Based on the data from 4 times of repeated measurements (1996-1999) of GPS monitoring network arranged along Shanxi fault zone, the current horizontal movement of Shanxi fault zone and its relationship with Yangyuan-H...Based on the data from 4 times of repeated measurements (1996-1999) of GPS monitoring network arranged along Shanxi fault zone, the current horizontal movement of Shanxi fault zone and its relationship with Yangyuan-Hunyuan earthquake (M=5.6; 39.8°N, 113.9°E; November 1, 1999) which occurred at the north part of the monitoring network is analyzed. The results from the analysis indicate: (1) The horizontal movement along Shanxi fault zone was not obvious from 1996 to 1997; (2) The intensity of horizontal movement along Shanxi fault zone increased at the period of 1997 to 1998, and there are three areas with relatively higher strain (1×10-6) appeared, i.e., the source region, Xinzhou region and northeastern part of Jiexiu; (3) Although the dominant movement direction of Shanxi fault zone in the period of 1998 to 1999 was consistent with the fault striking direction, but as compared with the movement in the passed year, the direction was almost reversed, while the absolute value of the movement was close each other; (4) The accumulated horizontal movement along Shanxi fault zone from 1996 to 1999 became obvious gradually. It can be divided into three parts by considering its tendency: (a) the dominant direction of movement in north of Xinzhou is NNE (0.8 cm); (b) in south of Quwo it is SSW (1 cm); (c) in the central area it is rather complicated, the deformation in the southern part is little more large, but in the view of whole area there is no dominant movement exist. Generally speaking, Shanxi fault zone is mainly controlled by the NNE-SSW-trending extension stress field, but there is no strike-slip movement. In the period of 1997 to 1998, there might be a clear stress disturb and it was essentially recovered in 1999. Then the Yangyuan-Hunyuan earthquake occurred. Very possible, this disturb is the triggering to the earthquake.展开更多
This paper makes a systematical study on characteristics of structure and motion of the tectonic blocks in northern part of the Shanxi fault depression zone by means of geometrical and kinematical analysis of the bloc...This paper makes a systematical study on characteristics of structure and motion of the tectonic blocks in northern part of the Shanxi fault depression zone by means of geometrical and kinematical analysis of the blocks. The ki-netic behavior of the blocks is discussed by comparing associated geomorphic features of fault movement. All analyses and studies are based on a Domino model. The block movement, fault basin extension and their regional distribution are systematically investigated. The result shows: (a) The studied region is divided into sub-regions by NW striking faults: the western, middle and eastern sub-region with crustal extension being 4.46 km, 2.80 km and 1.86 km, respectively. The extensional amount of each block in the region is estimated being generally about 1 km. The calculated result using the block motion model approximately fits the data of geologic survey. (b) Block kin-ematical features are obviously different between the northern and southern part, with the Hengshan block in be-tween, of the studied region. Moreover, the magnitude of the largest historical earthquake in the northern part is about 6, while that in the southern is 7. The faulted blocks in the northern sub-region show northwestward exten-sion, indicating a feature of extensional graben, while the blocks in the southern part manifest tilt motion, extend-ing southeastward, in the opposite sense of fault dipping. Additional tectonic stress generated by block rotation may be one of major factors affecting seismogenic process in the region. It is responsible for the difference in the movement of the block boundary faults and seismic activities between the two sub-regions.展开更多
The Shanxi rift zone is one of the largest and active Cenozoic grabens in the world, studying the velocity structure of the crust and upper mantle in this region may help us to understand the mechanisms of rift proces...The Shanxi rift zone is one of the largest and active Cenozoic grabens in the world, studying the velocity structure of the crust and upper mantle in this region may help us to understand the mechanisms of rift processes and the seismogenic environment of active seismicity in continental rifts. In this work, using the broadband seismic data of Shanxi, Hebei, Henan, Shaanxi provinces, and the Inner Mongolia Autonomous Region from February 2009 to November 2011, we have picked out 350 high-quality phase velocity dispersion curves of fundamental mode Rayleigh waves at periods from 8 to 75 s, and Rayleigh wave phase velocity maps have been constructed from 8 to 75 s period with horizontal resolution ranging from 40 to 50 km by two-station surface-wave tomography. Then, using a genetic algorithm, a 3D shear-wave speed model of the crust and uppermost mantle have been derived from these maps with a spatial resolution of 0.4° × 0.4°. Four characteristics can be outlined from the results： （1） Except in the Datong volcanic zone, in