Based on the concept of "active blocks" and spatial distribution of historical earthquakes with surface ruptures as well as major and subordinate active faults. The Sichuan-Yunnan region can be divided into ...Based on the concept of "active blocks" and spatial distribution of historical earthquakes with surface ruptures as well as major and subordinate active faults. The Sichuan-Yunnan region can be divided into four first-order blocks. They are the Markam block (I), the Sichuan-Yunnan rhombic block (II), Baoshan-Pu'er block (III), and Mizhina-Ximeng block (IV). Cut by sub-ordinate NE-trending active faults, the Sichuan-Yunnan rhombic block (II) can be further divided into two sub-blocks: the northwestern Sichuan sub-block (II1) and the middle Yunnan sub-block (II2), while the Baoshan- Pu'er block (III) can be further divided into three sub-blocks: Baoshan sub-block (III1), Jinggu sub-block (III2), and Mengla sub-block (III3). A quantitative study of offset landforms is carried out and the basic types of active faults and their long-term slip rates along the major boundaries of active blocks of different orders in the Sichuan-Yunnan region are determined, through slip vector analysis, the motion states of the active blocks are clarified and the deformation coordination on the block margins is discussed. It is suggested that the tectonic motion of the blocks in this region is a complex or superimposition of three basic types of motions: southeastward sliding, rotating on vertical axis, and uplifting. The Markam block (I), the northwestern Sichuan sub-block (II1), and middle Yunnan sub-block (II2) have a southeastward horizontal sliding rate of 1-5 mm/a, clockwise rotating angular rate of 1.4-4(/Ma, and uplifting rate of about 1 mm/a. The Baoshan-Pu'er (III) and Mizhina-Ximeng (IV) blocks have also been extensively clockwise rotated. This pattern of motion is a strain response to the collision between the Indian and Eurasian plates and the localized deformation and differential slip on the block margins associated with the northward motion of the Indian Plate. Because a set of transverse thrusts between the blocks absorbs and transforms some components of eastward or southeastward sliding motion, the eastward escape or 展开更多
We used 71670 P-wave arrival times from 3594 earthquakes recorded by the Sichuan and Yunnan seismic networks to determine the three-dimensional P-wave velocity structure in the crust and uppermost mantle beneath the s...We used 71670 P-wave arrival times from 3594 earthquakes recorded by the Sichuan and Yunnan seismic networks to determine the three-dimensional P-wave velocity structure in the crust and uppermost mantle beneath the southeastern Tibetan Plateau. Our results show that prominent low P-wave velocity (low-Vp) anomalies exist in the midto lower crust of the Song- pan-Ganze and Sichuan-Yunnan blocks. In contrast, a high P-wave velocity (high-Vp) anomaly is resolved in the middle and lower crust beneath the Sichuan Basin. Our tomographic results provide seismic evidence for a dynamic model of lower crustal flow. Ongoing lower crustal flow beneath the central and eastern Tibetan Plateau abuts against the mechanically strong Si- chuan Basin resulting in accumulated strain in the Longmen Shan region. When a critical accumulation of strain energy was reached, its sudden release led to the occurrence of 2008 Wenchuan earthquake. Pronounced low-Vp anomalies are observed in the uppermost mantle in the region south of ~26°N. Combining these results with shear-wave splitting investigations, we suggest that the flow of asthenospheric material has impacted the velocity structure of the uppermost mantle and caused the thinning of the southwestern Yangtze Craton.展开更多
Based on the existing materials of fault segmentation,characteristic earthquakes,and their empirical relationships,we calculated the parameters of the fault segments,such as length,width,magnitudes of characteristic e...Based on the existing materials of fault segmentation,characteristic earthquakes,and their empirical relationships,we calculated the parameters of the fault segments,such as length,width,magnitudes of characteristic earthquakes,etc.Constrained by GPS velocity field,the slip rates of these fault segments in depth were inversed using the 3-D half-space elastic dislocation model.As not all of the recurrence periods and co-seismic displacements of characteristic earthquakes are known,we selected the fault segments with these two parameters known and calculated the accumulation rate of average co-seismic displacement,which shows the faults' slip rate in seismogenic layer.Then,the slip rate in depth was compared with that in