中国大陆及邻区地震活动背景、环境触发与地震预测研究

This dissertation that includes most of the P. PH.D research work during 2001~2002 covers the large-scale distribution of continental earthquakes in mainland China, the mechanism and statistic features of grouped strong earthquakes related to the tidal triggering, some results in earthquake prediction with correlativity analysis methods, and the flushes from the two strong continental earthquakes in South Asia in 2001. Mainland China is the only continental sub-plate that is compressed by collision boundaries at its two sides, within which earthquakes are dispersive and distributed as seismic belts with different widths. The control capability of the continental block boundaries on the strong earthquakes and seismic hazards is calculated and analyzed in this dissertation. By mapping the distribution of the 31282 ML:3s2,0 earthquakes, I found that the depth of continental earthquakes depend on the tectonic zonings. The events on the boundaries of relatively integrated blocks are deep and those on the new-developed ruptures are shallow. The average depth of earthquakes in the West of China is about 5km deeper than that in the east. The western and southwestern brim of Tarim Basin generated the deepest earthquakes in mainland China. The statistic results from correlation between the grouped M7 earthquakes and the tidal stress show that the strong events were modulated by tidal stress in active periods. Taking Taiwan area as an example, the dependence of moderate events on the moon phase angles (￡>) is analyzed, which shows that the number of the earthquakes in Taiwan when D is 50° ,50° +90° and 50° +180° is more than 2 times of standard deviation over the average frequency at each degree, corresponding to the 4th, 12th and 19th solar day after the new moon. The probability of earthquake attack to the densely populated Taiwan island on the 4th solar day is about 4 times of that on other solar days. On the practice of earthquake prediction, I calculated and analyzed the temporal correlation of the earthquakes in Xinjinag area, Qinghai-Tibet area, west Yunnan area, North China area and those in their adjacent areas, and predicted at the end of 2000 that it would be a special time interval from 2001 to 2003, within which moderate to strong earthquakes would be more active in the west of China. What happened in 2001 partly validated the prediction. Within 10 months, there were 2 great continental earthquakes in south Asia, i.e., the M7.8 event in India on Jan 26 and M8.1 event in China on Nov. 14, 2001, which are the largest earthquake in the past 50 years both for India and China. No records for two great earthquakes in Asia within so short time interval. We should speculate the following aspects from the two incidences: The influence of the fallacious deployment of seismic stations on the fine location and focal mechanism determination of strong earthquakes must be affronted. It is very important to introduce comparative seismology research to seismic hazard analysis and earthquake prediction research. The improvement or changes in real-time prediction of strong earthquakes with precursors is urged. Methods need to be refreshed to protect environment and historical relics in earthquake-prone areas.

塔里木盆地历史时期的自然环境演变

Exploit Tarim Basin Historical Physical Geographic Information System by linking historical documents and Geographic Information System, reconstruct the physical environmental evolution in Tarirn Basin during historical period (the last 2 Ka), special discuss riverhead of the Yellow River and Lop Nur. Based on analyzing Chinese historical documents (antiquity maps and texts), extract physical environmental information in Xiyu during historical period from Twenty-Five History and geographic books and records past dynasties, divide it into 4 period of time. Regarding digital topographical maps as base maps and looking on water bodies, vegetation and desert as central factors, quantify historical physical geographic data in Geographic Information System in terms of dynastic combination of Xianqin-Han, Jin-Wei-Nanbeichao, Tang-Wudai and Song-Yuan-Ming-Qing, execute physical environmental maps of Xiyu through the ages, in order to image the changes of water system, oasis and desert in Xiyu during the last 2 Ka. Compare cross orientation the relation of environmental factors all historical period of time from the influence of climate to oasis and desert, deem that climate condition decided ecological structure in direct and restrict the extent of desertification, especially climate corresponded the style of oasis and the spread of desert in the period of Jin-Wei-Nanbeichao and Tang-Wudai. Compare portrait direction the physical environmental characters in Xiyu during different period of time from 5 aspects of water bodies, oasis, desert, products and climate, deem that physical environment in Xiyu changed in all aspects during historical period. The origin of Lysenkoism about the Yellow River Undercurrent is agelong, whose ascending and descending at times due to investigating the riverhead of the Yellow River time after time during historical period and researching and disputing about the geographic location of Jishishan Mountain. It could consider the faultage in northeastern Qinghai-Xizang Plateau as the channels of undercurrent according to the research of modern geoscience field in the riverhead region.

