交通变革视阈下郑州地域构造的演化

郑州的地域交通从以传统水运和驿道为主到以近代铁路为主导,经历了由盛及衰、复又兴起的演化过程。平汉、陇海铁路的筑通,改变了中原地区的交通布局,突破了郑州地域发展的时空限制,为区域社会变迁带来了前所未有的变革力量。郑州交通区位的提升,使得传统的运输渠道以及区域间人员商货的基本流向由此发生转换,郑州地域的经济体系和空间结构亦随之发生变化。以铁路为代表的现代交通体系,促进了区域经济中心由水运便利之地向铁路沿线城市的位移,郑州逐步发展成为地域经济的中心地;郑州以铁路为桥梁连通外部世界,改变了该地域传统、落后的状况,促进了区域经济的市场化、外向化转型,从而引发区域商业和工业空间的演变;由于铁路交通网络的形成,使得原本分散的地域结构和人口布局呈现聚集的趋势,由此带来郑州区域市镇的兴衰更替,传统市镇趋于衰落,铁路沿线一批新兴市镇悄然崛起。

人口问题归根结蒂是发展问题——访日本厚生省人口问题研究所地域构造研究室室长若林敬子

记者:中国的计划生育政策在国际上引起的争议最大,而且被美国等西方国家列为中国人权状况不佳的典型事例,您作为一名外国学者,又是怎样看待这个问题的呢? 若林:中国是世界上头号人口超大国,中国的人口问题不仅仅是中国自身的问题,而是世界人口问题中的一个问题。从这个观点出发,中国能有效地抑制人口增长,是对世界的贡献,是理应给予肯定的。至于“人权”,我认为人权观是多元的。

Relocation of Earthquakes in the Northeastern Tianshan Mountains Area and Improvement of Local 1-D Crustal Velocity Model

We apply three methods to relocate 599 earthquake events that occurred from August 2004 to August 2005 in the northeastern Tianshan Mountains area ( 85°30' ～ 88°30'E,43°00' ～ 44°40' N ) by using travel times recorded by regional seismic network and 10 portable seismic stations deployed around the Urumqi city. By comparing the reliability of different results,we determined a suitable location method,and an improved 1-D crustal velocity model of the study area. The uncertainty of earthquake location is significantly reduced with combined data of seismic network and portable stations. The relocated events are clearly associated with regional tectonics of the northeastern Tianshan Mountains area, and are also in agreement with the existence of active faults imaged by deep seismic reflection profile. The relocated seismicity discovers some potential traces of buried active faults,which need to be validated further.

Research on the Seismotectonic Setting in Beibu Gulf Waters

In this paper we discuss the seismogenic structures of the two earthquakes occurring in the Beibu Gulf waters,based on the investigation of geological structure,faults,geophysical fields,seismicity and earthquake focal mechanism.The results show that the NEE trending faults along the boundary of the Wushi depression are the dominating seismogenic structures,and the NW trending faults are the key factors of stress concentration.The results also show that high seismicity has a significant relationship with the late Cenozoic deposition center in the Beibu Gulf,and their NE-NEE trending boundary faults are important to the identification of seismogenic structures.The special arcuate fault segment or the intersection point of the NW trending faults and NE-NEE trending boundary faults is a possible location of future earthquakes.

Modern movement and deformation in the South China Sea shown by GPS measurements and numerical simulation

To better understand the crustal deformation of the South China Sea Basin, we produce a mechanically consistent 2-dimensional model for observing regional velocity field in the South China Sea (SCS). We studied the dominating regional tectonic stress field by geodetic measurements and finite element analysis, the spatial variations of velocity field and strain field, and relative movements among different blocks, using a 2-dimensional model describing crustal deformation of the South China Sea Basin. Strain results show that the SCS is extending at present. The western part of SCS is opening gradually in NW- SE direction from its northern margin to the south, but the eastern part of SCS is opening gradually from its central part to the north and south. In addition, we analyzed the plate kinematics to the deformation of the SCS, using a two-dimensional finite element model. Our simulations results are well explained by available geodetic data. The movement of SCS is resulted from interactions among Indian Plate, Pacific Plate, Philippine Sea Plate, and Eurasian Plate.

