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| 1 | Preliminary Results of In-situ Stress Measurements along the Longmenshan Fault Zone after the Wenchuan M_s 8.0 Earthquake显示文摘Four months after the Wenchuan M_s 8 earthquake in western Sichuan,China,in situ stress measurements were carried out along the Longmenshan fault zone with the purpose of obtaining stress parameters for earthquake hazard assessment.In-situ stresses were measured in three new boreholes by using overcoring with the piezomagnetic stress gauges for shallow depths and hydraulic fracturing for lower depths.The maximum horizontal stress in shallow depths(~20 m) is about 4.3 MPa,oriented N19°E,in the epicenter area at Yingxiu Town,about 9.7 MPa,oriented N51°W,at Baoxing County in the southwestern Longmenshan range,and about 2.6 MPa,oriented N39°E,near Kangding in the southernmost zone of the Longmenshan range.Hydraulic fracturing at borehole depths from 100 to 400 m shows a tendency towards increasing stress with depth.A comparison with the results measured before the Wenchuan earthquake along the Longmenshan zone and in the Tibetan Plateau demonstrates that the stress level remains relatively high in the southwestern segment of the Longmenshan range,and is still moderate in the epicenter zone.These results provide a key appraisal for future assessment of earthquake hazards of the Longmenshan fault zone and the aftershock occurrences of the Wenchuan earthquake. | WU Manlu ZHANG Yueqiao LIAO Chunting CHEN Qunce MA Yinsheng WU Jinsheng YAN Junfeng OU Mingyi | 2009 | Acta Geologica Sinica(English Edition)2009，83，4： | 31 |
| 2 | Co-seismic Faults and Geological Hazards and Incidence of Active Fault of Wenchuan Ms 8.0 Earthquake,Sichuan,China显示文摘There are two co-seismic faults which developed when the Wenchuan earthquake happened. One occurred along the active fault zone in the central Longmen Mts.and the other in the front of Longmen Mts.The length of which is more than 270 km and about 80 km respectively.The co-seismic fault shows a reverse flexure belt with strike of N45°-60°E in the ground,which caused uplift at its northwest side and subsidence at the southeast.The fault face dips to the northwest with a dip angle ranging from 50°to 60°.The vertical offset of the co-seismic fault ranges 2.5-3.0 m along the Yingxiu-Beichuan co-seismic fault,and 1.5-1.1 m along the Doujiangyan-Hanwang fault.Movement of the coseismic fault presents obvious segmented features along the active fault zone in central Longmen Mts. For instance,in the section from Yingxiu to Leigu town,thrust without evident slip occurred;while from Beichuan to Qingchuan,thrust and dextral strike-slip take place.Main movement along the front Longmen Mts.shows thrust without slip and segmented features.The area of earthquake intensity more thanⅨdegree and the distribution of secondary geological hazards occurred along the hanging wall of co-seismic faults,and were consistent with the area of aftershock,and its width is less than 40km from co-seismic faults in the hanging wall.The secondary geological hazards,collapses,landslides, debris flows et al.,concentrated in the hanging wall of co-seismic fault within 0-20 km from co-seismic fault. | MA Yinsheng LONG Changxing TAN Chengxuan WANG Tao GONG Mingquan LIAO Chunting WU Manlu SHI Wei DU Jianjun PAN Feng | 2009 | Acta Geologica Sinica(English Edition)2009，83，4： | 7 |
| 3 | Piezomagnetic In-situ Stress Monitoring and its Application in the Longmenshan Fault Zone显示文摘The relative change of in-situ stress is an inevitable outcome of differential movement among the crust plates. Conversely, changes of in-situ stress can also lead to deformation and instability of crustal rock mass, trigger activity of faults, and induce earthquakes. Hence, monitoring real-time change of in-situ stress is of great significance. Piezomagnetic in-situ stress monitoring has good and longtime applications in large engineering constructions and geoscience study fields in China. In this paper, the new piezomagnetic in-situ stress monitoring system is introduced and it not only has overall improvements in measuring cell's structure and property, stressing and orienting way, but also enhances integration and intelligence of control and data transmission system, in general, which greatly promotes installing efficiency of measuring probe and quality of monitoring data. This paper also discusses the responses of new piezomagnetic system in large earthquake events of in-situ stress monitoring station at Qiaoqi of Baoxing and Wenxian of Gansu. The monitoring data reflect adjustments and changes of tectonic stress field at the southwestern segment of and the northern area near the Longmenshan fault zone, which shows that the new system has a good performance and application prospect in the geoscience field. Data of the Qiaoqi stress-monitoring station manifest that the Lushan Earthquake did not release stress of the southwestern segment of the Longmenshan fault zone adequately and there still probably exists seismic risk in this region in the future. Combined with absolute in-situ stress measurement, carrying out long-term in-situ stress monitoring in typical tectonic position of important regions is of great importance for researchers to assess and study regional crust stability. | ZHANG Chongyuan WU Manlu CHEN Qunce LIAO Chunting | 2014 | Acta Geologica Sinica(English Edition)2014，88，5： | 4 |
