2009 Vol. 15, No. 2

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NUMERICAL MODELING FOR WENCHUAN EARTHQUAKE MECHANISM
WANG Lian-jie, CUI Jun-wen, ZHOU Chun-jing, SUN Dong-sheng, WANG Wei, TANG Zhe-min, QIAN Hua-shan
2009, 15(2): 105-113.
Abstract (132) HTML (64) PDF (850KB)(11)
Abstract:
In this paper, strain softening model is used for modeling the Wenchuan earthquake.Results shows that this earthquake was caused by compressing of Qinghai-Tibet Plateau and block of Sichuan Basin.The stress drop, energy release amount, the magnitude of dislocation of fault, coseismic displacement, displacement before earthquake and earthquake recurrence intervals are given by the modeling.The modeling results are in good agreement with geologic and geomorphologic survey and others data.
STABILITY AND STRESS MEASUREMENT NEAR THE QINGCHUAN FAULT IN THE NORTHERN LONGMEN MOUNTAINS
PENG Hua, MA Xiu-min, JIANG Jing-jie
2009, 15(2): 114-130.
Abstract (154) HTML (76) PDF (3932KB)(16)
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After the M8.0 Wenchuan earthquake, it becomes an important concern that whether aftershocks direct to Hanzhong along the Qingchuan fault and a strong aftershock also occur.The study on in situ stress measurements was carried out at Ningqiang region in the northeastern section of the fault in order to master the changes of the coulomb stress in the Qingchuan fault after the earthquake and to identify the development trend of aftershocks, using the hydraulic fracturing in situ stress measurement techniques on June 2 to 28, 2008.The size, orientation and distribution of the tectonic stress in the fault were obtained respectively by the hydraulic fracturing and stress relieving in three boreholes.According to the measured stress data, the direction of the maximum level principal stress is NE-NEE near the fault, and does not accord with the SN-NNE direction of the regional tectonic stress.It is shown that the stress state near the fault changes obviously compared to the regional stress field, affected by the impact of fault activity.The relationship between horizontal and vertical stress is σH>σh>σV at the measurement depth.The study reveals that the stress state is conducive to the activities of reverse fault and is basically the same as the geological data.By using sliding friction Coulomb Guidelines and friction strength from 0.6 to 1.0, it can be seen that present stress state near the fault has reached or exceeded the sliding friction threshold of the thrust fault, indicating that present tectonic activity is mainly thrust movement and it is impossible for the strike-slip movement to occur in the measured area.The thrust fault activity is less likely in the eastern section of the fault but much more likely in western part of the Qingchuan fault.
COUPLING BETWEEN ENDOGENIC AND EXOGENIC GEOLOGICAL PROCESSES IN THE WENCHUAN EARTHQUAKE AND EXAMPLE ANALYSIS OF GEO-HAZARDS
ZHANG Yong-shuang, SHI Ju-shong, SUN Ping, YAO Xin
2009, 15(2): 131-141.
Abstract (225) HTML (141) PDF (3337KB)(20)
Abstract:
The endogenic and exogenic geological processes are two indispensable processes for geo-hazard occurrence.However, only was exogenic geological process widely emphasized in the past, while the coupling between endogenic and exogenic geological processes were only presented in formations of experiential judges and qualitative studies.The MS8.0 Wenchuan earthquake provides a good chance to further study coupling processes between endogenic and exogenic geologic processes when it resulted in inestimable casualties and property losses.This paper summarizes the general manifestations of coupling processes in mountainous area, e.g.the couplings between active fault and weathering, rock-soil mass structure and deformation failure, geomorphology and seismic force, seismic force and groundwater.An analysi has been made on the relationships between various geological processes and their results during seismic landslide occurrence, which will be of certain guiding significance for understanding seismic geo-hazard mechanism and its development regularity.
A CONSIDERATION ON REGIONAL CRUSTAL STABILITY ASSESSMENT AFTER MS8.0 WENCHUAN STRONG EARTHQUAKE IN CHINA
TAN Cheng-xuan, SUN Ye, WU Shu-ren, HAN Jin-liang, WU Fang, SUN Wei-feng
2009, 15(2): 142-150.
Abstract (145) HTML (81) PDF (1269KB)(7)
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A new consideration and knowledge on regional crustal stability assessment was awoken by the MS8. 0 Wenchuan earthquake in China. This paper thoroughly introduces the basic theories of regional crustal stability assessment in China, including 'safety island' theory, geological texture control theory, regional stability engineering geology theory and 'field' theory, and the systemic, hierarchical, quantitative and intelligent methodology and technology. In order to better serve engineering construction, the regional stability evaluation develop towards micro-zonation and 4-dimension level.At last, the regional crustal stability assessment standards of People’ s Republic of China should be afforded and published to establish regional crustal stability assessment system in China. Meanwhile, the regional crustal stability assessment zonation map of China should be compiled to build up the regional crustal stability national platform and to be adopted as the standards for land plan and engineering safety construction.
CO-SEISMIC DEFORMATION OF "5.12" WENCHUAN EARTHQUAKE BASED ON D-INSAR
YAO Xin, ZHANG Yong-shuang
2009, 15(2): 151-161.