The Relationship Between Strong Earthquake Activity of M_S≥7.0 on the Chinese Mainland and the West Kunlun-A'nyêmaqên Secondary Arcuate Tectonic Zone

The active and quiet phenomenon of moderate strong earthquakes one year before the earthquakes with M S≥7.0, the spatial distribution characteristics of the solid tide modulating and triggering earthquakes and the strong earthquake mechanisms on the Chinese continent have been studied. The secondary arcuate tectonic zone composed of the west Kunlun-Anyêmaqên faults is believed to be a very important boundary to characterize strong earthquake activity of M S≥7.0 on the Chinese continent, that is, a boundary between the seismically active region and the quiet region of moderately strong earthquakes one year before earthquakes with M S≥7.0, and a boundary of the spatial distributions between the solid tide modulating strong earthquakes (M S≥7.0) and the non-modulating ones. It might be related with the characteristics of spatial distribution of focal mechanism solutions of strong earthquakes on the Chinese Continent.

Tectonic Background of the Yutian M_S7.3 Earthquake in 2014 and Its Relationship with the Yutian M_S7.3 Earthquake in 2008

The regional tectonic background and characteristics of active faults of the Yutian MS7.3earthquake on February 12,2014 are discussed in this paper.After the analysis of the epicenter area of the MS7.3 earthquake in 2014 and the focal mechanisms of the former strong earthquakes around it,the authors deduced that the seismogenic fault of the MS7.3earthquake is the east branch of the Ashikule fault.The MS7.3 earthquake in 2014 and the MS7.3 earthquake in 2008 are two strong earthquake events on the different sections of the Altun Tagh fault,where the fault behavior changes from sinistral slip to normal faulting because of the extensional tail effects in the southern end of the Altun Tagh fault.It is concluded that the two MS7.3 earthquakes have the same dynamic source,and the MS7.3earthquake in 2008 promoted the occurrence of the MS7.3 earthquake in 2014.Finally,we calculate the Coulomb stress change to the seismogenic fault of the MS7.3 earthquake in2014 from the MS7.3 earthquake in 2008 using the layered crust model.The result also shows that the MS7.3 earthquake in 2008 accelerated the occurrence of the MS7.3earthquake in 2014.

The Focal Mechanism Solutions of the M_S 8.0 Wenchuan Earthquake in Sichuan on May 12,2008 and Some of Its Aftershocks

The focal mechanism solutions of the Wenchuan earthquake （Ms8.0） of May 12, 2008 and some of its aftershocks occurring up to December I0, 2008 are determined with lower semisphere of equal-projection and first motion sign data of P waves from regional and distant stations. The focal mechanism solutions of the Ms8.0 Wenchuan earthquake are： Nodal plane I：strike 5°, dip angle 48°, slip angle 39°; Nodal plane II： strike 247°, dip angle 62°, slip angle 131°; P axis azimuth 309°, plunge 8°, T axis azimuth 208°, plunge 54°, B axis azimuth 44°, plunge 35% Combining geological tectonics and spatial distribution of aftershocks, nodal plane II can be identified as a seismogenic fault. According to focal mechanism solutions, the fault activity that triggered the huge earthquake is reverse thrusting. The main rupture surface is S67°W, basically identical to the fault strike on which the earthquake occurred. The main compression stress P axis is N51°W, which is basically the same as the direction of the regional tectonic stress field. According to the results of focal mechanism solutions of aftershocks, the aftershocks occurring in the southern and northern sections of the Longmenshan fault zone have predominant orientations and are obviously different. For the main shock and the early aftershocks occurring on the southern section of the Longmenshan fault, the rupturing is mainly characterized by reverse-dip slip with some strike-slip, and over time, the aftershocks migrated towards the northern section. The rupturing in the source is mainly characterized by strike-slip with some reverse-dip slips. The stress field is controlled by the main shock stress field in the southern section of the Longmenshan tectonic zone, while it is controlled by the main shock stress field and regional stress field in the northern section of the Longmenshan tectonic zone.

FORMATION AND EVOLUTION OF THE CENOZOIC THRUST FOLD BELT IN JINPING, SICHUAN

The Jinping orogenic belt in Sichuan, China consists mainly of the Jinpingshan intracontinental thrust-nappe belt, foreland thrust-nappe belt and foreland uplift belt. Based on analyses about the characteristics of the structural units in this area, the authors propose in this paper that Chapuzi-Bazhe revival fault belt is the regional boundary fault, and points out that after the formation of the Pre-Sinian basement, the western edge of the Yangtze paraplatform was turned into the passive continental margin in Sinian to Triassic, then into the Mesozoic collision orogenic belt, and finally into the Cenozoic orogenic belt through intracontinental orogeny.