宁夏固原寺口子剖面磁性地层与孢粉植物群初步研究

In Asia continent, several significant environmental events happened during the Cenozoic era, such as uplift of the Tibet Plateau, formation of the Asian Monsoon system, aridification of the temperate inland region in Central Asia. To investigate the history of long-term palaeoclimate evolution during the late Cenozoic, a lacustrine sequence located at Sikouzi, Guyuan county, Ningxia-Hui Autonomous Region, was studied. The Sikouzi section is about 2880 m in thickness and has a general continuous nature according to field observation. Thus this thick lacustrine record is an important archive to further understand those environmental events. In this study, detailed field measurement, layer-after-layer description and sampling, and magnetostratigraphy and palynoflora investigations are conducted at the Sikouzi section and some preliminary results have been achieved as follows. Based on Hipparion fauna, pollen data and long distinctive patterns of the local magnetozones, the confident correlation of the Sikouzi magnetostratigraphic polarity to the GPTS (CK95) is best established, indicating that the top boundary of the Sikouzi formation is dated back to -19.8 Ma B.P. and consequently no Oligocene sediments deposited locally. On the other hand, both the field observation and the correlation to GPTS indicate a nearly continuous nature for the whole sequence. The palynological results show that the grassland has been a dominant vegetation in the Sikouzi area since ~19.8 Ma B.P, although some trees/shrubs were present sparsely during the intervals of relatively warm and wet climatic conditions. This implies that the onset of the aridification in northwestern China is dated back to at least 19.8 Ma B.P. ago. The Neogene Global Climatic Optimum (-16.0 Ma B.P.) occurring between the late Early Miocene and the early Middle Miocene is well documented in the Shanwang formation, Shandong Province. However, such event was not found in the Sikouzi record, and neither in the Guide and the Hualong basins, Qinghai province. This may lead us to the conclusion that the East-Asian Summer Monsoon system remained weak during the period of the Miocene Climatic Optimum although the onset of it was traced back to the Early Oligocene. In the Sikouzi area, it was warm between the latest Miocene and the early Pliocene and then became cool in the late Pliocene. This pattern is consistent with the palaeoclimate record of the Pliocene from other areas in the world.

中国特有针叶树种对气候变化的敏感性研究

About 214 trees in 9 sampling sites, representing 5 endemic conifer species, were collected from the western Sichuan Province and eastern Qinghai Province, China. In this study, structure we try to investigate tree-ring sensitivity to climate in order to obtain primary information of reconstructing past climate from the trees in this region. All the 5 species present distinct ring boundaries ^ few ABS(absent rings) and available for cross-dating,which are all past the test by program COFECHA. Statistics for all the 8 tree-ring width residual chronologies present significant inter-correlation between series and high values of mean sensitivity. As well as the maximum latewood density of Picea crassifolia Kom and Pinus densata Mast. These results indicate usefulness of these chronologies for dendrochronological studies. Pearson correlation analyses were applied to provide a basic estimate of the causal relationships between tree-ring width and climate factors. We found some significant relationships between tree-ring width> maximum density and temperature as well as precipitation. Especially, there is high correlation between the maximum density of the Picea crassifolia Kom and the index of moisture, the ratio of precipitation and temperature, which can indicate well the climate; however the higher correlation can be see between the maximum density of Pinus densata Mast and the total temperature from June to September. Regardless of tree species, chronologies in our study region presented accordant variations of which may reveal strong common climate signal. Thus these chronologies are shown to be dependable for building tree-ring network in the nearly future. However, there are limitations in this study, only monthly mean of temperature and precipitation were available. Also, for this typical subtropical mountain system, meteorological stations are usually located in valley and biased to represent moisture conditions on the slopes. Thus the estimation of precipitation both in temporal and spatial domain was rather restricted. Further study, such as wood anatomy, physiology and densitometry, are needed for better understanding the environmental and climatic history in this area.

