“板块”模型的能量问题探析

本文论述"板块"模型中的能量问题,从实例出发,细化分析解题思路,有效找到解决问题的突破口,帮助学生更好地掌握解决问题的方法。

“板块-金字塔式”模型设计及其对地质构造类课程教学的靶向意义

学生的知识面各不相同,掌握深度也千差万别,给教学带来了困难。对于地质构造类课程,尝试在教学过程中设计实施一种“板块-金字塔式”教学模型,再结合对学生学习状况的精准管理,以期达到更好的教学效果。本文以构造地质学教学为例,将整个课程分割成四个板块,再将各个板块按不同深度层次以“金字塔式”加以开发,从而满足不同基础的同学学习需要。不断完善“板块-金字塔式”教学模型,对于开展精准教学活动和提高教学效果十分有利。模型具有可塑性,可随科技发展而更新。

Initiation and evolution of the South China Sea: an overview

Different models have been proposed for the formation and tectonic evolution of the South China Sea （SCS）, including extrusion of the Indochina Peninsula, backarc extension, two-stage opening, proto-SCS dragging, extension induced by a mantle plume, and integrated models that combine diverse factors. Among these, the extrusion model has gained the most attention. Based on simplified physical experiments, this model proposes that collision between the Indian and Eurasian Plates resulted in extrusion of the Indochina Peninsula, which in turn led to opening of the SCS. The extrusion of the Indochina Peninsula, however, should have led to preferential open- ing in the west side of the SCS, which is contrary to observations. Extensional models propose that the SCS was a backarc basin, rifted off the South China Block. Most of the backarc extension models, however, are not compatible with observations in terms of either age or subduction direction. The two-stage extension model is based on extensional basins surrounding the SCS. Recent dating results indeed show two-stage opening in the SCS, but the Southwest Subbasin of the SCS is much younger, which contradicts the two-stage extension model. Here we pro- pose a refined backarc extension model. There was a wide Neotethys Ocean between the Australian and Eurasian Plates before the Indian-Eurasian collision. The ocean floorstarted to subduct northward at ~ 125 Ma, causing backarc extension along the southem margin of the Eurasian Plate and the formation of the proto-SCS. The Neotethys sub- duction regime changed due to ridge subduction in the Late Cretaceous, resulting in fold-belts, uplifting, erosion, and widespread unconformities. It may also have led to the subduction of the proto-SCS. Flat subduction of the ridge may have reached further north and resulted in another backarc extension that formed the SCS. The rollback of the fiat subducting slab might have occurred ~ 90 Ma ago; the second backarc extension may have initiated between 50 and 45 Ma. The opening of the Southwest Subbasin is roughly simultaneous with a ridge jump in the East Sub- basin, which implies major tectonic changes in the sur- rounding regions, likely related to major changes in the extrusion of the Indochina Peninsula.

Stability analysis for main roof of roadway driving along next goaf

Focusing on the stability of surrounding rock around the roadway driving along next goaf with a narrow coal pillar, a mechanics model of the triangle block structure of main roof above the roadway is established, and the sliding stability coefficient K 1 and the rotation stability coefficient K 2 are proposed to describe the stability of the triangle block structure quantitatively. The structure can keep a self stability before and after the roadway excavation, at the stage of mining induced effect, the stability of the structure is lowered, and the structure may become instability with decreasing the coal strength, increasing the mining height of working face and the mining depth.

Global Plate Motions and Their Impact on the Earth's Surface Area Change

Based on their Euler poles, we calculated the relative velocities between every two plates in the typical global plate motion models, respectively, and estimated the area change along these boundaries. In our calculations, plates on both sides accommodated area changes depending on the boundary types： extensional, convergent or transform, so we can estimate area change of each plate and then globally. Our preliminary results show that the area of the southern hemisphere increased while that of the northern hemisphere decreased over the past I million years, and global area has increased by 26,000km^2 to 36,000km^2, which corresponds to the 160m - 250m increment on the Earth＇s radius if all these area increments are attributed to Earth＇s expansion. Taking the NUVEL-1 model as an example, of the 14 plates in this model, 11 are decreasing, but the global area has increased because of the larger increment amount from Africa, North America and Antarctica. Finally, we also discussed factors affecting the global area change such as subduction zone retreating and back-arc spreading.

A MAXIMUM ENTROPY CHUNKING MODEL WITH N-FOLD TEMPLATE CORRECTION

This letter presents a new chunking method based on Maximum Entropy (ME) model with N-fold template correction model.First two types of machine learning models are described.Based on the analysis of the two models,then the chunking model which combines the profits of conditional probability model and rule based model is proposed.The selection of features and rule templates in the chunking model is discussed.Experimental results for the CoNLL-2000 corpus show that this approach achieves impressive accuracy in terms of the F-score:92.93%.Compared with the ME model and ME Markov model,the new chunking model achieves better performance.

