The 26 November 2005 Jiujiang-Ruichang, Jiangxi, Ms 5.7 earthquake occurred in a seismotectonic setting of moderate earthquake. The northwest-trending Xiangfan-Guangji fault （XFG） does not enter into the epicenter v...The 26 November 2005 Jiujiang-Ruichang, Jiangxi, Ms 5.7 earthquake occurred in a seismotectonic setting of moderate earthquake. The northwest-trending Xiangfan-Guangji fault （XFG） does not enter into the epicenter vicinity, but the northeast-trending Ruichang-Wuning fault （RWF） as a regional fault extends to the epicenter nearby, appearing as the Ruichang basin and its marginal faults. Tilting of the Ruichang Basin （RCB） in the Quaternary was controlled by the RCB southeast- marginal, buried fault （RSMBF）. Shallow geophysical survey reveals that the RSMBF caused an offset of the reflection layers. Drill hole columnar section demonstrates that there are about 10-12 m displacement in the lower section of the middle-Pleistocene Series along the RSMBF, but no disruption is found in the upper section of the middle-Pleistocene Series. The RSMBF not only has activity in the Quaternary, but also coincides with the nodal plane I from the focal mechanism of the Jiujiang- Ruichang Ms 5.7 earthquake. This evidence, including aftershock distribution and isoseismic lines, strongly suggests that the RSMBF might be the seismogenic tectonics. The RWF is discontinuous at the surface, and consists of three en echelon Quaternary basins, which are the Ruichang, Fanzhen and Wuning basins. Three moderate earthquakes, the Fanzhen ML 4.9 earthquake, the Yejiapu ML 4.1 earthquake and the Jiujiang-Ruichang Ms 5.7 earthquake, have happened in the basins since 1995. The seismogenic tectonics of the Jiujiang-Ruichang Ms 5.7 earthquake is not isolated, but may be controlled by the RWF at depth, the slip of which causes the accumulation of energy for earthquake occurrence.展开更多
The Kunlun Fault,an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks,is one of the major left lateral strike-slip faults in the Tibetan Plateau.Previous research has not reached a consensus on...The Kunlun Fault,an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks,is one of the major left lateral strike-slip faults in the Tibetan Plateau.Previous research has not reached a consensus on agreeable slip rates along much of its length and the slip rate gradient along the eastern part,both of which play critical roles in a range of models for the eastward extrusion and thickened crust of the Tibetan Plateau.New slip rates have been determined at sites along the eastern part of the Kunlun Fault by dating deposits and measuring atop displaced fluvial terrace risers.Field investigations and interpretation of satellite images reveal geometrical features of the fault and the late Quaternary offset,new earthquake ruptures and surface-rupturing segmentation,from which long-term slip rates and earthquake recurrence intervals on the fault are estimated.The tectonic geomorphology method has determined that the long-term horizontal slip rates on the Tuosuohu,Maqin and Maqu segments from west to east are 11.2±1,9.3±2,and 4.9±1.3 mm/a while their vertical slip rates are 1.2±0.2,0.7±0.1,and 0.3 mm/a in the late Quaternary.Results indicate that the slip rates regularly decrease along the eastern ～300 km of the fault from >10 to <5 mm/a.This is consistent with the decrease in the gradient such that at the slip rate break point is at the triple point intersection with the transverse fault,which in turn is transformed to the Awancang Fault.The vector decomposition for this tectonic transformation shows that the western and eastern branches of the Awancang Fault fit the slip-partitioning mode.The slip rate of the southwestern wall is 4.6 mm/a relative to the northeastern wall and the slip direction is 112.1°.The mid-eastern part of the Kunlun Fault can be divided into three independent segments by the A'nyêmaqên double restraining bend and the Xigongzhou intersection zone,which compose the surface rupture segmentation indicators for themselves as well as the ending point of the 1937 M7.5 Tuosuohu earthquake.The average recurrence interval of the characteristic earthquakes are estimated to be 500-1000 a,respectively.The latest earthquake ruptures occurred in AD 1937 on the western Tuosuohu segment,as compared to ～514-534 a BP on the Maqin segment,and ～1055 to 1524 a BP on the Maqu segment.This may indicate a unidirectional migration for surface rupturing earthquakes along the mid-eastern Kunlun Fault related to stress triggered between these segments.Meanwhile,the long-term slip rate is obtained through the single event offset and the recurrence interval,which turn out to be the same results as those determined by the offset tectonic geomorphology method,i.e.,the decreasing gradient corresponds to the geometrical bending and the fault's intersection with the transverse fault.Therefore,the falling slip rate gradient of the mid-eastern Kunlun Fault is mainly caused by eastward extension of the fault and its intersection with the transverse fault.展开更多
