Morphological and microtectonic analysis of Quaternary deformation from Puná and Santa Clara Islands, Gulf of Guayaquil, Ecuador (South America)

This paper presents the neotectonic study of Santa Clara and Puná Islands sited in the Gulf of Guayaquil eastern part. Both islands are located on the south-western segment of the fault zone bounding to the east the North Andean Block. Fault motion and morphostructural analysis were carried out from Pleistocene age terrain. A two step deformation characterises the South Puná tectonics. The first step involves the Zambapala Cordillera uplift that post-dates Pleistocene sediments and pre-dates a marine terrace correlated with the M.I.S. 11 or 13 (440–550 ka). The second step is the formation of a pull-apart that shows evidence of 2.9 km dextral offset since the M.I.S. 11 or 13, giving an offset mean rate of 5.3 to 6.6 mm/yr. This rate is higher than the one calculated on the Pallatanga Fault northeast of the study area, in the Western Andean Cordillera, suggesting that deformation is split in different fault segments from the Gulf of Guayaquil to the continent. The Zambapala Cordillera uplift and transpression deformation requires a compressive event that may have been induced by the subduction process during the early Pleistocene.     

归一化总水平导数法在位场数据解释中的应用

本文提出归一化总水平导数法,通过对总水平导数进行空间归一化计算实现了异常体水平位置和深度的估计,此外还推导出基于归一化总水平导数的欧拉反褶积法来估算地下地质体的空间位置,两种方法反演结果的相互验证可有效地提高反演结果的可信度.理论模型试验证明空间归一化总水平导数法和归一化总水平导数欧拉反褶积法均能有效地完成异常体的水平位置和深度的估计,所获得的位置参数与理论值相一致.在利用归一化总水平导数法进行磁异常解释时,对数据进行化磁极计算可得到更加准确的结果.将其应用于实际航磁数据的解释,获得了岩脉的大致分布特征.     

重力场向下延拓Milne法

重力场向下延拓能够突出局部和浅部的异常信息,分离叠加的异常特征.但是向下延拓通常具有过程不稳定、下延深度小、结果不准确等问题.针对向下延拓所存在的不足,本文利用重力场及其垂向一阶导数,基于辛普森（Simpson）求积公式,推导出重力场向下延拓米尔尼（Milne）公式.将本文向下延拓方法应用于模型数据,向下延拓模型结果及误差曲线表明,相对于向下延拓快速傅里叶变换（FFT）法和积分迭代法,向下延拓Milne法的深度更大,相对误差更小;相对模型值,向下延拓Milne法能够获得稳定且准确的结果.对加拿大乃查科（Nechako）盆地地区实测航空重力数据进行本文方法向下延拓验证,处理结果表明,相对于实测异常,本文方法向下延拓结果能够很好还原实测数据,并且在进一步向下延拓中反映原始异常的趋势,增强局部和细小异常信息.

     

Transtensional folding

Strain modeling shows that folds can form in transtension, particularly in simple shear-dominated transtension. Folds that develop in transtension do not rotate toward the shear zone boundary, as they do in transpression; instead they rotate toward the divergence vector, a useful feature for determining past relative plate motions. Transtension folds can only accumulate a fixed amount of horizontal shortening and tightness that are prescribed by the angle of oblique divergence, regardless of finite strain. Hinge-parallel stretching of transtensional folds always exceeds hinge-perpendicular shortening, causing constrictional fabrics and hinge-parallel boudinage to develop.These theoretical results are applied to structures that developed during oblique continental rifting in the upper crust (seismic/brittle) and the ductile crust. Examples include (1) oblique opening of the Gulf of California, where folds and normal faults developed simultaneously in syn-divergence basins; (2) incipient continental break-up in the Eastern California-Walker Lane shear zone, where earthquake focal mechanisms reflect bulk constrictional strain; and (3) exhumation of the ultrahigh-pressure terrain in SW Norway in which transtensional folds and large magnitude stretching developed in the footwall of detachment shear zones, consistent with constrictional strain. More generally, folds may be misinterpreted as indicating convergence when they can form readily in oblique divergence.     

GPS广播星历参数拟合算法的探讨

介绍了全球定位系统(GPS)的广播星历参数拟合算法,在推导卫星位置对GPS广播星历参数偏导数的基础上,导出了调和项对偏导数的影响函数。计算结果表明,考虑调和项并不能提高GPS广播星历参数拟合的精度和效率,实际应用时应忽略调和项的影响。     

Non-Fickian mass transport in fractured porous media

The paper provides an introduction to fundamental concepts of mathematical modeling of mass transport in fractured porous heterogeneous rocks. Keeping aside many important factors that can affect mass transport in subsurface, our main concern is the multi-scale character of the rock formation, which is constituted by porous domains dissected by the network of fractures. Taking into account the well-documented fact that porous rocks can be considered as a fractal medium and assuming that sizes of pores vary significantly (i.e. have different characteristic scales), the fractional-order differential equations that model the anomalous diffusive mass transport in such type of domains are derived and justified analytically. Analytical solutions of some particular problems of anomalous diffusion in the fractal media of various geometries are obtained. Extending this approach to more complex situation when diffusion is accompanied by advection, solute transport in a fractured porous medium is modeled by the advection-dispersion equation with fractional time derivative. In the case of confined fractured porous aquifer, accounting for anomalous non-Fickian diffusion in the surrounding rock mass, the adopted approach leads to introduction of an additional fractional time derivative in the equation for solute transport. The closed-form solutions for concentrations in the aquifer and surrounding rocks are obtained for the arbitrary time-dependent source of contamination located in the inlet of the aquifer. Based on these solutions, different regimes of contamination of the aquifers with different physical properties can be readily modeled and analyzed.     

重力异常垂向一阶导数的一种简便算法

利用拉格朗日插值导出了重力异常垂向一阶导数的计算公式，给出了地面以及地面之上不同高度的求导系数。该公式可以计算地面上的重力垂向一阶导数，还可以直接计算地面之上任意高度上的垂向一阶导数。鉴于该公式除系数不同外，与上延公式完全相同，因此，程序设计尤为简单。使用本公式对模型数据和实际资料进行了处理，证明了本算法的实用性。     

内蒙古翁公敖包航磁异常的推断与解释

文章对内蒙古四子王旗—土默特右旗中北部近年发现的翁公敖包航磁异常进行推断与解释,在对找矿有望的航磁异常进行筛选后,对翁公敖包航磁异常进行了野外地质-地球物理查证,确定异常为铁矿所致;采用向上延拓、垂向导数、斜导数及小波变换等方法对航磁异常进行数据转换处理,以获取铁矿体的横向及纵向分布信息,取得了较好的效果。