the depth range of 11-30 km, the location of a transition zone between the highand low-velocity regions is in agreement with the seismicity pattern in the study region, and the earthquakes are mostly concentrated near this transition zone; （2） In the depth range of 31-40 km, shear-wave velocities are higher to the south of the Taiyuan Basin and lower to the north, which is similar to the distribution pattern of Moho depth variations in the Shanxi region; （3） The shear-wave velocity pattern of higher velocities to the south of 38×N and lower velocities to the north is found to be consistent with that from the upper crustal levels to depth of 70 km. At the deeper depths, the spatial scale of the low-velocity anomalies zone in the north is gradually shrinking with depth increasing, the low-velocity anomalies are gradually disappearing beneath the Datong volcanic zone at the depth of 151-200 km. We proposed that the root of the Datong volcano may reach to a depth around 150 km; （4） Along the N-S vertical profile at 112.8°E, the 38°N latitude is the boundary between high and low velocities, arguing the tectonic difference between the Shanxi rift zone and its flanks, in the rift zone the seismic velocity is dominated by low-velocity anomalies while in the flanks it is high.展开更多
The tendency and dynamic characteristics of horizontal movement along the Shanxi fault zone have been analyzed using the data obtained from 6 repeated measurements (1996～2001) in the GPS monitoring network arranged a...The tendency and dynamic characteristics of horizontal movement along the Shanxi fault zone have been analyzed using the data obtained from 6 repeated measurements (1996～2001) in the GPS monitoring network arranged along the Shanxi fault zone. The results indicate: (1) the tendentious activity of the present stage is characterized by a W trending movement along the northern segment of the zone, an E trending movement along the southern segment and counter clockwise differential activity on the whole, but the intensity of the tendentious activity is not high. The tendentious differential movement is only about 3 mm/a in the direction perpendicular to the fault zone from the south to the north, and its stretch in the SN direction is only 1 mm/a and mainly occurs along the north segment of the fault; (2) The azimuth of the principal compressive stress field reflected by the tendentious movement is 72°; (3) The property of annual activity is not the same, even contrary to one another or deviates from the tendentious activity. Therefore, the parameters of the strain field derived from them dont reflect the physical characteristics of the basic stress field. (4) The high frequency movement (yearly) does not only exist but is also complicated by an intensity several times higher than that of the tendentious movement; (5) Obvious differential movements, including strike slip, can not be seen in either in secular activity or annual activity on both sides of any fault. The tendentious movement not only verifies the conjecture of “strong in the south and weak in north”, which is the basic feature forcing the western boundary of the North China area, but it also extends to the hinterland of North China. The fact that there is no obvious differential activity on both sides of the fault might indicate that the differential activity among the intraplate blocks is completed by gradual variation in a certain space, rather than the abrupt change bordered by a fault or narrow stripe zone. The obvious dynamic activity might indicate: (1) there is stress disturbance in the basic stress field; (2) the inhomogeneous or non synchronous variation that appeared in the regional stress and strain fields was due to the different physical property of the medium; (3)the response occurred because of a variety of external variations. The movement in 2001 shows that the Daixian county and its adjacent area might be the boundary segment for the relative differential activity. More attention should be paid here.展开更多
In this paper,according to the geological structure and the data on seismicity in the Shanxi seismic belt,the tectonic stress field of this belt is numerically imitated by using the finite element method,and by analyz...In this paper,according to the geological structure and the data on seismicity in the Shanxi seismic belt,the tectonic stress field of this belt is numerically imitated by using the finite element method,and by analyzing synthetically the characteristics of seismogeoiogical structure,seismicity and tectonic stress field,the trend of the coming macroseism in the Shanxi seismic belt can be roughly assessed.The main estimate is as follows.From 1993 to 2015,a strong earthquake with Ms=6.2±0.4 may occur in the Shanxi seismic belt,and there are 3 possible locations for earthquake occurrence,if we arrange according to the order of possibility of earthquake occurrence,the location of a coming earthquake would be(1)the region between Huoxian and Hongdong;(2)the region surrounded by Datong,Huairen,Yingxian and Hunyuan,and(3)the region surrounded by eastern Lingqiu to both ends of the Laiyuan fault.展开更多
基金The Project (Continental Geodynamics and Continental Earthquakes! (95-13-03-06).
