The 1515 M7/4 Yongsheng earthquake is the strongest earthquake historically in northwest Yunnan.However,its time,magnitude and the seismogenic fault have long been a topic of dispute.In order to accurately define thos...The 1515 M7/4 Yongsheng earthquake is the strongest earthquake historically in northwest Yunnan.However,its time,magnitude and the seismogenic fault have long been a topic of dispute.In order to accurately define those problems,a 1:50000 active tectonic mapping was carried out along the northern segment of the Chenghai-Binchuan fault zone.The result shows that there is an at least 25 km-long surface rupture and a series of seismic landslides distributed along the Jinguan fault and the Chenghai fault.Radiocarbon dating of the 14C samples indicates that the surface rupture should be a part of the deformation zone caused by the Yongsheng earthquake in the year 1515.The distribution characteristics of this surface rupture indicate that the macroscopic epicenter of the 1515 Yongsheng earthquake may be located near Hongshiya,and the seismogenic fault of this earthquake is the Jinguan-Chenghai fault,the northern part of the Chenghai-Binchuan fault zone.Striations on the surface rupture show that the latest motion of the fault is normal faulting.The maximum co-seismic vertical displacement can be 3.8 m,according to the empirical formula for the fault displacement and moment magnitude relationship,the moment magnitude of the Yongsheng earthquake was Mw 7.3-7.4.Furthermore,combining published age data with the 14C data in this paper reveals that at least four large earthquakes of similar size to the 1515 Yongsheng earthquake,have taken place across the northern segment of the Chenghai-Binchuan fault zone since 17190~50 yr.BP.The in-situ recurrence interval of Mw 7.3-7.4 characteristic earthquakes in Yongsheng along this fault zone is possibly on the order of 6 ka.展开更多
The north trending rifts in southern Xizang represent the E-W extension of the plateau and confirming the initial rifting age is key to the study of mechanics of these rifts.Pagri-Duoqing Co graben is located at south...The north trending rifts in southern Xizang represent the E-W extension of the plateau and confirming the initial rifting age is key to the study of mechanics of these rifts.Pagri-Duoqing Co graben is located at southern end of Yadong-Gulu rift,where the late Cenozoic sediments is predominately composed of fluvio-lacustrine and moraine.Based on the sedimentary composition and structures,the fluviolacustrine could be divided into three facies,namely,lacustrine,lacustrine fan delta and alluvial fan.The presence of paleo-currents and conglomerate components and the provenance of the strata around the graben indicate that it was Tethys Himalaya and High Himalaya.Electron spin resonance(ESR)dating and paleo-magnetic dating suggest that the age of the strata ranges from ca.1.2 Ma to ca.8 Ma.Optically stimulated luminescence(OSL)dating showed that moraine in the graben mainly developed from around181-109 ka(late Middle Pleistocene).Combining previous data about the Late Cenozoic strata in other basins,it is suggested that 8-15 Ma may be the initial rifting time.Together with sediment distribution and drainage system,the sedimentary evolution of Pagri could be divided into four stages.The graben rifted at around 15-8 Ma due to the eastern graben-boundary fault resulting in the appearance of a paleolake.Following by a geologically quiet period about 8-2.5 Ma,the paleolake expanded from east to west at around 8-6 Ma reaching its maximum at ca.6 Ma.Then,the graben was broken at about 2.5 Ma.At last,the development of the glacier separated the graben into two parts that were Pagri and Duoqing Co since the later stages of the Middle Pleistocene.The evolution process suggested that the former three stages were related to the tectonic movement,which determined the basement of the graben,while the last stage may have been influenced by glacial activity caused by climate change.展开更多