| 4 | Tectonic Stress State Changes Before and After the Wenchuan M_s 8.0 Earthquake in the Eastern Margin of the Tibetan Plateau显示文摘Crustal tectonic activities are essentially the consequences of the accumulation and release of in situ stress. Therefore, studying the stress state near active faults is important for understanding crustal dynamics and earthquake occurrences. In this paper, using in situ stress measurement results obtained by hydraulic fracturing in the vicinity of the Longmenshan fault zone before and after the Wenchuan Ms 8.0 earthquake and finite element modeling, the variation of stress state before and after the Wenchuan Ms 8.0 earthquake is investigated. The results show that the shear stress, which is proportional to the difference between principal stresses, increases with depth and distance from the active fault in the calm period or after the earthquakes, and tends to approach to the regional stress level outside the zone influenced by the fault. This distribution appears to gradually reverse with time and the change of fault properties such as frictional strength. With an increase in friction coefficient, low stress areas are reduced and areas with increased stress accumulation are more obvious near the fault. In sections of the fault with high frictional strengths, in situ stress clearly increases in the fault. Stress accumulates more rapidly in the fault zone relative to the surrounding areas, eventually leading to a stress field that peaks at the fault zone. Such a reversal in the stress field between the fault zone and surrounding areas in the magnitude of the stress field is a potential indicator for the occurrence of strong earthquakes. | MENG Wen CHEN Qunce WU Manlu FENG Chengjun QIN Xianghui | 2015 | Acta Geologica Sinica(English Edition)2015，89，1： | 3 |
| 5 | Crustal Stress State and Seismic Hazard along Southwest Segment of the Longmenshan Thrust Belt after Wenchuan Earthquake显示文摘The crustal stress and seismic hazard estimation along the southwest segment of the Longmenshan thrust belt after the Wenchuan Earthquake was conducted by hydraulic fracturing for in-situ stress measurements in four boreholes at the Ridi, Wasigou, Dahegou, and Baoxing sites in 2003, 2008, and 2010. The data reveals relatively high crustal stresses in the Kangding region(Ridi, Wasigou, and Dahegou sites) before and after the Wenchuan Earthquake, while the stresses were relatively low in the short time after the earthquake. The crustal stress in the southwest of the Longmenshan thrust belt, especially in the Kangding region, may not have been totally released during the earthquake, and has since increased. Furthermore, the Coulomb failure criterion and Byerlee's law are adopted to analyzed in-situ stress data and its implications for fault activity along the southwest segment. The magnitudes of in-situ stresses are still close to or exceed the expected lower bound for fault activity, revealing that the studied region is likely to be active in the future. From the conclusions drawn from our and other methods, the southwest segment of the Longmenshan thrust belt, especially the Baoxing region, may present a future seismic hazard. | Xianghui Qin Chengxuan Tan Qunce Chen Manlu Wu Chengjun Feng | 2014 | Journal of Earth Science2014，25，4： | 2 |
| 6 | 1 Kunlun earthquake显示文摘 | LIAO CHUNTING ZHANG CHUANSHAN WU MANLU Stress change near the Kunlun fault before and after Ms 8 | 2003 | Geo- physical Research Letters2003，30，20： | 1 |
| 7 | A Preliminary Study on the Present Crustal Stress of Northern South China Sea显示文摘The South China Sea(SCS)is the largest marginal sea in West Pacific formed by a combined effect of the Eurasian plate,Pacific plate and India-Australian plate,and is thus considered to be a unique natural laboratory to study oceanic dynamics and tectonic evolutions(Xie et al.,2006;Luan and Zhang,2009).Besides,the SCS contains enormous petroleum resources for its favorable conditions of oil-gas generation,accumulation and preservation.It is therefore imperative to intensively study the marine | CHEN Qunce MENG Wen WU Manlu FAN Taoyuan ZHANG Chongyuan QIN Xianghui LI Guoqi | 2015 | Acta Geologica Sinica(English Edition)2015，89，1： | 0 |
| 8 | Reexamining the Seismological Implications of the Present-day Stress State of the Yingxiu-Beichuan Fault after the Wenchuan Earthquake显示文摘The present-day stress state of the Yingxiu-Beichuan fault after the Wenchuan earthquake was re-estimated using measured in-situ stress data obtained after the Wenchuan earthquake. The results reveal that the gradient coefficients of principal stresses versus depth decrease from south to north along the Yingxiu-Beichuan fault, revealing that the stress level decreases from south to north. The consistency between the present-day stress levels and surface ruptures generated during the earthquake indicates that the accumulated tectonic stress beneath the Yingxiu-Beichuan fault before the Wenchuan earthquake was relieved in form of surface ruptures. This resulted in the stress remaining high in the southern section of the Yingxiu-Beichuan fault but relatively low in the northern section. Abnormal high pore pressure conditions and an extremely low frictional coefficient play important role in the interpretation of the stress field adjustment and seismic events observed after the Wenchuan earthquake along this fault, according to the estimation results using the Coulomb frictional-failure theory incorporating frictional coefficients ranging from 0.4 to 1.0. To accurately estimate the seismological hazard of the Yingxiu-Beichuan fault by analyzing fault instability using the Coulomb frictional-failure theory, much attention should be focused on the pore pressure conditions and the evolution state of the frictional coefficient under the present-day stress state. | QIN Xianghui CHEN Qunce FENG Chengjun DU Jianjun WU Manlu MENG Wen SUN Dongsheng | 2016 | Acta Geologica Sinica(English Edition)2016，90，2： | 0 |
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