The apparent ages of samples are obtained from fission track dating of apatite samples collected from the fault zones in Mabian area, southern Sichuan Province. In addition, thermal history is simulated from the obtai...The apparent ages of samples are obtained from fission track dating of apatite samples collected from the fault zones in Mabian area, southern Sichuan Province. In addition, thermal history is simulated from the obtained data by applying AFT Solve Program, to acquire the thermal evolution history of the samples. The result shows that tectonically the Mabian area was relatively stable between 25 and 3 Ma, compared to the inner parts and other marginal areas of the Tibetan Plateau. The studied area had little response to the rapid uplift events that occurred for several times in the Tibetan Plateau during 25-3 Ma. The latest thermal event related to the activity of the Lidian fault zone (about 8 Ma ) is later than that of the Ebian fault zone (18-15 Ma ) to the west, indicating to some extent that the evolution of fault activity in the Mabian area has migrated from west to east. The latest extensive tectonic uplift occurred since about 3 Ma. As compared with the Xianshuihe fault zone, the Mabian area is closer to the east- ern margin of the plateau, while the time of fast cooling event in this area is later than that in the southeast segment of the Xianshuihe fault zone (3.6-3.46 Ma ). It appears to support the assumption of episodic uplift and stepwise outward extension of the eastern boundary of the Tibetan Plateau in late Cenozoic.展开更多
The MS6.4 Menyuan earthquake occurred on the northern side of the Lenglongling fault(LLLF) in the mid-western of the Qilian-Haiyuan fault zone on January 21, 2016. The earthquake epicenter was distant from the Minle-D...The MS6.4 Menyuan earthquake occurred on the northern side of the Lenglongling fault(LLLF) in the mid-western of the Qilian-Haiyuan fault zone on January 21, 2016. The earthquake epicenter was distant from the Minle-Damaying and Huangcheng-Shuangta faults, eastern of the Northern Qilian Shan fault zone. A near northwest-striking rupture plane intersects the two faults at a certain angle. The focal mechanism solution shows that this was a thrust-type earthquake, slightly different from the strike-slip movement with a thrust component of the LLLF. Field geological mapping, tectonic geomorphology analysis, trench excavation and 14 C dating reveal that(1) the LLLF has been obviously active since the Holocene, and may behave with characteristic slip behavior and produce M_W7.3–7.5 earthquakes;(2) the LLLF appears as a flower structure in terms of structure style, and dips NNE at a steep angle; and(3) the most recent earthquake event occurred after 1815–1065 a BP. An associated fault, the Northern Lenglongling fault(NLLLF), is located at the northwestern end of the LLLF. Consequently, the NLLLF was continually subject to tectonic pushing effects from the left-lateral shear at the end of the LLLF, and, accordingly, it bent and rotated outward tectonically.Subsequently, the fault deviated from the dominant rupture azimuth and activity weakened. In the late Quaternary, it behaved as a thrust fault with no obvious deformation at the surface. This is indicated by the arc shape, with a micro-protrusion northeastward,and no geologic or geomorphic signs of surface rupturing since the late Quaternary. However, such faults could still rupture at depth, producing moderate-strong earthquakes. The geometric and kinematic properties of the NLLLF are in good agreement with the occurrence and kinematic properties of nodal plane 2, and with the distribution characteristics of the aftershocks and seismic intensity. Therefore, the NLLLF is a more suitable seismogenic structure for the MS 6.4 Menyuan earthquake. In addition, the thrust movement of the NLLLF accommodates subsequent movement of the LLLF. During the historical evolution of the NLLLF,the LLLF and the NLLLF have affected the local topography through tectonic uplift.展开更多
