Using GPS observations of horizontal movement from 2001 to 2003 and the cross-fault mobile short-levelling data of 1988～2003, and with the aid of the improved negative dislocation model and the time-varying curve of ...Using GPS observations of horizontal movement from 2001 to 2003 and the cross-fault mobile short-levelling data of 1988～2003, and with the aid of the improved negative dislocation model and the time-varying curve of strain intensity ratio of fault deformation, the regional tectonic deformation background and medium- and short-term precursors related to the preparation of the Minle-Shandan earthquakes of M S6.1 and M S5.8 on October 25, 2003 are investigated. The results reveal that, under the background of the wide-range deformation adjustment, short-term relaxation and recovery caused by the Kunlun Mountains earthquake of M S8.1, the hypocenters of the earthquakes are located on the north edge of the shear stress enhancement zone between the compressional locked segments of block boundary fault, a place which may represent an accelerated strain accumulation. An obvious anomaly of strain intensity ratio appeared in short-levelling measurements crossing over the fault at the Shihuiyaokou site, the closest to the epicenters, 3 months before the occurrence of the earthquakes. In addition, the variation in number of anomalies from 10-odd days to months before the earthquakes in the entire monitoring area and the anomaly concentration and local enhancement relative to near source in the 3 months before the earthquakes are regarded to be precursors to the two events.展开更多
Using GPS observation data for the middle segment of the Fenwei seismic zone during the time period of 1996 ～ 2001, the velocity field of crustal movement is calculated. Thus, the vectors of relative horizontal movem...Using GPS observation data for the middle segment of the Fenwei seismic zone during the time period of 1996 ～ 2001, the velocity field of crustal movement is calculated. Thus, the vectors of relative horizontal movement between measuring points in the region are also obtained. Adopting a deformation model of homogeneous elastic body, the principal strain rate parameters of deformation units are calculated. A method is introduced to calculate the rate of seismic moment accumulation due to crustal deformation. The problems of using this rate to analyze the tendency of seismicity in the zone, and to estimate the recurrence interval of large earthquakes in the potential seismic source areas（PSSA） are discussed. The results show that the rate of seismic moment accumulation in the middle segment of the Fenwei zone is 4.22 x 1017 Nm/a, which is much higher than the average release rate of seismic moment in the current activity period. This means that the belt is now in a stage of seismic strain accumulation and that the seismicity would become stronger in the future than now. The results of estimation of the recurrence interval of large earthquakes in the Dingxiang and Huozhou PSSA are close to the results obtained from studying active faults. This implies that the use of the proposed estimation method is worthy of further investigation. In particular, it is of greater practical significance for those regions that have shorter history of earthquake records or lower degree of active structure study.展开更多
The dynamics of high-altitude inland lakes in the Tibetan Plateau are sensitive indicators of climate change. Due to the remoteness and hard access, satellite altimetry becomes an effective approach to obtaining large...The dynamics of high-altitude inland lakes in the Tibetan Plateau are sensitive indicators of climate change. Due to the remoteness and hard access, satellite altimetry becomes an effective approach to obtaining largescale and temporally continuous information of lake-level changes. The CryoSat-2 altimetry is expected to solve the current problem that earlier radar altimeters are only practical for monitoring large water bodies, while ICESat laser altimetry is available only for the period 2003-2009. In this study, the comparison of CryoSat-2 altimetry for Namco with in situ water-level data suggests a high cor- relation coefficient of 0.71 （P 〈 0.01）, with the mean error of -0.12 m and root-mean-square error of 0.18 m. Further, the combination of ICESat and CryoSat-2 altimetry data and in situ lake-level observations reveals a rapid water- level rise of 0.24 4- 0.04 m/year during 2003-2008 and then a slightly decreasing trend of -0.09 4- 0.04 m/year during 2009-2013. This study suggests that the CryoSat-2 altimetry has the potential of sustaining the fine observa- tions on Tibetan lakes, following the ICESat mission. Besides, the examination of four key climatic variables （temperature, precipitation, potential evapotranspiration, and relative humidity） during 1990-2013 indicates that the wetting climate over Namco Basin stagnated or even reversed around 2006, which may be tightly related to the slowing lake growth.展开更多
文摘Using GPS observations of horizontal movement from 2001 to 2003 and the cross-fault mobile short-levelling data of 1988～2003, and with the aid of the improved negative dislocation model and the time-varying curve of strain intensity ratio of fault deformation, the regional tectonic deformation background and medium- and short-term precursors related to the preparation of the Minle-Shandan earthquakes of M S6.1 and M S5.8 on October 25, 2003 are investigated. The results reveal that, under the background of the wide-range deformation adjustment, short-term relaxation and recovery caused by the Kunlun Mountains earthquake of M S8.1, the hypocenters of the earthquakes are located on the north edge of the shear stress enhancement zone between the compressional locked segments of block boundary fault, a place which may represent an accelerated strain accumulation. An obvious anomaly of strain intensity ratio appeared in short-levelling measurements crossing over the fault at the Shihuiyaokou site, the closest to the epicenters, 3 months before the occurrence of the earthquakes. In addition, the variation in number of anomalies from 10-odd days to months before the earthquakes in the entire monitoring area and the anomaly concentration and local enhancement relative to near source in the 3 months before the earthquakes are regarded to be precursors to the two events.
