Post-mid-Cretaceous eastern North Sea evolution inferred from 3D thermo-mechanical modelling

The Late Cretaceous–Cenozoic evolution of the eastern North Sea region is investigated by 3D thermo-mechanical modelling. The model quantifies the integrated effects on basin evolution of large-scale lithospheric processes, rheology, strength heterogeneities, tectonics, eustasy, sedimentation and erosion.

The evolution of the area is influenced by a number of factors: (1) thermal subsidence centred in the central North Sea providing accommodation space for thick sediment deposits; (2) 250-m eustatic fall from the Late Cretaceous to present, which causes exhumation of the North Sea Basin margins; (3) varying sediment supply; (4) isostatic adjustments following erosion and sedimentation; (5) Late Cretaceous–early Cenozoic Alpine compressional phases causing tectonic inversion of the Sorgenfrei–Tornquist Zone (STZ) and other weak zones.

The stress field and the lateral variations in lithospheric strength control lithospheric deformation under compression. The lithosphere is relatively weak in areas where Moho is deep and the upper mantle warm and weak. In these areas the lithosphere is thickened during compression producing surface uplift and erosion (e.g., at the Ringkøbing–Fyn High and in the southern part of Sweden). Observed late Cretaceous–early Cenozoic shallow water depths at the Ringkøbing–Fyn High as well as Cenozoic surface uplift in southern Sweden (the South Swedish Dome (SSD)) are explained by this mechanism.

The STZ is a prominent crustal structural weakness zone. Under compression, this zone is inverted and its surface uplifted and eroded. Contemporaneously, marginal depositional troughs develop. Post-compressional relaxation causes a regional uplift of this zone.

The model predicts sediment distributions and paleo-water depths in accordance with observations. Sediment truncation and exhumation at the North Sea Basin margins are explained by fall in global sea level, isostatic adjustments to exhumation, and uplift of the inverted STZ. This underlines the importance of the mechanisms dealt with in this paper for the evolution of intra-cratonic sedimentary basins.     

井水位气压效率b值动态响应的断层-前兆场主应力组合模式

统计鲁03，04井流水作业闰的气压效率b值发现，在华北及其周缘绝大多数地震前两井前兆异常形态各异，经分析井孔定位断层走向与地震前兆场主应力的组合模式不同是产生上述现象的根本原因。     

半无限空间中圆形孔洞周围SH波的散射

建立了求解在含有圆形孔洞的弹性半空间中SH波散射与圆形孔洞附近动应力集中问题的解析方法。利用SH波散射的对称性和多极坐标的方法，构造了一个可以预先满足半空间自由表面上应力自由边界条件的圆形孔洞对SH波散射的波函数。利用这一波函数，则可将该问题转化成对一个圆形孔洞散射的求解问题。该问题的解答最终又可归结为对一组无究代数方程组的求解问题，并可利用截断有限项的方法对其进行计算，最后给出了有关圆形也洞附近动应力集中问题的算例和数值结果，并讨论了波数与圆孔至自由边界距离变化对动应力集中的影响。     

昆仑山口西8.1级地震前青海省形变及地温前兆特征分析

通过对青海省地倾斜、地应力、深井地温3种前兆手段在昆仑山口西8．1级地震前异常的分析与研究，得出了强地震远场前兆的一些初步特征，并与近场前兆异常特征做了比较，这对该省今后强震短期预报将是有益的。     

2000年4月29日内乡ML4.7级地震前潢川地电异常变化

2000年4月29日11时54分，河南省南阳市内乡县马山口镇与镇平县寺山乡之间发生一次ML4.7级地震。地震前3天，潢山台视电阻率ρs异常较为明显。分析了此次异常与内乡ML4.7级地震的关系，认为此次异常很有可能是内乡ML4.7级地震的短临前兆异常。当观测台站与震源位于同一构造带时，即便离震中较远，地电阻率对地震异常反映仍较灵敏，且与构造带同一走向的测向尤为明显。     