seismogenic layer,the relationship between them was obtained,and this relationship was used to get the recurrence periods and co-seismic displacements of all fault segments.After the studies above,we calculated the co-seismic deformation field of all the earthquakes larger than M s 6.8 from AD 1700 one by one and inversed the potential displacement in the co-seismic deformation field.Then,we divided the potential displacement by the slip rate from GPS inversion to get the influences of these fault segments,added the influences into the elapsed time of the characteristic earthquakes,and obtained the earthquake hazard degree of all the segments we studied in the form of the ratio of elapsed time to recurrence period;so,we name the ratio as the Impending Earthquake Risk (IER).Historical earthquake cases show that the fault segment is in safety when the IER is less than 1 but in danger after the IER becomes larger than 1.In 2009,the IER is larger than 1 on the following segments,1.35 on the Tagong segment of Xianshuihe fault,1 on the Menggu-Dongchuan segment,1.04 on the Dongchuan-Xundian segment,and 1.09 on the Yiliang-Chengjiang segment of Xiaojiang fault.展开更多
鲜水河-小江左旋走滑断裂系是调节青藏高原东南部物质向东南挤出的大型边界断裂。云南巧家断裂作为小江断裂带北段,其晚第四纪走滑速率是认识川滇地块东部边界应变调节方式的关键。本文利用无人机航摄和地面激光扫描技术,获取了该断裂...鲜水河-小江左旋走滑断裂系是调节青藏高原东南部物质向东南挤出的大型边界断裂。云南巧家断裂作为小江断裂带北段,其晚第四纪走滑速率是认识川滇地块东部边界应变调节方式的关键。本文利用无人机航摄和地面激光扫描技术,获取了该断裂段穿过金沙江河谷区红路和蒙姑两处的高分辨率地形数据,恢复出断层错动T2和T3两期阶地陡坎上缘的左旋位错量分别为120±5~128±1 m和193±1~202±1 m。根据T3中次生碳酸盐的AMS-14C法测年结果,结合已有的类似阶地年龄数据,并经气候曲线校正后认为,区域上T2和T3被废弃应分别发生在冰后期和末次盛冰期末期,时间为8.5~11.2 ka BP和18.6~21.4 ka BP。据此估算,小江断裂带巧家段的晚第四纪平均走滑速率为10~13 mm/a。进一步统计分析小江断裂带的晚第四纪走滑速率,发现巧家至宜良以北的段落,总体保持着10~15 mm/a的高走滑速率。但从宜良向南,断裂走滑速率出现了分段递减的特征,至建水以南快速减小到中-北段的近十分之一。小江断裂带中-北段的高走滑速率以及向南的分段式递减现象,反映在宜良以北,小江断裂带的走滑剪切作用是调节川滇地块向东南旋转-挤出运动的主要方式,但向南伴随变形分解作用,调节方式转变为了伸展、旋转和逆冲等多种方式共存的复杂形式。因此,进一步精细化定量限定川滇地块东部边界断裂的应变分解作用,是深入认识青藏高原物质挤出方式及其机制的关键。展开更多
The Xiaojiang fault is a major active left-lateral fault along the southeastern margin of the Tibetan Plateau.The largest historical earthquake in Yunnan Province, with a magnitude 8 and a mean coseismic left-lateral ...The Xiaojiang fault is a major active left-lateral fault along the southeastern margin of the Tibetan Plateau.The largest historical earthquake in Yunnan Province, with a magnitude 8 and a mean coseismic left-lateral displacement of ~ 6.9 m, occurred on the western branch of the Xiaojiang fault.Studying this fault is important in understanding current deformation and kinematic characteristics of the Tibetan Plateau.Activities and stretches have been well undertaken on the Xiaojiang fault, while paleoseismic research work is always the weak link on this fault.To investigate the paleoseismic history and large earthquake activity of the Xiaojiang fault, we opened a large trench at the northern edge of Caohaizi sag pond on the western branch of the Xiaojiang fault.Six paleoseismic events have been identified, and named E1 through E6 from the oldest to the youngest.Charcoal and woods are abundant, 20 samples were dated to constrain the ages of the paleoseismic events at 40 000–36 300 BC, 35 400–24 800 BC, 9 500 BC–AD 500, AD 390–720, AD 1120–1620 and AD 1750–present.We associate the youngest event E6 with the 1833 M8 earthquake.Events E4, E5 and E6 show a continuous record of the western strand of the Xiaojiang fault in the late Holocene, with a average recurrence interval of 370–480 yr.Large earthquake recurrence in the late Holocene is far less than the recurrence of 2000–4000 yr posed in previous studies.Thus, the seismic hazard on the Xiaojiang fault should be reevaluated.Furthermore, the irregular recurrence of large earthquakes on the Xiaojiang fault and other faults in the Xianshuihe-Xiaojiang system, indicates the uneven southeastward extrusion of the Sichuan-Yunnan block along the southeastern margin of the Tibetan Plateau.展开更多
文摘Based on the concept of "active blocks" and spatial distribution of historical earthquakes with surface ruptures as well as major and subordinate active faults. The Sichuan-Yunnan region can be divided into four first-order blocks. They are the Markam block (I), the Sichuan-Yunnan rhombic block (II), Baoshan-Pu'er block (III), and Mizhina-Ximeng block (IV). Cut by sub-ordinate NE-trending active faults, the Sichuan-Yunnan rhombic block (II) can be further divided into two sub-blocks: the northwestern Sichuan sub-block (II1) and the middle Yunnan sub-block (II2), while the Baoshan- Pu'er block (III) can be further divided into three sub-blocks: Baoshan sub-block (III1), Jinggu sub-block (III2), and Mengla sub-block (III3). A quantitative study of offset landforms is carried out and the basic types of active