文摘Using GPS observation data for the middle segment of the Fenwei seismic zone during the time period of 1996 ～ 2001, the velocity field of crustal movement is calculated. Thus, the vectors of relative horizontal movement between measuring points in the region are also obtained. Adopting a deformation model of homogeneous elastic body, the principal strain rate parameters of deformation units are calculated. A method is introduced to calculate the rate of seismic moment accumulation due to crustal deformation. The problems of using this rate to analyze the tendency of seismicity in the zone, and to estimate the recurrence interval of large earthquakes in the potential seismic source areas（PSSA） are discussed. The results show that the rate of seismic moment accumulation in the middle segment of the Fenwei zone is 4.22 x 1017 Nm/a, which is much higher than the average release rate of seismic moment in the current activity period. This means that the belt is now in a stage of seismic strain accumulation and that the seismicity would become stronger in the future than now. The results of estimation of the recurrence interval of large earthquakes in the Dingxiang and Huozhou PSSA are close to the results obtained from studying active faults. This implies that the use of the proposed estimation method is worthy of further investigation. In particular, it is of greater practical significance for those regions that have shorter history of earthquake records or lower degree of active structure study.
基金supported by the National Special Basic Research Project of the Ministry of Science and Technology(2013FY111400-2,2009CB723901)the National Natural Science Foundation of China(41120114001,41125003,41071254,40971048)+3 种基金the European Space Agency(ESA AO 2605)the Knowledge Innovation Foundation Program for outstanding Young Scholar of Chinese Academy of Sciences(CAS)(KZCX2-EWQN104)supported by Open Research Fund of Key Laboratory of Tibetan Environmental Changes and Land Surface Processes in Chinese Academy of SciencesOpen Fund of State Key Laboratory of Remote Sensing Science
文摘The dynamics of high-altitude inland lakes in the Tibetan Plateau are sensitive indicators of climate change. Due to the remoteness and hard access, satellite altimetry becomes an effective approach to obtaining largescale and temporally continuous information of lake-level changes. The CryoSat-2 altimetry is expected to solve the current problem that earlier radar altimeters are only practical for monitoring large water bodies, while ICESat laser altimetry is available only for the period 2003-2009. In this study, the comparison of CryoSat-2 altimetry for Namco with in situ water-level data suggests a high cor- relation coefficient of 0.71 （P 〈 0.01）, with the mean error of -0.12 m and root-mean-square error of 0.18 m. Further, the combination of ICESat and CryoSat-2 altimetry data and in situ lake-level observations reveals a rapid water- level rise of 0.24 4- 0.04 m/year during 2003-2008 and then a slightly decreasing trend of -0.09 4- 0.04 m/year during 2009-2013. This study suggests that the CryoSat-2 altimetry has the potential of sustaining the fine observa- tions on Tibetan lakes, following the ICESat mission. Besides, the examination of four key climatic variables （temperature, precipitation, potential evapotranspiration, and relative humidity） during 1990-2013 indicates that the wetting climate over Namco Basin stagnated or even reversed around 2006, which may be tightly related to the slowing lake growth.
