Structural evolution and the partitioning of deformation during basin growth and inversion: A case study from the Mizen Basin Celtic Sea,offshore Ireland

The Celtic Sea basins lie on the continental shelf between Ireland and northwest France and consist of a series of ENE–WSW trending elongate basins that extend from St George’s Channel Basin in the east to the Fastnet Basin in the west. The basins, which contain Triassic to Neogene stratigraphic sequences, evolved through a complex geological history that includes multiple Mesozoic rift stages and later Cenozoic inversion. The Mizen Basin represents the NW termination of the Celtic Sea basins and consists of two NE–SW-trending half-grabens developed as a result of the reactivation of Palaeozoic (Caledonian, Lower Carboniferous and Variscan) faults. The faults bounding the Mizen Basin were active as normal faults from Early Triassic to Late Cretaceous times. Most of the fault displacement took place during Berriasian to Hauterivian (Early Cretaceous) times, with a NW–SE direction of extension. A later phase of Aptian to Cenomanian (Early to Late Cretaceous) N–S-oriented extension gave rise to E–W-striking minor normal faults and reactivation of the pre-existing basin bounding faults that propagated upwards as left-stepping arrays of segmented normal faults. In common with most of the Celtic Sea basins, the Mizen Basin experienced a period of major erosion, attributed to tectonic uplift, during the Paleocene. Approximately N–S Alpine regional compression-causing basin inversion is dated as Middle Eocene to Miocene by a well-preserved syn-inversion stratigraphy. Reverse reactivation of the basin bounding faults was broadly synchronous with the formation of a set of near-orthogonal NW–SE dextral strike-slip faults so that compression was partitioned onto two fault sets, the geometrical configuration of which is partly inherited from Palaeozoic basement structure. The segmented character of the fault forming the southern boundary of the Mizen Basin was preserved during Alpine inversion so that Cenozoic reverse displacement distribution on syn-inversion horizons mirrors the earlier extensional displacements. Segmentation of normal faults therefore controls the geometry and location of inversion structures, including inversion anticlines and the back rotation of earlier relay ramps.     

Groups, algebras, and the non-linearity of geophysical inverse problems

Mathematical methods from the theory of continuous groups are used to determine whether a non-linear inverse problem, in the form of a functional, can be transformed into a linear inverse problem. If such transformations exist they can be constructed from the solutions of a linear system of differential equations. An illustration of the methodology is given by the linearization of the functional relating basement topography to observed surface gravity. The linearized inversion of gravity data for basement topography is applied to observations from Yucca Mountain, Nevada. A 2.0 km step in the basement to the west of Yucca Mountain, corresponding to the Bare Mountain fault, matches the Bouguer gravity anomaly. The resolution and uncertainty associated with the estimates of basement topography indicate that the structure directly beneath the gravity line is well constrained.     

A method of obtaining a velocity-depth envelope from wide-angle seismic data

Summary. Due to the non-uniqueness of traveltime inversion of seismic data, it is more appropriate to determine a velocity-depth ( v-z ) envelope, rather than just a v-z function. Several methods of obtaining a v-z envelope by extremal inversion have been proposed, all of which invert the data primarily from either x-p , or T-p , or both domains. These extremal inversion methods may be divided into two groups: linear extremal and non-linear extremal. There is some debate whether the linearized perturbation techniques should be applied to the inherently non-linear problem of traveltime inversion. We have obtained a v-z envelope by extremal inversion in T-p with the constraint that the inversion paths also satisfy x-p observations. Thus we use data jointly in r-p and x-p , and yet avoid the linearity assumptions.
This joint, non-linear extremal inversion method has been applied to obtain a v-z envelope down to a depth of about 30 km in the Baltimore Canyon trough using x-t data from an Expanding Spread Profile acquired during the LASE project. We have found that the area enclosed by the v-z envelope is reduced by about 15 per cent using x-p control on the T-p inversion paths, compared to the inversion without x-p control.     

