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Du J.,Chinese Academy of Geological Sciences | Du J.,Key Laboratory of Neotectonic Movement & Geohazard | Qin X.,Chinese Academy of Geological Sciences | Qin X.,Key Laboratory of Neotectonic Movement & Geohazard | And 7 more authors.
Engineering Geology | Year: 2017

The Alxa area is a candidate site for China's high-level radioactive waste (HLW) repository. In-situ stress measurements using hydraulic fracturing were performed to directly estimate the present-day stress field of the Alxa area. Variation of the in-situ stress components with depth in two sub-sites (i.e., Nuorigong, and Tamusu) was analyzed based on valid hydraulic fracturing data obtained from two sub-vertical boreholes. The results reveal that the horizontal stresses in the Alxa area present an intermediate or low level. The in-situ stress magnitudes are consistent within the crustal frictional strength range that predicated using the Coulomb frictional-failure theory incorporating frictional coefficients of approximately 0.6–1.0. The maximum horizontal stress in the Alxa area is dominantly oriented in the NNE–SSW direction which is consistent with the direction of the tectonic stress field of northwest China. The estimation of the in-situ stress measurement results provides critical knowledge of the engineering geological characteristics of this candidate area, and support on potential underground excavation. © 2017 Elsevier B.V.

Zhang C.-Y.,Key Laboratory of Neotectonic Movement & Geohazard | Zhang C.-Y.,Chinese Academy of Geological Sciences | Wang Z.-F.,China National Offshore Oil Corporation | Fan T.-Y.,Key Laboratory of Neotectonic Movement & Geohazard | And 7 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

In order to understand the stress field characteristics and carry out geodynamic study of South China Sea, the Xike 1A well, located in Shidao of Xisha Islands was drilled for hydraulic fracturing in situ stress measurement. Using in situ stress test results in shallow basement of Shidao of Xisha Islands, combined with other geophysics data, the geodynamic background and force source of basin expansion are analyzed. In situ stresses were measured by using hydraulic fracturing method with the standard equipment and procedure suggested by International Society for Rock Mechanics (ISRM). The critical pressure parameter, shut-in pressure (Ps), was processed and determined with the single tangent method, dp/dt method, dt/dp method, and Muskat method. The orientation of the maximum horizontal principal stress was determined by impression technique. Additionally, some representative rock specimens from the 1153.14~1267.5 m were selected to make rock thin sections for observation and determination of rock microstructure and characteristics near the shallow basement. The 1268.07 m-deep Xike 1A well revealed an about 1257.52 m-deep sedimentary cover that mainly consists of bioclastic limestone, marbleized limestone, and dense sedimentary marble, and reached the shallow basement which consists of quartz diorite and granite. In this borehole, we conducted hydraulic fracturing stress measurements at 5 depth intervals between 1125.8~1262.0 m, and obtained the maximum horizontal principal stresses of 17.09~20.85 MPa, the minimum horizontal principal stresses between 15.97~18.29 MPa, and the estimated vertical principal stresses between 22.86~26.68 MPa. The feature of crustal stresses is SV>SH>Sh and the vertical principal stress plays a dominant role, which is prone to the activity of normal fault. Influenced by faults around the Xisha Trough, crustal stress level is relatively low. Impression tests show that the orientations of the maximum horizontal principal stresses in basement of Xisha Islands are from nearly EW to NW. The dominant direction, NWW, coincides well with existing GPS measurements, shear wave splitting measurements, and surface wave inversion data, which show the well consistency of lithosphere deformation of Xisha Islands. The feature of crustal stress implies that the crust basement of Xisha Islands is in an extensional stress environment. Crustal stress field here is jointly constrained by plate movements and upwelling of the Earth's mantle material of Northwestern South China Sea. Analysis from measured in situ stress data of Northwestern South China Sea indicates that the regional principal stress orientations are similar and hence, this region is during in a uniform and stable background of tectonic movement. ©, 2015, Science Press. All right reserved.

Zhang P.,Chinese Academy of Geological Sciences | Zhang P.,Key Laboratory of Neotectonic Movement & Geohazard | Hu Q.-Y.,China Geological Survey | Feng C.-J.,Chinese Academy of Geological Sciences | And 5 more authors.
Acta Geoscientica Sinica | Year: 2015

To explore the in-situ stress in the Changle-Nan'ao fracture belt and its present activity, the authors gathered data from 21 segments for in-situ stress measurement and from 4 segments for orientation of major principal stress varying intervals along the drill hole with total depth of 600 m located inside a granite-rich region in the northern part of Quanzhou City. Combined with the high in-situ stress data of SH>Sh>Sv, the core sampling of the structure features of shallow earth crust rock formation reveals that current horizontal principal stresses play a leading role in reverse fault activity. Moreover, measured maximum principal in-situ stress strikes in NWW direction and reflects present compressive properties, with dextral slip activity, of the middle segment. Calculated through measured principal stresses, the magnitudes of feature parameters µm and R reach 0.44~0.76 and 0.44~0.65 respectively, which reflect the high-stress accumulative capability of the regional crust and availability for the activity of fault movement in this area. The measured results indicate that the state of in-situ stress has reached the critical value, the activity of the fault is approaching the critical state, and the potential risk of the reverse fault has the tendency of sliding and shearing failure. With pre-existing research result, these new dynamic data will allow us to open new research avenues for understanding the present active features of the middle segment of the Changle-Nan'ao fracture belt and to provide a basic guarantee for the earthquake research and urban safety. ©, 2015, Science Press. All right reserved.