The marginal areas of the Tibetan Plateau have great vertical altitude gradient and abundant vegetation, they are therefore the ideal places for investigating the relationships among carbon isotope composition(δ^(13)...The marginal areas of the Tibetan Plateau have great vertical altitude gradient and abundant vegetation, they are therefore the ideal places for investigating the relationships among carbon isotope composition(δ^(13)C) of modern soils, vegetation and environmental factors, which would be very useful for the reconstructions of both paleovegetation and paleoclimate. In this paper, modern soil samples collected in different vegetation vertical zones along 4km elevation gradient in the eastern margin of the Tibetan Plateau were analyzed for their carbon isotope composition. The results show that the modern soils in different vegetation vertical zones show apparent difference of δ^(13)C values, which get heavier in the sequence of mixed evergreen and deciduous broad-leaved forest(-27.28‰ on average), evergreen broad-leaved forest(-27.25‰), subalpine shrub-meadow(-25.81‰), subalpine coniferous forest(-25.81‰), alpine bush-meadow(-25.16‰), and drought-enduring shrub(-24.07‰). 1800 m and 3500 m are two critical points for the δ^(13)C values with respect to altitude. Specifically, the δ^(13)C values decrease with increasing altitude below both points while increasing with increasing altitude above both points. Further analyses indicate that the declining δ^(13)C values are mainly controlled by the decreasing proportion of C4 plants with elevation and the increasing δ^(13)C values are attributed to the plant physic-morphological adaptation to the alpine environment. In the absence of drought stress, temperature is the main controlling factor for the carbon isotopic variations with altitude gradient.展开更多
Objective The nearly parallel N-S-trending rifts in southern Tibet represent the E-W extension of the Tibet Plateau. Most data which constrained the age of the extensional deformation come from isotopic dating of the...Objective The nearly parallel N-S-trending rifts in southern Tibet represent the E-W extension of the Tibet Plateau. Most data which constrained the age of the extensional deformation come from isotopic dating of the dikes probably related to the activity of the nearly N-S faulting and micas from hydrothermal activity and the low- temperature thermochronology of plateau uplift. Previous research shows that there are at least three different ideas about the age of the rifts： （1） older than 16-12 Ma, （2） 14- 10 Ma, and （3） 8-4 Ma （Fig. la）. For the old sedimentary strata represented the beginning of the rifting, the dating of the sediments helps to better define the initial rifting age.展开更多
The hazard assessment of potential earthquake-induced landslides is an important aspect of the study of earthquake-induced landslides. In this study, we assessed the hazard of potential earthquake-induced landslides i...The hazard assessment of potential earthquake-induced landslides is an important aspect of the study of earthquake-induced landslides. In this study, we assessed the hazard of potential earthquake-induced landslides in Huaxian County with a new hazard assessment method. This method is based on probabilistic seismic hazard analysis and the Newmark cumulative displacement assessment model. The model considers a comprehensive suite of information, including the seismic activities and engineering geological conditions in the study area, and simulates the uncertainty of the intensity parameters of the engineering geological rock groups using the Monte Carlo method. Unlike previous assessment studies on ground motions with a given exceedance probability level, the hazard of earthquake-induced landslides obtained by the method presented in this study allows for the possibility of earthquake-induced landslides in different parts of the study area in the future. The assessment of the hazard of earthquake-induced landslides in this study showed good agreement with the historical distribution of earthquake-induced landslides. This indicates that the assessment properly reflects the macroscopic rules for the development of earthquake-induced landslides in the study area, and can provide a reference framework for the management of the risk of earthquakeinduced landslides and land planning.展开更多
The Yangtze River Economic Belt(YREB)spans three terrain steps in China and features diverse topography that is characterized by significant differences in geological structure and presentday crustal deformation.Activ...The Yangtze River Economic Belt(YREB)spans three terrain steps in China and features diverse topography that is characterized by significant differences in geological structure and presentday crustal deformation.Active faults and seismic activity are important geological factors for the planning and development of the YREB.In this paper,the spatial distribution and activity of 165 active faults that exist along the YREB have been compiled from previous findings,using both remote-sensing data and geological survey results.The crustal stability of seven particularly noteworthy typical active fault zones and their potential effects on the crustal stability of