文摘The 26 November 2005 Jiujiang-Ruichang, Jiangxi, Ms 5.7 earthquake occurred in a seismotectonic setting of moderate earthquake. The northwest-trending Xiangfan-Guangji fault （XFG） does not enter into the epicenter vicinity, but the northeast-trending Ruichang-Wuning fault （RWF） as a regional fault extends to the epicenter nearby, appearing as the Ruichang basin and its marginal faults. Tilting of the Ruichang Basin （RCB） in the Quaternary was controlled by the RCB southeast- marginal, buried fault （RSMBF）. Shallow geophysical survey reveals that the RSMBF caused an offset of the reflection layers. Drill hole columnar section demonstrates that there are about 10-12 m displacement in the lower section of the middle-Pleistocene Series along the RSMBF, but no disruption is found in the upper section of the middle-Pleistocene Series. The RSMBF not only has activity in the Quaternary, but also coincides with the nodal plane I from the focal mechanism of the Jiujiang- Ruichang Ms 5.7 earthquake. This evidence, including aftershock distribution and isoseismic lines, strongly suggests that the RSMBF might be the seismogenic tectonics. The RWF is discontinuous at the surface, and consists of three en echelon Quaternary basins, which are the Ruichang, Fanzhen and Wuning basins. Three moderate earthquakes, the Fanzhen ML 4.9 earthquake, the Yejiapu ML 4.1 earthquake and the Jiujiang-Ruichang Ms 5.7 earthquake, have happened in the basins since 1995. The seismogenic tectonics of the Jiujiang-Ruichang Ms 5.7 earthquake is not isolated, but may be controlled by the RWF at depth, the slip of which causes the accumulation of energy for earthquake occurrence.
基金supported by National Natural Science Foundation of China (Grant Nos. 40821160550 and 40974057)International Scientific Joint Project of China (Grant No. 2009DFA21280)
文摘The Kunlun Fault,an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks,is one of the major left lateral strike-slip faults in the Tibetan Plateau.Previous research has not reached a consensus on agreeable slip rates along much of its length and the slip rate gradient along the eastern part,both of which play critical roles in a range of models for the eastward extrusion and thickened crust of the Tibetan Plateau.New slip rates have been determined at sites along the eastern part of the Kunlun Fault by dating deposits and measuring atop displaced fluvial terrace risers.Field investigations and interpretation of satellite images reveal geometrical features of the fault and the late Quaternary offset,new earthquake ruptures and surface-rupturing segmentation,from which long-term slip rates and earthquake recurrence intervals on the fault are estimated.The tectonic geomorphology method has determined that the long-term horizontal slip rates on the Tuosuohu,Maqin and Maqu segments from west to east are 11.2±1,9.3±2,and 4.9±1.3 mm/a while their vertical slip rates are 1.2±0.2,0.7±0.1,and 0.3 mm/a in the late Quaternary.Results indicate that the slip rates regularly decrease along the eastern ～300 km of the fault from >10 to <5 mm/a.This is consistent with the decrease in the gradient such that at the slip rate break point is at the triple point intersection with the transverse fault,which in turn is transformed to the Awancang Fault.The vector decomposition for this tectonic transformation shows that the western and eastern branches of the Awancang Fault fit the slip-partitioning mode.The slip rate of the southwestern wall is 4.6 mm/a relative to the northeastern wall and the slip direction is 112.1°.The mid-eastern part of the Kunlun Fault can be divided into three independent segments by the A'nyêmaqên double restraining bend and the Xigongzhou intersection zone,which compose the surface rupture segmentation indicators for themselves as well as the ending point of the 1937 M7.5 Tuosuohu earthquake.The average recurrence interval of the characteristic earthquakes are estimated to be 500-1000 a,respectively.The latest earthquake ruptures occurred in AD 1937 on the western Tuosuohu segment,as compared to ～514-534 a BP on the Maqin segment,and ～1055 to 1524 a BP on the Maqu segment.This may indicate a unidirectional migration for surface rupturing earthquakes along the mid-eastern Kunlun Fault related to stress triggered between these segments.Meanwhile,the long-term slip rate is obtained through the single event offset and the recurrence interval,which turn out to be the same results as those determined by the offset tectonic geomorphology method,i.e.,the decreasing gradient corresponds to the geometrical bending and the fault's intersection with the transverse fault.Therefore,the falling slip rate gradient of the mid-eastern Kunlun Fault is mainly caused by eastward extension of the fault and its intersection with the transverse fault.