Feng C.,Chinese Academy of Geological Sciences | Feng C.,Key Laboratory of Neotectonic Movement & Geohazard | Chen Q.,Chinese Academy of Geological Sciences | Chen Q.,Key Laboratory of Neotectonic Movement & Geohazard | And 8 more authors.
Journal of Earth Science | Year: 2014

After the Wenchuan MS 8.0 Earthquake, which occurred on May 12, 2008, in Sichuan Province, China, we conducted a series of hydraulic fracturing stress measurements in three 200 m deep boreholes (ZK01, ZK02, and ZK03) drilled in Beichuan and Jiangyou regions near the northeastern segment of Longmenshan fault belt in 2009. These measurements revealed the near-surface stress field in the fault region one year after the Wenchuan MS 8.0 Earthquake. However, the lack of the stress measurements before the earthquake in the same region makes it difficult to understand variations of the in situ stress field (near-surface) by comparative analysis. In order to determine the unknown horizontal principal stresses before the earthquake in Beichuan and Jiangyou regions, the following research method was tentatively applied. Firstly, we calculate the static co-seismic stress field by linear elastic finite element numerical simulation with ANSYS, based on the co-seismic static displacement generated by the Wenchuan MS 8.0 Earthquake along the central Longmenshan fault plane in Beichuan and Jiangyou. Secondly, combining hydraulic fracturing measurements (after the earthquake) with the co-seismic stress (simulation), the magnitudes and orientations of horizontal principal stresses before the earthquake were calculated. Finally, the variation of the in situ stress (near-surface) in Beichuan and Jinagyou, both before and after the Wenchuan MS 8.0 Earthquake, were obtained by comparative analysis. To do this the magnitude of SHmax was decreased on average by 13.01 and 6.54 MPa after the earthquake in ZK02 and ZK03, respectively and the magnitude of SHmin was decreased by 2.54 and 5.29 MPa in ZK02 and ZK03, respectively. Following the earthquake, the average direction of SHmax rotated anticlockwise by 42.5°. © 2014, China University of Geosciences and Springer-Verlag Berlin Heidelberg.

Li C.,Chinese Academy of Geological Sciences | Li C.,Key Laboratory of Neotectonic Movement & Geohazard | Wang S.,Chinese Academy of Geological Sciences | Wang S.,Key Laboratory of Neotectonic Movement & Geohazard | And 5 more authors.
Geological Bulletin of China | Year: 2015

The Longjie silt layer consists of a series of silt, silty clay and clay lacustrine sediments which are grayish black, grayish yellow and grayish white in color. This silt layer is distributed along the valley of the Jinsha River from Sanduizi of Panzhihua City to Baimakou of Wuding County, and is well developed in the Longjie basin in Yunnan Province. The Longjie drill hole intersects the stratatigraphic thickness of 101.18 m, which includes 92.96 m Longjie silt layer. Its sedimentation occurred about 150~30 ka BP, as shown by the analysis of magnetostratigraphy and OSL dating. Through the study of sedimentary variation characteristics, this paper deals with the formation process of Longjie silt layer, the relative regional neotectonics movement stage and its influence on the development of the Jinsha River. ©, 2015, China Geological Survey. All right reserved.

Zhang C.-S.,Chinese Academy of Geological Sciences | Zhang C.-S.,Key Laboratory of Neotectonic Movement & Geohazard | Wu M.-L.,Chinese Academy of Geological Sciences | Wu M.-L.,Key Laboratory of Neotectonic Movement & Geohazard | And 5 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2016

This paper presents the values and the directions of present-day stress measured at different sites in the Chnagbaishan Mountains of Jilin Province. In order to understand the current state of stress in the Changbaishan Mountains and meet demand of volcanic monitoring, the in-situ stress measurement was carried in this region. These data may be the first measurement results in the Changbaishan region. The measurement sites were located at different tectonic positions, including Dongqing village of Yongqing town (Antu county), Binghutun village of Songjianghe town (Antu county) and Daqingchuan village of Xianrenqiao town (Fusong county), and the measurement was made at depths from 40 m to 95 m using the method of hydraulic fracturing. The results indicate that the direction of maximum principal stress is mainly NW-NNW in the north of Tianchi and EW in the West of Tianchi. The values of maximum principal stress were between 2.31 and 13.9 MPa, which are high or middle compared with that obtained elsewhere in China. And the values of minimum principal stress were between 1.39 and 7.02 MPa. Based on these results, the state analysis of current stress was carried out for the region of Changbaishan Mountains. The state of present-day stress in this region is very complexity, because it was influenced by regional structure, magmatic movement and the geothermal field of Tianchi. © 2016, Science Press. All right reserved.

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