An observational study of radiation temperature inversions in Fairbanks,Alaska

A series of high resolution radiosonde launches were conducted over seven case-study days spanning spring 2009 and fall/winter 2010 during clear and calm nights at Fairbanks, Alaska to evaluate the effects of solar radiation, snow covered surfaces and low-level winds on the formation and evolution of surface-based temperature inversions (SBI). Transition seasons were selected because strong nighttime radiation cooling allows well-defined inversions to form while sufficient daytime solar heating allows the observation of dissipation processes in the sub-arctic latitudes. During the fall/winter period, co-located Doppler phased array acoustic soundings (SODAR) were carried out. The height of the SBI retrieved by radiosonde and SODAR did not differ more than 50 m. However, the SODAR profiles display a much more complex structure in the atmospheric boundary layer. Observations during this experiment demonstrated that the formation of the SBI is initiated by a rapid cooling at the surface followed by a steady columnar cooling and subsequent growth of the SBI depth overnight.     

Statistical, geochemical, and morphological analyses of stone line formation in Uganda

The resolution of conflicting fluvial (allochthonic erosion and deposition) and bioturbation (autochthonic faunal turbation) theories of stone line formation has important implications for tropical geomorphology—with the former indicating dynamic, punctuated landscape development and the latter implying relative landscape stability with ongoing moderate erosion. On a gentle hill in central Uganda, we quantitatively characterized and statistically modeled gravel distributions for 93 profiles. Elemental analysis of K, selected rare-earth elements (REE) and appropriate index elements were employed to test for compositional differences between soils above and saprolite below hilltop stone lines. We also excavated and carefully described four indicative profiles. The results of this study were difficult to reconcile with the bioturbation theory of stone line formation. Important findings included (i) the lack of a consistent gravel-free biomantle with a weak connection between biomantle thickness and stone-line depth, (ii) highly variable stone line depth with a strong inverse relationship between stone line depth and maximum gravel content, (iii) unweathered and rounded cobbles in a stone line over saprolite with angular, highly weathered quartz, and (iv) a statistically significant geochemical difference between soils and saprolites, with evidence of a less weathered surface mantle over more weathered saprolite. These findings indicated a sedimentary origin for soils at this site—even for what is presently a flat, geomorphically isolated hilltop. Evidence from this study and previous work on the geochemistry of this site [Geochim. Cosmochim. Acta 67 (2003) 2711] suggests that the contemporary hilltop once occupied a lower landscape position.     

荒漠-绿洲交错带土壤N、P、K含量的高光谱反演模型

利用新疆奇台县荒漠-绿洲交错带的75个土壤样本,选取土壤可见光-近红外光谱的反射率（R）、光谱反射率倒数之对数（lg（1/R））、光谱反射率一阶导数（FDR）和光谱波段深度（Depth）4个指标,分析了其与土壤N、P、K元素含量的关系,分别建立了反演模型并对其精度进行了检验。结果表明：可见光-近红外反射光谱快速估算荒漠-绿洲交错带土壤N、P、K元素含量的潜力大,其预测精度由高到低的排列顺序为：N>P>K。不同光谱指标反演模型的精度各异,指标Depth和FDR的预测效果明显优于lg（1/R）和R,对N和P元素的拟合效果为：lg（1/R）相似文献   

广元市金洞乡Ⅱ号滑坡系统演化的非线性动力学反演分析

本文在研究广元市金洞乡Ⅱ号滑坡位移特征基础，认为该滑坡正处于开放的、复杂的非线性动力学系统中。在滑坡系统诸要素中，宝珠寺加水位的升降已成为系统演化的控制力量。坡体位移是系统演化的主要状态变量，但北部坡体、南部坡体与中部坡体之间的滑动变形具较强的独立性，单一的位移序列不能较好的反映滑坡的演化特征。因此，文中以两列独立的位序列为状态变量，结合控制变量建立了滑坡系统演化的非线性动力学模型，并从现有的变形监测滦资料进行滑坡系统的非线性力学反演和稳定学反演和稳定性评价。