faults and their long-term slip rates along the major boundaries of active blocks of different orders in the Sichuan-Yunnan region are determined, through slip vector analysis, the motion states of the active blocks are clarified and the deformation coordination on the block margins is discussed. It is suggested that the tectonic motion of the blocks in this region is a complex or superimposition of three basic types of motions: southeastward sliding, rotating on vertical axis, and uplifting. The Markam block (I), the northwestern Sichuan sub-block (II1), and middle Yunnan sub-block (II2) have a southeastward horizontal sliding rate of 1-5 mm/a, clockwise rotating angular rate of 1.4-4(/Ma, and uplifting rate of about 1 mm/a. The Baoshan-Pu'er (III) and Mizhina-Ximeng (IV) blocks have also been extensively clockwise rotated. This pattern of motion is a strain response to the collision between the Indian and Eurasian plates and the localized deformation and differential slip on the block margins associated with the northward motion of the Indian Plate. Because a set of transverse thrusts between the blocks absorbs and transforms some components of eastward or southeastward sliding motion, the eastward escape or
基金supported by Chinese Academy of Sciences (Grant No. KZCZ-YW-134)National Natural Science Foundation of China (Grant No. 90814014)
文摘We used 71670 P-wave arrival times from 3594 earthquakes recorded by the Sichuan and Yunnan seismic networks to determine the three-dimensional P-wave velocity structure in the crust and uppermost mantle beneath the southeastern Tibetan Plateau. Our results show that prominent low P-wave velocity (low-Vp) anomalies exist in the midto lower crust of the Song- pan-Ganze and Sichuan-Yunnan blocks. In contrast, a high P-wave velocity (high-Vp) anomaly is resolved in the middle and lower crust beneath the Sichuan Basin. Our tomographic results provide seismic evidence for a dynamic model of lower crustal flow. Ongoing lower crustal flow beneath the central and eastern Tibetan Plateau abuts against the mechanically strong Si- chuan Basin resulting in accumulated strain in the Longmen Shan region. When a critical accumulation of strain energy was reached, its sudden release led to the occurrence of 2008 Wenchuan earthquake. Pronounced low-Vp anomalies are observed in the uppermost mantle in the region south of ~26°N. Combining these results with shear-wave splitting investigations, we suggest that the flow of asthenospheric material has impacted the velocity structure of the uppermost mantle and caused the thinning of the southwestern Yangtze Craton.
基金supported by the National Basic Research Program of China (Grant No. 2008CB425704)the Open Foundation of State Key Laboratory of Earthquake Dynamics (Grant No. LED2009B02)
文摘Based on the existing materials of fault segmentation,characteristic earthquakes,and their empirical relationships,we calculated the parameters of the fault segments,such as length,width,magnitudes of characteristic earthquakes,etc.Constrained by GPS velocity field,the slip rates of these fault segments in depth were inversed using the 3-D half-space elastic dislocation model.As not all of the recurrence periods and co-seismic displacements of characteristic earthquakes are known,we selected the fault segments with these two parameters known and calculated the accumulation rate of average co-seismic displacement,which shows the faults' slip rate in seismogenic layer.Then,the slip rate in depth was compared with that in seismogenic layer,the relationship between them was obtained,and this relationship was used to get the recurrence periods and co-seismic displacements of all fault segments.After the studies above,we calculated the co-seismic deformation field of all the earthquakes larger than M s 6.8 from AD 1700 one by one and inversed the potential displacement in the co-seismic deformation field.Then,we divided the potential displacement by the slip rate from GPS inversion to get the influences of these fault segments,added the influences into the elapsed time of the characteristic earthquakes,and obtained the earthquake hazard degree of all the segments we studied in the form of the ratio of elapsed time to recurrence period;so,we name the ratio as the Impending Earthquake Risk (IER).Historical earthquake cases show that the fault segment is in safety when the IER is less than 1 but in danger after the IER becomes larger than 1.In 2009,the IER is larger than 1 on the following segments,1.35 on the Tagong segment of Xianshuihe fault,1 on the Menggu-Dongchuan segment,1.04 on the Dongchuan-Xundian segment,and 1.09 on the Yiliang-Chengjiang segment of Xiaojiang fault.