基金the National Basic Research Program of China (No.2004CB418401)
文摘The apparent ages of samples are obtained from fission track dating of apatite samples collected from the fault zones in Mabian area, southern Sichuan Province. In addition, thermal history is simulated from the obtained data by applying AFT Solve Program, to acquire the thermal evolution history of the samples. The result shows that tectonically the Mabian area was relatively stable between 25 and 3 Ma, compared to the inner parts and other marginal areas of the Tibetan Plateau. The studied area had little response to the rapid uplift events that occurred for several times in the Tibetan Plateau during 25-3 Ma. The latest thermal event related to the activity of the Lidian fault zone (about 8 Ma ) is later than that of the Ebian fault zone (18-15 Ma ) to the west, indicating to some extent that the evolution of fault activity in the Mabian area has migrated from west to east. The latest extensive tectonic uplift occurred since about 3 Ma. As compared with the Xianshuihe fault zone, the Mabian area is closer to the east- ern margin of the plateau, while the time of fast cooling event in this area is later than that in the southeast segment of the Xianshuihe fault zone (3.6-3.46 Ma ). It appears to support the assumption of episodic uplift and stepwise outward extension of the eastern boundary of the Tibetan Plateau in late Cenozoic.
基金supported by a Special Project on Earthquake Research, the China Active Fault Survey Project-The South-North Seismic Zone Northern Segment (Grant No. 201408023)Fundamental Research Funds in Institute of Crustal Dynamics, China Earthquake Administration (Grant No. ZDJ2015-16)
文摘The MS6.4 Menyuan earthquake occurred on the northern side of the Lenglongling fault(LLLF) in the mid-western of the Qilian-Haiyuan fault zone on January 21, 2016. The earthquake epicenter was distant from the Minle-Damaying and Huangcheng-Shuangta faults, eastern of the Northern Qilian Shan fault zone. A near northwest-striking rupture plane intersects the two faults at a certain angle. The focal mechanism solution shows that this was a thrust-type earthquake, slightly different from the strike-slip movement with a thrust component of the LLLF. Field geological mapping, tectonic geomorphology analysis, trench excavation and 14 C dating reveal that(1) the LLLF has been obviously active since the Holocene, and may behave with characteristic slip behavior and produce M_W7.3–7.5 earthquakes;(2) the LLLF appears as a flower structure in terms of structure style, and dips NNE at a steep angle; and(3) the most recent earthquake event occurred after 1815–1065 a BP. An associated fault, the Northern Lenglongling fault(NLLLF), is located at the northwestern end of the LLLF. Consequently, the NLLLF was continually subject to tectonic pushing effects from the left-lateral shear at the end of the LLLF, and, accordingly, it bent and rotated outward tectonically.Subsequently, the fault deviated from the dominant rupture azimuth and activity weakened. In the late Quaternary, it behaved as a thrust fault with no obvious deformation at the surface. This is indicated by the arc shape, with a micro-protrusion northeastward,and no geologic or geomorphic signs of surface rupturing since the late Quaternary. However, such faults could still rupture at depth, producing moderate-strong earthquakes. The geometric and kinematic properties of the NLLLF are in good agreement with the occurrence and kinematic properties of nodal plane 2, and with the distribution characteristics of the aftershocks and seismic intensity. Therefore, the NLLLF is a more suitable seismogenic structure for the MS 6.4 Menyuan earthquake. In addition, the thrust movement of the NLLLF accommodates subsequent movement of the LLLF. During the historical evolution of the NLLLF,the LLLF and the NLLLF have affected the local topography through tectonic uplift.