文摘Based on the data from 4 times of repeated measurements (1996-1999) of GPS monitoring network arranged along Shanxi fault zone, the current horizontal movement of Shanxi fault zone and its relationship with Yangyuan-Hunyuan earthquake (M=5.6; 39.8°N, 113.9°E; November 1, 1999) which occurred at the north part of the monitoring network is analyzed. The results from the analysis indicate: (1) The horizontal movement along Shanxi fault zone was not obvious from 1996 to 1997; (2) The intensity of horizontal movement along Shanxi fault zone increased at the period of 1997 to 1998, and there are three areas with relatively higher strain (1×10-6) appeared, i.e., the source region, Xinzhou region and northeastern part of Jiexiu; (3) Although the dominant movement direction of Shanxi fault zone in the period of 1998 to 1999 was consistent with the fault striking direction, but as compared with the movement in the passed year, the direction was almost reversed, while the absolute value of the movement was close each other; (4) The accumulated horizontal movement along Shanxi fault zone from 1996 to 1999 became obvious gradually. It can be divided into three parts by considering its tendency: (a) the dominant direction of movement in north of Xinzhou is NNE (0.8 cm); (b) in south of Quwo it is SSW (1 cm); (c) in the central area it is rather complicated, the deformation in the southern part is little more large, but in the view of whole area there is no dominant movement exist. Generally speaking, Shanxi fault zone is mainly controlled by the NNE-SSW-trending extension stress field, but there is no strike-slip movement. In the period of 1997 to 1998, there might be a clear stress disturb and it was essentially recovered in 1999. Then the Yangyuan-Hunyuan earthquake occurred. Very possible, this disturb is the triggering to the earthquake.
文摘This paper makes a systematical study on characteristics of structure and motion of the tectonic blocks in northern part of the Shanxi fault depression zone by means of geometrical and kinematical analysis of the blocks. The ki-netic behavior of the blocks is discussed by comparing associated geomorphic features of fault movement. All analyses and studies are based on a Domino model. The block movement, fault basin extension and their regional distribution are systematically investigated. The result shows: (a) The studied region is divided into sub-regions by NW striking faults: the western, middle and eastern sub-region with crustal extension being 4.46 km, 2.80 km and 1.86 km, respectively. The extensional amount of each block in the region is estimated being generally about 1 km. The calculated result using the block motion model approximately fits the data of geologic survey. (b) Block kin-ematical features are obviously different between the northern and southern part, with the Hengshan block in be-tween, of the studied region. Moreover, the magnitude of the largest historical earthquake in the northern part is about 6, while that in the southern is 7. The faulted blocks in the northern sub-region show northwestward exten-sion, indicating a feature of extensional graben, while the blocks in the southern part manifest tilt motion, extend-ing southeastward, in the opposite sense of fault dipping. Additional tectonic stress generated by block rotation may be one of major factors affecting seismogenic process in the region. It is responsible for the difference in the movement of the block boundary faults and seismic activities between the two sub-regions.