Analysis on the Focal Mechanism and Seismogenic Structures of the Yao’an earthquake with M_S6. 0,20091

Using the joint inversion method with the amplitude ratio of P-wave,SV-wave and SHwaves,this paper calculates the focal mechanisms of the aftershock sequence of the Yaoan earthquake with MS6. 0. According to the spatial distribution of earthquake sequence,the author analyzes the characteristics of the stress field and seismogenic fault. The result shows that:( 1) the seismogenic fault of the Yaoan earthquake is a vertical right-lateral strike-slip fault,striking NWW-SEE. The result is reliable and consistent with the nodal planes of the Harvard CMT solution and also in accord with the predominant direction of aftershocks.( 2) The predominant direction of principal compressive stress,NWW-SEE is consistent with the regional tectonic stress,and some aftershocks are different from the main shock. The stress field of the main shock is controlled by the regional tectonic stress field,indicating the diversity and complexity in the seismic area.( 3) By comprehensively analyzing the distribution of the earthquake sequence,focal mechanism and fault structure in the seismic area,it is found that the Maweijing fault is the seismogenic fault of the Yaoan earthquake.

A Brief Introduction to the Seismotectonic Map of Xinjiang and Its Neighborhood

This paper briefly introduces the Seismotectonic Map of Xinjiang and its neighborhood in the scale of 1∶2500000.The map is amended,supplemented and expanded based of the newly compiled Seismotectonic Map of Xinjiang in scale 1∶1000000.The base map of this seismotectonic map is the geologic map of western China and its neighborhood compiled by Li Tingdong.The abundant new materials from related research,referential literatures and the analyses on remote sensing data were used in the compiling work.A database and relevant documents are built for nearly 300 active faults and 150 active folds.The basic information of the major active faults,especially those near the border areas in this map are introduced in this paper.

Comparative Study of Changes in Stress-drop of the Jinggu MS6.6 and Ludian MS6.5 Earthquake Sequences

The earthquake stress-drop values of two sequences were accurately calculated after taking away the effects due to regional earthquake anelastic attenuation and station site response,using waveform data and seismic phase data of sequences of the Jinggu M_S6. 6,and Ludian M_S6. 5 earthquakes in Yunnan. These results show that the stress drop with magnitude increases within the scope of this study of magnitude. After eliminating the influence of the magnitude,the average value of stress-drop in the Jinggu sequence is higher than that of the Ludian sequence at the same magnitude range. This may be related to the stress state in different regions. In terms of the changes of time and space of stress-drop,before M_S5. 8 strong aftershock,the stress-drop is "slowing down-turning up-keeping a high value"after the mainshock,meanwhile,almost all of the abnormally high stress drop value is distributed around the M_S5. 8 strong aftershock, showing that the stress environment in the region was increasing after the mainshock. And after the M_S5. 9 strong aftershock,stress-drop rapidly declines to a relatively stable state,meanwhile,the high value of stress-drop is distributed around the strong aftershock,showing that the regional tectonic stress gets more fully release,its stress environment begins to rapidly decrease.For the Ludian sequence without a strong aftershock occurring,the average value of stress drop is lower than that of the Jinggu earthquake sequence at the same magnitude range,while at the same time,the stress-drop of the aftershock sequence almost hasn't changed much. In the time after the mainshock,combined with the release characteristics of the main energy,the stress in the region is excessively released,the subsequent stress in the region gradually returns to normal. This may be the reason why the activity of Ludianaftershocks significantly was weaker and subsequently there were no strong aftershocks occurred.

Comprehensive Research on Focal Mechanism Solutions in the Capital Circle Area of China

Comprehensive statistical analysis was performed on the basic features of focal mechanisms of 619 ML≥2. 0 earthquakes which occurred in the capital circle area from January 2002 to June 2010. By dividing the capital area into three studying regions based on regional tectonic characteristics,cluster analysis was conducted on the focal mechanisms of all subregions using the longest distance method in the statistical cluster analysis to study the characteristics of tectonic stress tensors. The result shows that dominant P-axis azimuth distribution is NNE-NEE and that of T-axis is NNW-NWW,most of the focal areas are controlled by a horizontal stress field and rupture is mainly of horizontal strike-slip. The maximum principal compression stress orientation is NE75° in the west,NE62° in the middle,and near EW in the east of the capital area. The regional tectonic stress field is characterized by horizontal compression.

