Outlier detection algorithms and their performance in GOCE gravity field processing

The satellite missions CHAMP, GRACE, and GOCE mark the beginning of a new era in gravity field determination and modeling. They provide unique models of the global stationary gravity field and its variation in time. Due to inevitable measurement errors, sophisticated pre-processing steps have to be applied before further use of the satellite measurements. In the framework of the GOCE mission, this includes outlier detection, absolute calibration and validation of the SGG (satellite gravity gradiometry) measurements, and removal of temporal effects. In general, outliers are defined as observations that appear to be inconsistent with the remainder of the data set. One goal is to evaluate the effect of additive, innovative and bulk outliers on the estimates of the spherical harmonic coefficients. It can be shown that even a small number of undetected outliers (<0.2 of all data points) can have an adverse effect on the coefficient estimates. Consequently, concepts for the identification and removal of outliers have to be developed. Novel outlier detection algorithms are derived and statistical methods are presented that may be used for this purpose. The methods aim at high outlier identification rates as well as small failure rates. A combined algorithm, based on wavelets and a statistical method, shows best performance with an identification rate of about 99%. To further reduce the influence of undetected outliers, an outlier detection algorithm is implemented inside the gravity field solver (the Quick-Look Gravity Field Analysis tool was used). This results in spherical harmonic coefficient estimates that are of similar quality to those obtained without outliers in the input data.     

西藏地区旱涝等级划分及时空分布特征

利用西藏22个站点1969-1998年逐日降水资料，采用d指数旱涝等级方法。按夏季（5-9月），初夏（5-6月），盛夏（7-8月）时段进行了旱涝等级划分。采用EOF分析方法对全区22个站点旱涝等级展开分解，得出西藏地区的旱涝时空分布特征，主要类型和周期，而且对西藏地区夏季（5-9月）的旱涝做了预测。     

舞阳、襄城盐湖盆地未熟-低熟油成藏模式

舞阳、襄城凹陷下第三生活费为膏、盐岩相盐湖沉积。半咸水-咸水湖相、盐湖相是形成未熟-低熟油的良好环境，沉积旋回中期断坳式沉积形成了主要油源层系，其高丰度未熟烃类推岩体是形成未熟-低熟油藏的物质基础，中-高孔、中-高渗碎屑岩层构成了未熟-低熟油藏的重要储集层，并发育了较好的生储盖组合，这些有利条件为舞阳、襄城凹陷形成未熟-低熟油藏提供了重要保证。指出凹陷陡坡带为背斜、断鼻型油藏分布区，还可能有混合型油藏；中部洼陷带为岩性油藏、裂隙型油藏发育区；斜坡带主要发育断鼻型油藏。     

论三维等时线叠加反偏移中的有关问题

利用几何射线理论和一种考虑了积分域边缘贡献的二维稳想法，研究了三维等时线叠加反偏移中的反偏移场，反偏移加权函及反偏移孔径。结果证明，在有限孔径条件下，反偏移场的结构比已发表的结果要复杂和多。即使在最简单的条件下，反偏移场也是由反偏移信号的反偏移噪声（孔径效应）叠加而成的。而且，反偏移场的结构强烈地依赖于反偏移孔径边缘的位置。为了消除孔径效应，应采用最佳反偏移孔径和针对有限孔径的加权函数。根据定义，最佳反偏移孔径为稳相点的第一和第二Fresnel区之和。在第一Fresnel区内，有限孔径和加权函数与文献中所给出的加权函数完全一致。而在第二Fresnel区内，有限孔径加权函数为常规的加权函数与一窗函数的乘积。在反偏移孔径的边缘上，有限孔径加权函恒取零值。     

Anatomy of shelf deltas at the edge of a prograding Eocene shelf margin, Spitsbergen

Abstract Although shelf‐edge deltas are well‐imaged seismic features of Holocene and Pleistocene shelf margins, documented outcrop analogues of these important sand‐prone reservoirs are rare. The facies and stratigraphic architecture of an outcropping shelf‐edge delta system in the Eocene Battfjellet Formation, Spitsbergen, is presented here, as well as the implications of this delta system for the generation of sand‐prone, shelf‐margin clinoforms. The shelf‐edge deltas of the Battfjellet Formation on Litledalsfjellet and Høgsnyta produced a 3–5 × 15 km, shelf edge‐attached, slope apron (70 m of sandstones proximally, tapering to zero on the lower slope). The slope apron consists of distributary channel and mouth‐bar deposits in its shelf‐edge reaches, passing downslope to slope channels/chutes that fed turbiditic lobes and spillover sheets. In the transgressive phase of the slope apron, estuaries developed at the shelf edge, and these also produced minor lobes on the slope. The short‐headed mountainous rivers that drained the adjacent orogenic belt and fed the narrow shelf, and the shelf‐edge position of the discharging deltas, made an appropriate setting for the generation of hyperpycnal turbidity currents on the slope of the shelf margin. The abundance of organic matter and of coal fragments in the slope turbidites is consistent with this notion. Evidence that many of the slope turbidites were generated by sustained turbidity currents that waxed then waned includes the presence of scour surfaces and thick intervals of plane‐parallel laminae within turbidite beds in the slope channels, and thick spillover lobes with repetitive alternations of massive and flat‐laminated intervals. The examined shelf‐edge to slope system, now preserved mainly below the shelf break and dominated by sediment gravity‐flow deposits, has a threefold stratigraphic architecture: a lower, progradational part, in which the clinoforms have a slight downward‐directed trajectory; a thin aggradational zone; and an upper part in which clinoforms backstep up onto the shelf edge. A greatly increased density of erosional channels and chutes marks the regressive‐to‐transgressive turnaround within the slope apron, and this zone becomes an angular unconformity up near the shelf edge. This unconformity, with both subaerial and subaqueous components, is interpreted as a sequence boundary and developed by vigorous sand delivery and bypass across the shelf edge during the time interval of falling relative sea level. The studied shelf‐margin clinoforms accreted mostly during falling stage (sea level below the shelf edge), but the outer shelf later became estuarine as sea level became re‐established above the shelf edge.     