the urban agglomerations are analyzed.The main active fault zones in the western YREB,together with the neighboring regional active faults,make up an arc fault block region comprising primarily of Sichuan-Yunnan and a“Sichuan-Yunnan arc rotational-shear active tectonic system”strong deformation region that features rotation,shear and extensional deformation.The active faults in the central-eastern YREB,with seven NE-NNE and seven NW-NWW active faults(the“7-longitudinal,7-horizontal”pattern),macroscopically make up a“chessboard tectonic system”medium-weak deformation region in the geomechanical tectonic system.They are also the main geological constraints for the crustal stability of the YREB.展开更多
基金supported by National Natural Science foundation of China(grants No.41571013)China Geology Survey project(grants No.DD20160268)Institute of Geomechanics,Chinese academy of geological sciences basal research fund(grants No.DZLXJK201702)
文摘The 1515 M7/4 Yongsheng earthquake is the strongest earthquake historically in northwest Yunnan.However,its time,magnitude and the seismogenic fault have long been a topic of dispute.In order to accurately define those problems,a 1:50000 active tectonic mapping was carried out along the northern segment of the Chenghai-Binchuan fault zone.The result shows that there is an at least 25 km-long surface rupture and a series of seismic landslides distributed along the Jinguan fault and the Chenghai fault.Radiocarbon dating of the 14C samples indicates that the surface rupture should be a part of the deformation zone caused by the Yongsheng earthquake in the year 1515.The distribution characteristics of this surface rupture indicate that the macroscopic epicenter of the 1515 Yongsheng earthquake may be located near Hongshiya,and the seismogenic fault of this earthquake is the Jinguan-Chenghai fault,the northern part of the Chenghai-Binchuan fault zone.Striations on the surface rupture show that the latest motion of the fault is normal faulting.The maximum co-seismic vertical displacement can be 3.8 m,according to the empirical formula for the fault displacement and moment magnitude relationship,the moment magnitude of the Yongsheng earthquake was Mw 7.3-7.4.Furthermore,combining published age data with the 14C data in this paper reveals that at least four large earthquakes of similar size to the 1515 Yongsheng earthquake,have taken place across the northern segment of the Chenghai-Binchuan fault zone since 17190~50 yr.BP.The in-situ recurrence interval of Mw 7.3-7.4 characteristic earthquakes in Yongsheng along this fault zone is possibly on the order of 6 ka.
基金supported by National Natural foundation of China(grants No.41571013)China Geology Survey project(grants No.DD20160268)
文摘The north trending rifts in southern Xizang represent the E-W extension of the plateau and confirming the initial rifting age is key to the study of mechanics of these rifts.Pagri-Duoqing Co graben is located at southern end of Yadong-Gulu rift,where the late Cenozoic sediments is predominately composed of fluvio-lacustrine and moraine.Based on the sedimentary composition and structures,the fluviolacustrine could be divided into three facies,namely,lacustrine,lacustrine fan delta and alluvial fan.The presence of paleo-currents and conglomerate components and the provenance of the strata around the graben indicate that it was Tethys Himalaya and High Himalaya.Electron spin resonance(ESR)dating and paleo-magnetic dating suggest that the age of the strata ranges from ca.1.2 Ma to ca.8 Ma.Optically stimulated luminescence(OSL)dating showed that moraine in the graben mainly developed from around181-109 ka(late Middle Pleistocene).Combining previous data about the Late Cenozoic strata in other basins,it is suggested that 8-15 Ma may be the initial rifting time.Together with sediment distribution and drainage system,the sedimentary evolution of Pagri could be divided into four stages.The graben rifted at around 15-8 Ma due to the eastern graben-boundary fault resulting in the appearance of a paleolake.Following by a geologically quiet period about 8-2.5 Ma,the paleolake expanded from east to west at around 8-6 Ma reaching its maximum at ca.6 Ma.Then,the graben was broken at about 2.5 Ma.At last,the development of the glacier separated the graben into two parts that were Pagri and Duoqing Co since the later stages of the Middle Pleistocene.The evolution process suggested that the former three stages were related to the tectonic movement,which determined the basement of the graben,while the last stage may have been influenced by glacial activity caused by climate change.