The research and demonstration of some major geological problems of Three Gorges Project

The research process,main contents,methods and conclusions for some major engineering geological problems of the Three Gorges Project (TGP) are reviewed and introduced,including dam site selection,regional tectonic stability and seismic activity,stability of reservoir bank and reservoir-induced earthquake.Meanwhile,the above mentioned engineering geological problems are evaluated according to the preliminary test results since TGP operation and impoundment in 2003.

Crustal Deformation Derived from GPS in the Chinese Mainland from 1991-2004

Based on GPS data from 1991- 2004 and the least-squares collocation method,we analyze the crustal deformation in the Chinese mainland. The results show that the first-order crustal deformation is unchanged in different periods in the Chinese mainland,which reflects the background of regional tectonic activity. The strain rate is much higher in Western China,especially in the Qinghai-Tibetan Plateau and Sichuan-Yunnan area. The variations in different periods are related with seismicity of strong earthquakes during the same time. The GPS data after 2004 shows the post-seismic deformation of the 2001 Kunlun Mountains M S8. 1 earthquake.

The Quaternary Tectonic Stress Field of the Kunming Basin and Its Surrounding Areas

The Kunming basin is a Cenozoic faulted basin controlled by N-S trending active faults. there are totally 8 main active faults in and around the Kunming basin area. Inversion of fault slip data suggests that the stress field of the Kunming basin has experienced two major stages. In the first stage ( from the late-Pliocene to mid-Pleistocene),the regional tectonic stress field was characterized by near E-W compression and near N-S extension. In the second stage (from the late-Pleistocene to the present),the tectonic stress field has been mainly characterized by NNW-SSE compression and NEE-SWW extension. Under such a stress field,the near N-S trending faults in the region mainly show a lateral slip.

The provenance of Gansu Group in Longxi region and implications for tectonics and paleoclimate

The Neogene sediments of Gansu Group from northwestern China contain eolian and fluvial deposits.The origins of these sediments are very important for exploring the onset of Asian inland aridification,the pattern of paleo-atmospheric circulation,and the regional tectonics and geomorphic evolution during the Miocene.Here we present detrital-zircon age spectra of typical eolian and fluvial deposits from highlands and subsidence basin,and compare them with those of surrounding eroded mountain(such as the West Qinling Mountains and Liupan Mountains)materials and Quaternary loess derived from the Asian inlands.The results reveal that(1)the detrital-zircon age spectrum of the Miocene eolian sample is remarkably different from the eroded materials of the West Qinling Mountains and the Miocene fluvial deposits from Tianshui region,but very similar to the Quaternary loess deposits.This indicates that the provenance of Miocene eolian sediments is similar with the Quaternary loess,and thus further confirms the previous conclusions that the distribution of Asian arid lands and the pattern of atmospheric circulation during the Miocene are broadly similar with the Quaternary.(2)The detrital-zircon age spectrum of the fluvial deposits(with age about 11.5 Ma)from Tianshui region is different from the eroded materials of West Qinling Mountains,but similar with that of the Liupan Mountains to the east,which may suggest that the Liupan Mountains have already been exhumed by11.5 Ma.

Regional differences in crustal structure of the North China Craton from receiver functions