文摘鲜水河-小江左旋走滑断裂系是调节青藏高原东南部物质向东南挤出的大型边界断裂。云南巧家断裂作为小江断裂带北段,其晚第四纪走滑速率是认识川滇地块东部边界应变调节方式的关键。本文利用无人机航摄和地面激光扫描技术,获取了该断裂段穿过金沙江河谷区红路和蒙姑两处的高分辨率地形数据,恢复出断层错动T2和T3两期阶地陡坎上缘的左旋位错量分别为120±5~128±1 m和193±1~202±1 m。根据T3中次生碳酸盐的AMS-14C法测年结果,结合已有的类似阶地年龄数据,并经气候曲线校正后认为,区域上T2和T3被废弃应分别发生在冰后期和末次盛冰期末期,时间为8.5~11.2 ka BP和18.6~21.4 ka BP。据此估算,小江断裂带巧家段的晚第四纪平均走滑速率为10~13 mm/a。进一步统计分析小江断裂带的晚第四纪走滑速率,发现巧家至宜良以北的段落,总体保持着10~15 mm/a的高走滑速率。但从宜良向南,断裂走滑速率出现了分段递减的特征,至建水以南快速减小到中-北段的近十分之一。小江断裂带中-北段的高走滑速率以及向南的分段式递减现象,反映在宜良以北,小江断裂带的走滑剪切作用是调节川滇地块向东南旋转-挤出运动的主要方式,但向南伴随变形分解作用,调节方式转变为了伸展、旋转和逆冲等多种方式共存的复杂形式。因此,进一步精细化定量限定川滇地块东部边界断裂的应变分解作用,是深入认识青藏高原物质挤出方式及其机制的关键。
基金funded by Natural Science Foundation of China (41372218)Special Foundation of the China Earthquake Administration (Grant No.201108001)+2 种基金Science for Earthquake Resilience of China Earthquake Administration (CEA) (XH13021)Special Projects for Basic Research Work of the Institute of Geology, CEA (IGCEA1418)the program of International S&T Cooperation, Ministry of Science and Technology of China (2015DFA21260)
文摘The Xiaojiang fault is a major active left-lateral fault along the southeastern margin of the Tibetan Plateau.The largest historical earthquake in Yunnan Province, with a magnitude 8 and a mean coseismic left-lateral displacement of ~ 6.9 m, occurred on the western branch of the Xiaojiang fault.Studying this fault is important in understanding current deformation and kinematic characteristics of the Tibetan Plateau.Activities and stretches have been well undertaken on the Xiaojiang fault, while paleoseismic research work is always the weak link on this fault.To investigate the paleoseismic history and large earthquake activity of the Xiaojiang fault, we opened a large trench at the northern edge of Caohaizi sag pond on the western branch of the Xiaojiang fault.Six paleoseismic events have been identified, and named E1 through E6 from the oldest to the youngest.Charcoal and woods are abundant, 20 samples were dated to constrain the ages of the paleoseismic events at 40 000–36 300 BC, 35 400–24 800 BC, 9 500 BC–AD 500, AD 390–720, AD 1120–1620 and AD 1750–present.We associate the youngest event E6 with the 1833 M8 earthquake.Events E4, E5 and E6 show a continuous record of the western strand of the Xiaojiang fault in the late Holocene, with a average recurrence interval of 370–480 yr.Large earthquake recurrence in the late Holocene is far less than the recurrence of 2000–4000 yr posed in previous studies.Thus, the seismic hazard on the Xiaojiang fault should be reevaluated.Furthermore, the irregular recurrence of large earthquakes on the Xiaojiang fault and other faults in the Xianshuihe-Xiaojiang system, indicates the uneven southeastward extrusion of the Sichuan-Yunnan block along the southeastern margin of the Tibetan Plateau.
