Process-based modeling of the overflow-induced growth of erosional channels

A new process-based approach is introduced for a more efficient computation of the overflow-induced growth of an erosional channel in a non-cohesive homogeneous narrow landmass such as the breach growth in a sand-dike. The approach is easy to incorporate in a 1D/2DV morphodynamic model to compute the channel growth both vertically and laterally.     

热带地区碳酸盐岩上覆红色风化壳的成因机理及元素演化

开展热带岩溶地区红色风化壳元素地球化学演化规律研究,有助于丰富碳酸盐岩风化成土理论的认识。在越南北部选取典型的碳酸盐岩风化剖面,分析热带气候条件下碳酸盐岩上覆红色风化壳中主量元素的物质来源和演化特征。结果表明:无论Ti/Zr的元素比值分析,Hf-Zr、Nb-Ta及Sm-Nd的元素对协变分析,还是上地壳元素平均值(UCC)标准化分析,两个剖面的上覆风化壳均显示原地残积的特征,即两个剖面是碳酸盐岩的原位风化产物。碳酸盐岩风化成土过程中,CaO、MgO淋失明显,Al_2O_3和Fe_2O_3发生富集,显示两个剖面均经历较强的风化过程,但是白云岩和灰岩剖面有一定的分异特征。越南北部白云岩风化剖面从基岩到上部土层显示出稳定的Ti-Fe元素共富集特征,而灰岩剖面中Fe的增长速率明显超过Ti。白云岩上覆风化壳经历了强烈的风化作用,其脱硅作用弱于灰岩风化剖面,而富集铝的作用强于灰岩。迁移系数的演化规律说明两个剖面中长石成分(钾长石、钠长石等)或次生矿物(伊利石等)在风化成土过程中逐渐分解,同时Al、Fe、Si等稳定元素的在风化剖面中不断富集。     

Stanniferrous granites of Vietnam: Rb-Sr and Ar-Ar isotope age,composition, sources,and geodynamic formation conditions

Doklady Earth Sciences - Stanniferrous granite-leucogranite massifs in Vietnam to which the bedrock and placer commercial deposits of cassiterite are associated (Timtuc etc.) are of late Cretaceous...     

Simple monitoring method for precaution of landslides watching tilting and water contents on slopes surface

A low-cost and simple monitoring method for early warning of landslides is proposed. To detect abnormal deformation of a slope, this method employs a tilt sensor in place of an extensometer on the slope surface. In order to examine the relevance of measuring rotation angle on a slope surface by tilt sensor, model tests were conducted, and rotation on the slope surface was observed together with slide displacement along the surface. The rotation data responded 30 min before failure in a model test, which could be useful as a signal for early warning. However, the behavior of rotation before failure varies from case to case, and thus, criteria to issue warning should be defined more carefully. For a model slope made of uniform loose sand, measurement of slide displacement along the slope surface is sensitive to failure at the toe, while the measurement of rotation on the slope surface is useful to detect the development of progressive failure upward along the slope. Wireless sensor units with microelectromechanical systems (MEMS) tilt sensor and volumetric water content sensor were also examined on a real slope in Kobe City, and a long-term monitoring was attempted. A simple but possible way to define the criteria of judgment to issue warning can be proposed based on combination of data obtained by the tilt sensors and volumetric water content sensors.     

Reply to Comment by Z. Şen,İ. Sönmez,and H. Tatli

Mathematical Geosciences -     

Tectonic wedging along the rear of the offshore Taiwan accretionary prism

The structural geometry, kinematics and density structure along the rear of the offshore Taiwan accretionary prism were studied using seismic reflection profiling and gravity modeling. Deformation between the offshore prism and forearc basin at the point of incipient collision, and southward into the region of subduction, has been interpreted as a tectonic wedge, similar to those observed along the front of mountain ranges. This tectonic wedge is bounded by an east-dipping roof thrust and a blind, west-dipping floor thrust. An east-dipping sequence of forearc-basin strata in the hanging wall of the roof thrust reaches a thickness in excess of 4 km near the tip of the interpreted tectonic wedge. Section restoration of the roof sequence yields an estimate of 4 km of shortening, which is small compared with that inferred in the collision area to the north, based on the variation in distance between the apex of the prism and the island arc.Previous studies propose that either high-angle normal faulting or backfolding has exhumed the metamorphic rocks along the eastern flank of the Central Range in the collision zone on land. To better constrain the initial crustal configuration, we tested 350 crustal models to fit the free-air gravity anomaly data in the offshore region to study the density structure along the rear of the accretionary prism in the subduction and initial collision zones before the structures become more complex in the collision zone on land. The gravity anomaly, observed in the region of subduction (20.2°N), can be modeled with the arc basement forming a trenchward-dipping backstop that is overlain by materials with densities in the range of sedimentary rocks. Near the point of incipient collision (20.9°N), however, the free-air gravity anomaly over the rear of the prism is approximately 40 mgal higher, compared with the region of subduction, and requires a significant component of high density crustal rocks within the tectonic wedge. These results suggest that the forearc basement may be deformed along the rear of the prism, associated with the onset of collision, but not in the subduction region further to the south.     

龙门山构造带区域稳定性探讨

根据龙门山构造带的地震地质特征、地震活动规律及新构造活动特征,综合分析认为该地区区域稳定性受控于龙门山断裂带。而断裂带又以韧性切变形为主,蠕滑运动为特征,决定该带在相当长的一段时间内,发生强烈地震的可能性不大。     

分散元素的超常富集与共生

本以地质事实为基础,初步探讨了分散元素的超常富集和共生问题。在一定地质条件下,分散元素可以发生超常富集,乃至形成分散元素的独立矿床。低温条件有利于分散元素的超常富集和形成独立矿物;热水沉积作用在某些分散元素的成矿过程中具有重要意义。分散元素共生,是一种常见的现象。相似的地球化学性质和地球化学行为,是导致分散元素共生的基本原因。男外,区域地质背景也是一个重要因素。     

固结问题有限元法时步自适应研究

关于提高有限元法解的精度和稳定性问题已受到不少学者的重视。基于Biot固结理论,为提高有限元法计算的精度和稳定性,研究了固结过程中的时步自适应。采用基本原理推导出时步控制公式,从而全面控制应力和孔隙压力场。研究结果有助于准确模拟应力应变的发展,对粘土心墙土石坝等建筑物的设计及施工有重要意义。