Moho depth and crustal average Poisson＇s ratio for 823 stations are obtained by H-n： stacking of receiver functions. These, to- gether with topography and receiver function amplitude information, were used to study the crustal structure beneath the North China Craton （NCC）. The results suggest that modified and preserved crust coexist beneath the craton with generally Airy-type isostatic equilibrium. The equilibrium is relatively low in the eastern NCC and some local areas in the central and western NCC, which correlates well with regional geology and tectonic features. Major differences in the crust were observed beneath the eastern, central, and western NCC, with average Moho depths of 33, 37, and 42 km and average Poisson＇s ratios of 0.268, 0.267 and 0.264, respectively. Abnormal Moho depths and Poisson＇s ratios are mainly present in the rift zones, the northern and southern edges of the central NCC, and tectonic boundaries. The crust beneath Ordos retains the characteristics of typical craton. Poisson＇s ratio increases roughly linearly as Moho depth decreases in all three parts of the NCC with different slopes. Receiver function amplitudes are relatively large in the northern edge of the eastern and central NCC, and small in and near the rifts. The Yanshan Mountains and southern part of the Shanxi rift show small-scale variations in the receiver-function ampli- tudes. These observations suggest that overall modification and thinning in the crust occurred in the eastern NCC, and local crustal modification occurred in the central and westem NCC. Different crustal structures in the eastern, central, and western NCC suggest different modification processes and mechanisms. The overall destruction of the crustal structure in the eastern NCC is probably due to the westward subduction of the Pacific Plate during the Meso-Cenozoic time; the local modifications of the crust in the central and western NCC may be due to repeated reactivations at zones with a heterogeneous structure by successive thermal-tectonic events during the long-term evolution of the NCC.

3-D geologic architecture of Xiong＇an New Area： Constraints from seismic reflection data

Studying the geologic architecture of the Xiong'an New Area will provide important basis for the evaluation of crustal stability, urban planning and infrastructural projects in this region, and it is also of great significance in exploring the occurrence of oil and gas, geothermal, hot dry rock and other resources. The stratigraphic system of the study area is established by using latest high quality seismic reflection and deep borehole data. Characteristics of the major faults developed in the study area are finely depicted with the method of structural analysis. Tectonic evolution of Xiong'an and adjacent areas is reconstructed by using balanced geological cross-section technique. The tectonic activity of the study area is discussed on the basis of the development of secondary faults and the distribution of active earthquakes across the region. This study demonstrates that Xiong'an New Area is located at the transfer zone of the central and northern Jizhong Depression. There are three regional unconformities developed in this area, by which four structural layers are sub-divided. Controlled by the Taihang Mountain piedmont fault, the Daxing fault, the Rongcheng fault and the Niudong fault, the structural framework of the study area is characterized by intervening highs with sags. This structural pattern has an important controlling over the reservoir characteristics, hydrocarbon accumulation and the distribution of geothermal resources and hot dry rock within this region. Rifting in this area began in the early Paleogene, exhibiting typical episodic character and became inactive in Neogene. The development feature of secondary faults along with the distribution of active earthquakes indicate that Xiong'an New Area has been in a relatively stable tectonic setting since the Neogene, while the Baxian Sag and other structural units to the east of it have obviously been in a rather active environment.

Characteristics of the crustal magnetic anomaly and regional tectonics in the Qinghai-Tibet Plateau and the adjacent areas

Study of the characteristics of the crustal magnetic anomaly in the Qinghai-Tibet Plateau and the adjacent areas helps better understand the lithospheric structure and evolution, as well as the regional geodynamic processes. Here we analyze the distri- bution laws of the crustal magnetic anomaly and its vertical gradient, the decay characteristics of the anomaly, the contribu- tions from different wavelength bands to the anomaly, and the relationship between the anomaly and the crustal regional tec- tonics in the plateau and nearby, based on a new and higher degree geomagnetic model NGDC-EMM-720-V3 constructed from the surface, aeromagnetic, marine and satellite survey data. The results reveal that the positive and negative anomalies in the Qinghai-Tibet Plateau are weak, while those of the surrounding areas are strong. The boundary agrees well with the border of the plateau regional tectonics. The anomaly is nearly east-west in the central and western plateau, arc-shaped in the south- western and eastern, and nearly north-south in the southeastern, consistent with the tectonic trends. There are strong negative anomaly loci in the east and west syntaxis, whereas no significant differences exist among the Cenozoic blocks in the plateau interior. No direct correspondence exists between the anomaly and the crustal depth. On the background of a weak magnetic anomaly in the plateau, relatively stronger short wavelength fields from the shallower crust are overlapped in the Lhasa, Qilian, Qaidam, and Sichuan-Yunnan rhombic blocks. A strong negative anomaly in the east-west direction is distributed along the Himalayas, mainly caused by the middle and long wavelength bands in the deep and central crust. The magnetic structural lay- ers are stable in the Sichuan and Tarim basins. The anomalies at different altitudes over the southern plateau vary strongly, showing a drastic variation in the magnetic structure from the deep crust to the shallow crust.