Fault Type Analysis along the San Andreas Fault Zone: A Numerical Approach

Finite Element (FE) modeling under plane stress condition is used to analyze the fault type variation with depth along and around the San Andreas Fault (SAF) zone. In this simulation elastic rheology was used and was thought justifiable as the variation in depth from 0.5 km to 20 km was considered. Series of calculations were performed with the variation in domain properties. Three types of models were created based on simple geological map of California, namely, 1) single domain model considering whole California as one homogeneous domain, 2) three domains model including the North American plate, Pacific plate, and SAF zone as separate domains, and 3) Four domains model including the three above plus the Garlock Fault zone. Mohr-Coulomb failure criterion and Byerlee's law were used for the calculation of failure state. All the models were driven by displacement boundary condition imposing the fixed North American plate and Pacific plate motion along N34°W vector up to the northern terminus of SAF and N50°E vector motion for the subducting the Gorda and Juan de Fuca plates. Our simulated results revealed that as the depth increased, the fault types were generally normal, and at shallow depth greater strike slip and some thrust faults were formed. It is concluded that SAF may be terminated as normal fault at depth although the surface expression is clearly strike slip.

Basic Characteristics of Active Structures in Western Sichuan and Its Vicinity and Strong Earthquake Recurrence Model

Western Sichuan and its vicinity are located in the juncture of three big active blocks, namely, the Chuandian （Sichuan and Yunnan）, the Bayan Har and the South China blocks, on the eastern margin of the Qinghai-Xizang（Tibet） Plateau. Many groups of active faults that are capable of generating earthquakes are developed there. Because there exist lateral secondary active faults, the Chuandian block can be further divided into the central Yumlan and northwestern Sichuan sub-blocks; while the Longmenshan sub-block can be divided on the east end of the Bayan Har block. Joint exploration of deep crustal structure shows that there exist low-velocity and high-conductivity layers in the crust of the Chuandian and Bayan Har blocks, which are one of the important factors that make the upper crust prone to earthquake. The results of geological study and modern GPS observation show that blocks of different orders all have SE- or SSE-trending sliding, clockwise rotation and upwelling movement; but there are some differences in amplitude. This paper has also given the geological or GPS slip rates of main active fault zones and discussed the main scientific problems still existing now.

A New Model of Lithosphere Deformation Beneath the Okinawa Trough Based on Gravity Data

The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal subduction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deformation at the collision front, while the oblique subduction in the southern part gives rise to a smaller accretion with small deformation than that in the northern part. The mechanisms that cause the distinction between these two types have been analysed and calculated by using gravity data based on the lithosphere rheology and the stress state of the lithosphere in the subduction boundary. The two types of subduction model are associated with the internal extension in the southern Okinawa Trough and the small extension in the northern part. The difference of the stress state between the two types of subduction model is also manifested in other tectonic features, such as topography, volcanic activity and crust movement. Modeling bathymetric and gravity data from this area suggests that the oblique subduction of low angle, together with smooth geometry of the overlying plate crust, results in small stress released on the south of the trench by the subduction plate. The intraplate faults in the southern Okinawa Trough behind the trench stand in surplus intensive stress. On the other hand, the normal subduction of high angle, together with strong undulation geometry of the overlying crust, results in more intensive stress released in the northern Ryukyu Trench than that in the south. The intraplate faults in the northern Okinawa Trough behind the northern Ryukyu Trench stand in small stress.

A dislocation-based model for cyclic plastic response of lath martensitic steels

Softening behavior of lath martensitic steels is related to the coarsening of laths and dislocation evolution during cyclic deformation.Involving the physical mechanism,we developed a dislocation-based model to study the cyclic plastic response for lath martensitic steels.For a block,we proposed an interfacial dislocation evolution model to physically present the interaction between mobile dislocations in the block and interfacial dislocations by considering the coarsening mechanism of the laths.Moreover,the evolution behavior of backstress caused by dislocation pile up at the block boundary has been considered.Then,a hierarchical model based on the elastic-viscoplastic self-consistent(EVPSC)theory is developed,which can realize the scale transition among representative volume element(RVE),prior austenite grains(PAGs)and blocks.According to the proposed model,the effective mechanical responses including the cyclic hysteretic loop and peak stress at different cycles for lath martensitic steel have been theoretically predicted and investigated.