基金supported by the National Natural Science Foundation of China (grant nos. 41888101, 41907377 and 41772383)the Special Fund for Basic Scientific Research of China University of Geosciences (grant no. 53200859557)。
文摘The marginal areas of the Tibetan Plateau have great vertical altitude gradient and abundant vegetation, they are therefore the ideal places for investigating the relationships among carbon isotope composition(δ^(13)C) of modern soils, vegetation and environmental factors, which would be very useful for the reconstructions of both paleovegetation and paleoclimate. In this paper, modern soil samples collected in different vegetation vertical zones along 4km elevation gradient in the eastern margin of the Tibetan Plateau were analyzed for their carbon isotope composition. The results show that the modern soils in different vegetation vertical zones show apparent difference of δ^(13)C values, which get heavier in the sequence of mixed evergreen and deciduous broad-leaved forest(-27.28‰ on average), evergreen broad-leaved forest(-27.25‰), subalpine shrub-meadow(-25.81‰), subalpine coniferous forest(-25.81‰), alpine bush-meadow(-25.16‰), and drought-enduring shrub(-24.07‰). 1800 m and 3500 m are two critical points for the δ^(13)C values with respect to altitude. Specifically, the δ^(13)C values decrease with increasing altitude below both points while increasing with increasing altitude above both points. Further analyses indicate that the declining δ^(13)C values are mainly controlled by the decreasing proportion of C4 plants with elevation and the increasing δ^(13)C values are attributed to the plant physic-morphological adaptation to the alpine environment. In the absence of drought stress, temperature is the main controlling factor for the carbon isotopic variations with altitude gradient.
基金supported by the National Natural Science Foundation of China(grant No.41571013)Project of China Geological Survey(grant No.12120114002101)
文摘Objective The nearly parallel N-S-trending rifts in southern Tibet represent the E-W extension of the Tibet Plateau. Most data which constrained the age of the extensional deformation come from isotopic dating of the dikes probably related to the activity of the nearly N-S faulting and micas from hydrothermal activity and the low- temperature thermochronology of plateau uplift. Previous research shows that there are at least three different ideas about the age of the rifts： （1） older than 16-12 Ma, （2） 14- 10 Ma, and （3） 8-4 Ma （Fig. la）. For the old sedimentary strata represented the beginning of the rifting, the dating of the sediments helps to better define the initial rifting age.
基金funded by the National Natural Science Foundation of China(41572313)Geological Survey Project(12120114035501)the China National Special Fund for Earthquake Scientific Research(201408014)
文摘The hazard assessment of potential earthquake-induced landslides is an important aspect of the study of earthquake-induced landslides. In this study, we assessed the hazard of potential earthquake-induced landslides in Huaxian County with a new hazard assessment method. This method is based on probabilistic seismic hazard analysis and the Newmark cumulative displacement assessment model. The model considers a comprehensive suite of information, including the seismic activities and engineering geological conditions in the study area, and simulates the uncertainty of the intensity parameters of the engineering geological rock groups using the Monte Carlo method. Unlike previous assessment studies on ground motions with a given exceedance probability level, the hazard of earthquake-induced landslides obtained by the method presented in this study allows for the possibility of earthquake-induced landslides in different parts of the study area in the future. The assessment of the hazard of earthquake-induced landslides in this study showed good agreement with the historical distribution of earthquake-induced landslides. This indicates that the assessment properly reflects the macroscopic rules for the development of earthquake-induced landslides in the study area, and can provide a reference framework for the management of the risk of earthquakeinduced landslides and land planning.
基金This research is funded by the China Geological Survey project(DD20160268).
文摘The Yangtze River Economic Belt(YREB)spans three terrain steps in China and features diverse topography that is characterized by significant differences in geological structure and presentday crustal deformation.Active faults and seismic activity are important geological factors for the planning and development of the YREB.In this paper,the spatial distribution and activity of 165 active faults that exist along the YREB have been compiled from previous findings,using both remote-sensing data and geological survey results.The crustal stability of seven particularly noteworthy typical active fault zones and their potential effects on the crustal stability of the urban agglomerations are analyzed.The main active fault zones in the western YREB,together with the neighboring regional active faults,make up an arc fault block region comprising primarily of Sichuan-Yunnan and a“Sichuan-Yunnan arc rotational-shear active tectonic system”strong deformation region that features rotation,shear and extensional deformation.The active faults in the central-eastern YREB,with seven NE-NNE and seven NW-NWW active faults(the“7-longitudinal,7-horizontal”pattern),macroscopically make up a“chessboard tectonic system”medium-weak deformation region in the geomechanical tectonic system.They are also the main geological constraints for the crustal stability of the YREB.