Physical properties of ultrahigh-pressure metamorphic rocks from the Sulu terrain, eastern central China: implications for the seismic structure at the Donghai (CCSD) drilling site

About 30 samples representing major lithologies of Sulu ultrahigh-pressure (UHP) metamorphic rocks were collected from surface exposures and exploration wells, and compressional (Vp) and shear wave (Vs) velocities and their directional dependence (anisotropy) were determined over a range of constant confining pressures up to 600 MPa and temperatures ranging from 20 to 600 °C. Samples range in composition from acidic to ultramafic. P- and S-wave velocities measured at 600 MPa vary from 5.08 to 8.64 km/s and 2.34 to 4.93 km/s, respectively. Densities are in the range from 2.60 to 3.68 g/cm³. To make a direct tie between seismic measurements (refraction and reflection) and subsurface lithologies, the experimental velocity data (corresponding to shallow depths) were used to calculate velocity profiles for the different lithologies and profiles of reflection coefficients at possible lithologic interfaces across the projected 5000-m Chinese Continental Scientific Drilling Program (CCSD) crustal segment. Comparison of calculated in situ velocities with respective intrinsic velocities suggests that the in situ velocities at shallow depths are lowered by an increased abundance of open microcracks. The strongly reflective zone beneath the Donghai drill site can be explained by the impedance contrasts between the different lithologies. Contacts between eclogite/peridotite and felsic rocks (gt-gneiss, granitic gneiss), in particular, may give rise to strong seismic reflections. In addition, shear-induced (lattice preferred orientation (LPO)-related) seismic anisotropy can increase reflectivity. For the explanation of the high velocity bodies (>6.4 km/s) around 1000 m and below 3200-m depth, large proportions of eclogite/peridotite (about 40 and 30 vol.%, respectively) are needed.     

Structure sismique du socle paléozoı̈que du bassin des Doukkala,Môle côtier,Maroc occidental. Indication en faveur de l'existence d'une phase éo-varisqueSeismic structure of the Doukkala basin,Palaeozoic basement,western Morocco: a hint for an Eovariscan fold-and-thrust belt

Seismic profiles and well data from the Doukkala basin unravel the structure of the Palaeozoic basement and suggest that this coastal zone of western Morocco was affected by a compressive phase during the Frasnian. This resulted in the formation of upright, plurikilometric folds associated with reverse faults (North Doukkala), and of asymmetrical folds associated with mostly west verging ramps (South Doukkala). Folding involved all pre-Upper Frasnian formations and caused partial or total hiatus of Upper Frasnian–Strunian strata. This event can be correlated with the orogenic phase reported from more internal domains of the Morocco Hercynian belt, where it is referred to as the ‘Bretonne’ or ‘Eovariscan’ phase. To cite this article: H. Echarfaoui et al., C. R. Geoscience 334 (2002) 13–20     

分形在地貌学中应用的几个问题的分析

就实际地貌分形研究工作中经常遇到的截面约定、自仿射分形局域维与渡越长度、分维的比较以及过渡分形等几个问题进行了分析和探讨，并提出了在应用过程中的注意事项和解决方案。     

EXPERIMENTAL AND FIELD STUDY ON MINING-PIT MIGRATION

1 INTRODUCTION Because of the large quantity of sand and gravel in their beds, rivers have always been considered as a major source of sand and gravel for civil works. Acceptable quality, ease of extraction and economy are some of the reasons could be mentioned. Unfortunately, specific laws and regulations regarding the safe in-stream mining have not been provided for users and officials. What should be taken into account are the effects of over-mining of sand and gravel, which can cause …     

Reconstruction of the diagenesis of the fluvial-lacustrine- deltaic sandstones and its influence on the reservoir quality evolution-- Evidence from Jurassic and Triassic sandstones, Yanchang Oil Field, Ordos Basin

The reservoir quality of Jurassic and Triassic fluvial and lacustrine-deltaic sandstones of the Yanchang Oil Field in the Ordos Basin is strongly influenced by the burial history and facies-related diagenetic events. The fluvial sandstones have a higher average porosity (14.8%) and a higher permeability (12.7×10?3 ?m2) than those of the deltaic sandstones (9.8% and 5.8 ×10?3 ?m2, respectively). The burial compaction, which resulted in 15% and 20% porosity loss for Jurassic and Triassic sandstones, respectively, is the main factor causing the loss of porosity both for the Jurassic and Triassic sandstones. Among the cements, carbonate is the main one that reduced the reservoir quality of the sandstones. The organic acidic fluid derived from organic matter in the source rocks, the inorganic fluid from rock-water reaction during the late diagenesis, and meteoric waters during the epidiagenesis resulted in the formation of dissolution porosity, which is the main reason for the enhancement of reservoir-quality.