Abstract (188) HTML (101) PDF (3587KB)(5)
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Co-seismic deformation is important original information to determine seismogenic faults, to understand mechanism of earthquake, to analyze fault movement, to evaluate the earthquake property lo sses as well as to discover the trend of future earthquakes. However, ways to survey co-seismic deformation are unable to quickly and comprehensively capture this kind of information. Therefore, a new spatial surveying method, D-InSAR (i. e. Differential Interferometry SAR), is highlighted. This paper presents D-InSAR principle and reviews progress of D-InSAR applied to co-seismic deformation observation, then qualitatively analyzes characteristics of D-InSAR image about " 5.12" Wenchuan earthquake. Results show that many geological phenomena, surface ruptures, change of fault dip angle, vertical displacement of two plates alone fault and distribution of huge geo-hazards, are highly related with D-InSAR image.
TECTONIC DEFORMATION FEATURES OF SHENNONGJIA REGION IN EASTERN DABASHAN FORELAND STRUCTURAL BELT
LI Jian-hua, ZHANG Yue-qiao, SHI Wei, LI Hai-long, DONG Shu-wen
2009, 15(2): 162-177.
Abstract (162) HTML (85) PDF (5475KB)(7)
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Shennongjia is located in the eastern part of Dabashan foreland arc-shaped structural belt. With the Yangri fault as a boundary, this region can be divided into the northern and southern parts. The northern part is characterized by W-E trending basement-involved detachment and cover folding, with the Palaeozoic cover closely folded. The southern part, named Shennongjia basement uplift, has different deformation features in the periphery, with deformation weak in northern margin but strong in the eastern one. As to this uplift, there are skirt-like fold structures in its western and southern margins, and the southern ones were characterized by fold hinge with large plunge angle. From the field analysis of fault kinematics and paleo-tectonic stress inversion from slip vectors, we can see that the region was mainly controlled by S - N compression stress field, but the stress field of the eastern margin was changed into NW -SE because of the compression from Shennongjia and Huangling uplift. Regional structural analysis and comparison showed that the eastern part of Dabashan foreland structural belt experienced Indosian primary formation stage and Yanshan final formation stage, and the Shennongjia basement uplift played a role of restriction in the formation of Dabashan foreland arc-shaped structural belt. The research on the deformation of Shennongjia has great significance to understanding the formation and evolution of the Dabashan foreland arc-shaped structural belt.
STRUCTURAL FEATURES AND TECTONIC EVOLUTION OF THE WEI-ZI-LUO FAULT ZONE IN SOUTHWESTERN GUIZHOU PROVINCE
ZHANG Rong-qiang, ZHOU Yan, WANG Xin-wei, LI Shuang-jian, LI Song
2009, 15(2): 178-189.
Abstract (217) HTML (98) PDF (3527KB)(30)
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The Wei-Zi-Luo fault develops in southwestern margin of the Yangtze block. This is a deep crustal fault zone and controls the deposition and deformation styles of the region. Based on detailed field observations, fluid inclusion analysis and temperature measurements, and using cross section balance, this paper describes structural texture and segmentation feature of the fault zone and discusses its tectonic evolution. The results show that the Wei-Zi-Luo fault zone consists of several segments with kinematics dominated by reverse and sinistral strike-slip motion.Fluid inclusion analysis indicates brittle environment of deformation occurring in the upper crust, with temperature less than 200 ℃. Restoration of cross section shows that this fault zone was under extension during the Early Devonian to Middle Triassic, which controlled the depositional sequence of the region. It was deformed during the Indosinian orogen at the end of Triassic. The major deformation phase, related to westward push of the South China Block, occurred in Late Jurassic to Early Cretaceous.
CHARACTERISTICS OF FAULTS IN THE PU-WEI RING DEPRESSION AND ITS CONTRIBUTION TO MIGRATION AND ACCUMULATION OF OIL AND GAS
LIU Wei, YU Chuan-mou
2009, 15(2): 190-200.
Abstract (143) HTML (92) PDF (1701KB)(5)
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The Pu-Wei ring depression, with complex structures, has been poorly studied. Based on analysis on the faults, this paper deals with function of the faults in migration and accumulation of oil and gas. The research demonstrates that both the Pucheng-Chenying fault zone and the Weidong-Wendong fault zone consist of five master control faults, which control the structural formwork and migration and accumulation of oil and gas. The activity of such faults as Weidong, Wendong, Pucheng, Pu31 lasted a long period and match well with oil accumulation in age. The faults serve as a prominent way for oil migration from deep zone to superficial part. The faults and sand bodies of good connectivity, as the main migration pathway, together constitute the fault-type and fault-sand-type transforming system for oil and gas. The fault-type transforming system connects souce rock and reservoir and enhances the ability of vertical oil migration; and the fault-sand-type is chiefly helpful to lateral transforming. The faults block or regulate migration and its direction, leading to the formation of structural-stratigraphic hydrocarbon reservoir near the main faults and formation of lithologic hydrocarbon reservoir at the edge far away the main faults.
STUDY ON THE TECHNOLOGY AND METHOD OF 3D GEOLOGICAL MODELING: A CASE STUDY OF THE EAST KUNLUN OROGENIC BELT
ZHANG Si-ke, NI Jin-yu, GAO Wan-li, HU Dao-gong
2009, 15(2): 201-208.
Abstract (175) HTML (108) PDF (1714KB)(13)
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The key technology of 3D geological modeling is how to make use of professional GIS platform, which can truly get the reappearance of 3D geological entities and spatial analysis, to provide technical support of geological research and exploration of mineral resources. In this paper, taking the east Kunlun orogenic belt as object and using Micromine software system, the authors have studied and summarized the key technology and methods of 3D geological modeling.