基金supported by Open Grant from State key Laboratory of Geodesy and Earth’s Dynamics (Grant No. SKLGED2014-4-4-E)Office of Science and Technology in Shanxi province based on research Projects (2012011029)+1 种基金Scientific and Technological Research Projects in Shanxi province (20100311129-2, 20090311084)the China Earthquake Administration spark Project (XH15007)
文摘The Shanxi rift zone is one of the largest and active Cenozoic grabens in the world, studying the velocity structure of the crust and upper mantle in this region may help us to understand the mechanisms of rift processes and the seismogenic environment of active seismicity in continental rifts. In this work, using the broadband seismic data of Shanxi, Hebei, Henan, Shaanxi provinces, and the Inner Mongolia Autonomous Region from February 2009 to November 2011, we have picked out 350 high-quality phase velocity dispersion curves of fundamental mode Rayleigh waves at periods from 8 to 75 s, and Rayleigh wave phase velocity maps have been constructed from 8 to 75 s period with horizontal resolution ranging from 40 to 50 km by two-station surface-wave tomography. Then, using a genetic algorithm, a 3D shear-wave speed model of the crust and uppermost mantle have been derived from these maps with a spatial resolution of 0.4° × 0.4°. Four characteristics can be outlined from the results： （1） Except in the Datong volcanic zone, in the depth range of 11-30 km, the location of a transition zone between the highand low-velocity regions is in agreement with the seismicity pattern in the study region, and the earthquakes are mostly concentrated near this transition zone; （2） In the depth range of 31-40 km, shear-wave velocities are higher to the south of the Taiyuan Basin and lower to the north, which is similar to the distribution pattern of Moho depth variations in the Shanxi region; （3） The shear-wave velocity pattern of higher velocities to the south of 38×N and lower velocities to the north is found to be consistent with that from the upper crustal levels to depth of 70 km. At the deeper depths, the spatial scale of the low-velocity anomalies zone in the north is gradually shrinking with depth increasing, the low-velocity anomalies are gradually disappearing beneath the Datong volcanic zone at the depth of 151-200 km. We proposed that the root of the Datong volcano may reach to a depth around 150 km; （4） Along the N-S vertical profile at 112.8°E, the 38°N latitude is the boundary between high and low velocities, arguing the tectonic difference between the Shanxi rift zone and its flanks, in the rift zone the seismic velocity is dominated by low-velocity anomalies while in the flanks it is high.
文摘The tendency and dynamic characteristics of horizontal movement along the Shanxi fault zone have been analyzed using the data obtained from 6 repeated measurements (1996～2001) in the GPS monitoring network arranged along the Shanxi fault zone. The results indicate: (1) the tendentious activity of the present stage is characterized by a W trending movement along the northern segment of the zone, an E trending movement along the southern segment and counter clockwise differential activity on the whole, but the intensity of the tendentious activity is not high. The tendentious differential movement is only about 3 mm/a in the direction perpendicular to the fault zone from the south to the north, and its stretch in the SN direction is only 1 mm/a and mainly occurs along the north segment of the fault; (2) The azimuth of the principal compressive stress field reflected by the tendentious movement is 72°; (3) The property of annual activity is not the same, even contrary to one another or deviates from the tendentious activity. Therefore, the parameters of the strain field derived from them dont reflect the physical characteristics of the basic stress field. (4) The high frequency movement (yearly) does not only exist but is also complicated by an intensity several times higher than that of the tendentious movement; (5) Obvious differential movements, including strike slip, can not be seen in either in secular activity or annual activity on both sides of any fault. The tendentious movement not only verifies the conjecture of “strong in the south and weak in north”, which is the basic feature forcing the western boundary of the North China area, but it also extends to the hinterland of North China. The fact that there is no obvious differential activity on both sides of the fault might indicate that the differential activity among the intraplate blocks is completed by gradual variation in a certain space, rather than the abrupt change bordered by a fault or narrow stripe zone. The obvious dynamic activity might indicate: (1) there is stress disturbance in the basic stress field; (2) the inhomogeneous or non synchronous variation that appeared in the regional stress and strain fields was due to the different physical property of the medium; (3)the response occurred because of a variety of external variations. The movement in 2001 shows that the Daixian county and its adjacent area might be the boundary segment for the relative differential activity. More attention should be paid here.
文摘In this paper,according to the geological structure and the data on seismicity in the Shanxi seismic belt,the tectonic stress field of this belt is numerically imitated by using the finite element method,and by analyzing synthetically the characteristics of seismogeoiogical structure,seismicity and tectonic stress field,the trend of the coming macroseism in the Shanxi seismic belt can be roughly assessed.The main estimate is as follows.From 1993 to 2015,a strong earthquake with Ms=6.2±0.4 may occur in the Shanxi seismic belt,and there are 3 possible locations for earthquake occurrence,if we arrange according to the order of possibility of earthquake occurrence,the location of a coming earthquake would be(1)the region between Huoxian and Hongdong;(2)the region surrounded by Datong,Huairen,Yingxian and Hunyuan,and(3)the region surrounded by eastern Lingqiu to both ends of the Laiyuan fault.