2-D viscoelastic FEM simulation on stress state in the deep part of a subducted slab

Introduction It is found that there are some relationships between the thermal structures of subduction zones and the deep seismicity, while the mechanism relates the thermal structure and the deep seismicity is still unsure (Helffrich, Brodholt, 1991; Furukawa, 1994; Kirby, et al, 1996). From 1980s, geoscientists have constituted a series of numerical simulations on the stress states of subduction slabs. Based on the kinetic computation of Sung and Burns (1976a, b), Goto, et al (1983, 1987…     

Simulation of artificial random field considering the temporal-spatial variation

Introduction For the seismic design of special structures such as nuclear power station, marine platform, long-span bridge and dam, generally the time-history response analysis of the structure under seismic excitation is imperative, which was coded in most seismic design codes. The earthquake records suitable for the seismic situation and site condition are necessary to be used as the seismic input in the dynamic analysis of structures. As a result of the limited observational condition of st…     

A comparison of tectonic ambient shear stress value in China with that in western USA

Introduction The stress status of the earths crust is closely related to global structure, the direction of plate movement, the drive mechanism of plate, earthquake cause, etc. Therefore the researches of the stress status of the earths crust and the process of dynamic evolution are paid a great attention to by many people around the world (Zoback, Zoback, 1980; Zoback, et al, 1989; Zoback, 1989; Spence, 1997; Fuchs, 1997; Plenefish, Bonjer, 1997; Muller, et al, 1997; XU, et al, 1989; WAN…     

Evapotranspiration from citrus trees growing in sandy soilunder drip irrigation with saline water

An experiment on evapotranspiration from citrus trees under irrigation with saline waterwas carried out for 4 months. Two lysimeters planted with a citrus tree in the green house wereused. One lysimeter was irrigated with saline water (NaCl and CaCl2 of 2000 mg/L equivalence,EC = 3.8 dS/m, SAR = 5.9) and the other was irrigated with freshwater using drip irrigation. Theapplied irrigation water was 1.2 times that of the evapotranspiration on the previous day.Evapotranspiration was calculated as the change in lysimeter weight recorded every 30 minutes.The lysimeters were filled with soil with 95.8% sand. The results of the experiment were as follows.(i) The evapotranspiration from citrus tree was reduced after irrigation with saline water. Theevapotranspiration returns to normal after leaching. However it takes months to exhaust the saltfrom the tree. ( ii ) To estimate the impact of irrigation with saline water on the evapotranspirationfrom citrus trees, the reduction coefficient due to salt stress (Ks) was used in this experiment.Evapotranspiration under irrigation with saline water (ETs) can be calculated from evapotranspira-tion under irrigation with freshwater (ET) by the equation ETs = Ks× ET. Ks can be expressed as afunction of ECsw. (iii) The critical soil-water electrical conductivity (ECsw) is 9.5 dS/m, beyondwhich adverse effects on evapotranspiration begin to appear. If ECsw can be controlled at below9.5 dS/m, saline water can be safely used for irrigation.     

多种驱动力作用下东亚大陆形变及应力场演化

将印度板块持续地向北推进、下伏地幔小尺度对流对增厚大陆岩石层的搬离作用以及剥蚀作用视为形成现今东亚大陆形变和应力场格局的主驱动力。在一梯形区域内，利用数值模拟的方法，研究了东亚大陆在不同的边界条件、不同的剥蚀率系数及不同的岩石力学参数条件下的形变及应力场格局。与现代空间大地测量技术 CGPS)以及利用地震观测得到的结果进行了对比。结果表明，本文模型预测的结果与上述的观测结果有较好的吻合，其西部地区比东部吻合得更好。说明控制东亚大陆西部形变和应力场基本格局的主驱动力，来源于印度板块对欧亚板块的碰撞、挤压，而对东部地区还应当考虑其与太平洋板块和菲律宾板块的相互作用。与此同时，下伏地幔小尺度对流对增厚大陆岩石层的搬离作用以及风化剥蚀对应力场的演化过程也不可忽视。