地幔对流理论及其在解释地球物理观测的应用

With the improving of mantle convection theory, the developing of computing method and increasing of the measurement data, we can numerically simulate more clearly about the effects on some geophysical observed phenomenons such as the global heat flow and global lithospheric stress field in the Earth's surface caused by mantle convection, which is the primary mechanism for the transport of heat from the Earth's deep interior to its surface and the underlying force mechanism of dynamics in the Earth.Chapter 1 reviews the historical background and present research state of mantle convection theory.In Chapter 2, the basic conception of thermal convection and the basic theory about mantle flow.The effects on generation and distribution of global lithospheric stres s field induced by mantle flow are the subject of Chapter 3. Mantle convection causes normal stress and tangential stresses at the bottom of the lithosphere, and then the sublithospheric stress field induces the lithospheric deformation as sixrface force and results in the stress field within the lithosphere. The simulation shows that the agreement between predictions and observations is good in most regions. Most of subduction zones and continental collisions are under compressive. While ocean ridges, such as the east Pacific ridge, the Atlantic ridge and the east African rift valley, are under tensile. And most of the hotspots preferentially occur in regions where calculated stress is tensile. The calculated directions of the most compressive principal horizontal stress are largely in accord with that of the observation except for some regions such as the NW-Pacifie subduction zone and Qinghai-Tibet Plateau, in which the directions of the most compressive principal horizontal stress are different. It shows that the mantel flow plays an important role in causing or affecting the large-scale stress field within the lithosphere.The global heat flow simulation based on a kinematic model of mantle convection is given in Chapter 4. Mantle convection velocities are calculated based on the internal loading theory at first, the velocity field is used as the input to solve the thermal problem. Results show that calculated depth derivatives of the near surface temperature are closely correlated to the observed surface heat flow pattern. Higher heat flow values around midocean ridge systems can be reproduced very well. The predicted average temperature as a function of function of depth reveals that there are two thermal boundary layers, one is close to the surface and another is close to the core-mantle boundary, the rest of the mantle is nearly isothermal. Although, in most of the mantle, advection dominates the heat transfer, the conductive heat transfer is still locally important in the boundary layers and plays an important role for the surface heat flow pattern. The existence of surface plates is responsible for the long wavelength surface heat flow pattern.In Chapter 5, the effects on present-day crustal movement in the China Mainland resulted from the mantle convection are introduced. Using a dynamic method, we present a quantitative model for the present-day crustal movement in China. We consider not only the effect of the India-Eurasia collision, the gravitational potential energy difference of the Tibet Plateau, but also the contribution of the shear traction on the bottom of the lithosphere induced by the global mantle convection. The comparison between our results and the velocity field obtained from the GPS observation shows that our model satisfactorily reproduces the general picture of crustal deformation in China. Numerical modeling results reveal that the stress field on the base of the lithosphere induced by the mantle flow is probably a considerable factor that causes the movement and deformation of the lithosphere in continental China with its eflfcet focuing on the Eastern China A numerical research on the small-scale convection with variable viscosity in the upper mantle is introduced in Chapter 6. Based on a two-dimensional model, small-scale convection in the mantle-lithosphere system with variable viscosity is researched by using of finite element method. Variation of viscosity in exponential form with temperature is considered in this paper The results show that if viscosity is strongly temperature-dependent, the upper part of the system does not take a share in the convection and a stagnant lid, which is identified as lithosphere, is formed on the top of system because of low temperature and high viscosity. The calculated surface heat flow, topography and gravity anomaly are associated well with the convection pattern, namely, the regions with high heat flow and uplift correspond to the upwelling flow, and vice versa.In Chapter 7, we give a brief of future research subject: The inversion of lateral density heterogeneity in the mantle by minimizing the viscous dissipation.