内和田间快速、 准确、 自动测定土壤含水量, 是目前应用最广泛的土壤含水量测定方法之一。适宜的土壤含水量标定曲线（即土壤表观介电常数和土壤含水量之间的关系）是TDR准确测定土壤含水量的关键。目前文献中存在大量的土壤含水量标定曲线, 但尚未有研究对这些标定曲线进行系统的验证和分析评价。因此, 它们的准确性和适用范围尚不明晰, 严重影响到与土壤含水量测定相关的研究。通过查阅大量国内外文献, 收集整理了一系列土壤含水量标定曲线的经验公式（19个）和半经验半物理模型（5个）, 并利用大量的文献实测数据对其进行综合评价。同时运用均方根差（RMSE）, 平均误差（AD）, 纳什效率系数（NSE）等三个指标对比分析和评价这些标定曲线的准确性和可靠性。研究结果表明： 经验公式中Topp、 Roth（1992）2、 Jacobosen、 Yoshikawa2、 Alharathi模型和半经验模型中Malicki1公式及其修订模型综合性能较好。研究成果可为利用TDR准确测定土壤含水量及土壤含水量标定曲线的选择提供参考和指导。     

基于混合回归模型的夏季高温日数预测

本文以变化比较激烈的高温日数为对象,通过加权叠加、周期波动以及尺度比较等理论分析提出一种短期气候预测观点,即长周期波动可用当地前期各种气象要素的长周期波动的某种函数表示,而短周期波动依然与大范围周边环境因子的变化有关。采用功率谱分析、逐步回归、方差分析等常用统计手段和二项式平滑方法,建立长周期波动和波动偏差比的预报方程,在此基础上得到高温日数的预报方程。应用该方法对合肥地区的高温日数进行了预测试验,利用滚动预报得到13个预报样本。在13个试测样本中,有11个样本试测较为准确,试测准确率达到84．6％。在试测不准确的2个样本中,误差有5～6d,而且它们出现在高温日数相对较多的年份,因此试测效果令人满意。     

低温雨雪过程的粒子群-神经网络预报模型

利用逐日气温和降水量数据、NCEP/NCAR再分析资料以及预报场资料,通过分析提取我国南方区域持续性低温雨雪过程及其预报因子,使用粒子群-神经网络方法建立非线性的统计集合预报模型 (PSONN-EPM),对我国南方区域持续性低温雨雪过程进行预报试验。结果表明:以过程的冷湿程度及影响范围为标准,将低温雨雪过程分为一般过程和严重过程,并建立不同的预报模型效果较好。通过10 d独立样本预报试验看,基于粒子群-神经网络方法建立的集合预报模型比基于逐步回归方法建立的预报模型的预报平均相对误差小,对严重过程预报能力高于对一般过程预报,且这种非线性统计集合建模方法在建模过程中不需要调整神经网络参数,在实际预报业务中值得尝试。     

遥感技术在地质灾害调查及灾害规律研究中的应用——以辽宁省建昌县为例

地质灾害与地质环境条件、人类工程活动关系密切,严重威胁着人类生命财产安全,制约社会经济的可持续发展。运用遥感技术对辽宁省建昌县进行地质灾害调查,利用ENVI5.3软件对高分二号数据进行预处理,建立遥感解译标志并开展了野外验证,最终解译滑坡、崩塌、泥石流、地面塌陷等地质灾害点75个;同时,利用Arcgis10.4空间分析功能,对遥感解译地质灾害点与地貌、坡度、坡向、构造、水系及人类工程活动等因子进行叠加分析,基本查清了研究区地质灾害规模、空间分布特征和发育规律,为研究总结区域上地质灾规律及有效预防提供了详实可靠的基础资料。     

Receiver function imaging in strongly laterally heterogeneous crust: Synthetic modeling of BOLIVAR data

We resolve a large (~20 km) discrepancy in Moho depth determined from PdS receiver functions (RFs) and from active source seismic profiling in the complex Caribbean-South American plate boundary zone in eastern Venezuela. As part of the BOLIVAR experiment 20 broadband stations were deployed along an active source profile to record teleseisms. Using the extremely heterogeneous crustal model obtained from active source data, we generated 2D finite-difference elastic wave synthetics and from them calculated receiver functions and CCP stacks. We compare the observations with synthetic sections that have been spatially sampled at 0.25 km to 40 km. The densely sampled synthetics show that several events in the field data that were originally interpreted as the Moho are multiple reflections within sedimentary basins. Where the Moho has the steepest dip under the plate boundary the CCP stacks fail to image the Moho well, regardless of the density of spatial sampling. A suitable spatial sampling criterion for clearly imaging the lower crust and Moho is to overlap Fresnel zones by 50% at Moho depth, which for the 1 Hz receiver functions examined here, requires an instrument spacing of 15–20 km, with the actual field data density ranging from 20 km to 100 km.