The Luhuatai fault is one of the important buried tectonics in the Yinchuan basin. Based on the results of shallow seismic exploration, we conducted composite drilling section exploration and dating of the samples fro...The Luhuatai fault is one of the important buried tectonics in the Yinchuan basin. Based on the results of shallow seismic exploration, we conducted composite drilling section exploration and dating of the samples from boreholes. Some useful data was obtained, such as the depth of the upper breaking point, the latest activity age, displacement in the late Quaternary, and slip rates, etc. This study shows that the activity is different between the north and south segment along the Luhuatai fault. The north segment is a Holocene fault, while the south segment is a late mid-Pleistocene fault. From north to south along the north segment of Luhuatai fault, the activity has been enhanced, and the faulting is stronger in late Pleistocene than Holocene.展开更多
The paper introduces the steps and methods of multi-approach, multi-level exploration of buried faults in thick Quaternary sediment regions by taking the test exploration of the Yinchuan active fault as example. Based...The paper introduces the steps and methods of multi-approach, multi-level exploration of buried faults in thick Quaternary sediment regions by taking the test exploration of the Yinchuan active fault as example. Based on the comprehensive analyses of previous data, we choose the Xinqushao Village of Xingqing District of Yinchuan City as the test site for the comprehensive exploration. Firstly, we adopted shallow seismic investigation with group intervals of 10m, 5m and lm to gradually trace layer by layer the master fault of the Yinchuan buried fault from a deep depth to a shallow depth where drilling could be used. Then, with composite geological profile drilling, we determined the precise location and dip angle of the fault. The drilling show the buried depth of the upper offset point is 8.3m. Finally, large-scale trenching revealed that the actual buried depth of the upper offset point of the fault is 1.5m from the ground surface and there are paleoearthquake events of 5 stages. Combined with the preliminary result of corresponding sample age, we conclude the Yinchuan buried fault is a mid to late Holocene active fault.展开更多
The kinematic characteristics of the Sanguankou-Niushoushan fault（SGK-NSSF） are of great significance to the understanding of the extension of the arc tectonic belt in the northeastern margin of the Tibet Plateau. U...The kinematic characteristics of the Sanguankou-Niushoushan fault（SGK-NSSF） are of great significance to the understanding of the extension of the arc tectonic belt in the northeastern margin of the Tibet Plateau. Using field surveys and various data collection methods, including large-scale geological mapping, measurement of typical topographies, and dating of sedimentary strata, it was determined that the SGK-NSSF exhibits obvious dextral strike-slip characteristics and thus is not a sinistral strike-slip fault, as believed by previous researchers. The results of this study show that the geological boundaries for the Paleozoic, Mesozoic, and Cenozoic eras were all dextrally dislocated by the fault, with the faulted displacements being similar. The maximum strike-slip displacement of the fault, after elimination of topographic effects, was found to be 961±6 m. The Sanguankou fault at the northern section exhibits obvious characteristics of more recent activities, with a series of small gullies having undergone synchronized dextral writhing after traversing the fault. The average horizontal slip rate of the fault since the late Quaternary was determined to be approximately 0.35 mm/a. The pre-existing fold structures formed during the late Pliocene were dislocated by the fault and became ex situ, indicating that dextral strike-slip of the fault could not have occurred prior to the late Pliocene. The maximum displacements and average slip rates were used to estimate the onset time of the dextral strike-slip activities of the fault as being after 2.7 Ma. In this study, the understanding of previous researchers concerning the extension in the northeastern margin of the Tibet Plateau was combined with analyses of the successive relationships between fold deformations and fault activities. This led to the finding that the extension in the northeastern margin of the Tibet Plateau reached the vicinity of the SGK-NSSF during the late Pliocene（~2.7 Ma）, causing regional uplift and fold deformations of the strata there. During the early Quaternary, the northeastern compression of the Tibet Plateau and the counterclockwise rotation of the Ordos block collectively resulted in the dextral strike-slip activities of the SGK-NSSF. This then formed the foremost margin of the arc tectonic belt extension in the northeastern margin of the Tibet Plateau.展开更多
基金funded by the Special R&D Fund for Earthquake Study,China (201008003)
文摘The Luhuatai fault is one of the important buried tectonics in the Yinchuan basin. Based on the results of shallow seismic exploration, we conducted composite drilling section exploration and dating of the samples from boreholes. Some useful data was obtained, such as the depth of the upper breaking point, the latest activity age, displacement in the late Quaternary, and slip rates, etc. This study shows that the activity is different between the north and south segment along the Luhuatai fault. The north segment is a Holocene fault, while the south segment is a late mid-Pleistocene fault. From north to south along the north segment of Luhuatai fault, the activity has been enhanced, and the faulting is stronger in late Pleistocene than Holocene.
基金The research was jointly sponsored by the National Development and Reform Commission of China under the project of"Experimental Exploration of Active Fault in Urban Area"(20041138)by National Natural Science Foundation of China (40234040)
文摘The paper introduces the steps and methods of multi-approach, multi-level exploration of buried faults in thick Quaternary sediment regions by taking the test exploration of the Yinchuan active fault as example. Based on the comprehensive analyses of previous data, we choose the Xinqushao Village of Xingqing District of Yinchuan City as the test site for the comprehensive exploration. Firstly, we adopted shallow seismic investigation with group intervals of 10m, 5m and lm to gradually trace layer by layer the master fault of the Yinchuan buried fault from a deep depth to a shallow depth where drilling could be used. Then, with composite geological profile drilling, we determined the precise location and dip angle of the fault. The drilling show the buried depth of the upper offset point is 8.3m. Finally, large-scale trenching revealed that the actual buried depth of the upper offset point of the fault is 1.5m from the ground surface and there are paleoearthquake events of 5 stages. Combined with the preliminary result of corresponding sample age, we conclude the Yinchuan buried fault is a mid to late Holocene active fault.
基金supported by the Fundamental Research Funds in Institute of Geology, China Earthquake Administration (Grant No. IGCEA1220)Special Project on Earthquake Research (Grant No. 201308012)+1 种基金National Natural Science Foundation of China (Grant Nos. 41202158, 41372220 & 41590861)Science for Earthquake Resilience (Grant No. XH14052)
文摘The kinematic characteristics of the Sanguankou-Niushoushan fault（SGK-NSSF） are of great significance to the understanding of the extension of the arc tectonic belt in the northeastern margin of the Tibet Plateau. Using field surveys and various data collection methods, including large-scale geological mapping, measurement of typical topographies, and dating of sedimentary strata, it was determined that the SGK-NSSF exhibits obvious dextral strike-slip characteristics and thus is not a sinistral strike-slip fault, as believed by previous researchers. The results of this study show that the geological boundaries for the Paleozoic, Mesozoic, and Cenozoic eras were all dextrally dislocated by the fault, with the faulted displacements being similar. The maximum strike-slip displacement of the fault, after elimination of topographic effects, was found to be 961±6 m. The Sanguankou fault at the northern section exhibits obvious characteristics of more recent activities, with a series of small gullies having undergone synchronized dextral writhing after traversing the fault. The average horizontal slip rate of the fault since the late Quaternary was determined to be approximately 0.35 mm/a. The pre-existing fold structures formed during the late Pliocene were dislocated by the fault and became ex situ, indicating that dextral strike-slip of the fault could not have occurred prior to the late Pliocene. The maximum displacements and average slip rates were used to estimate the onset time of the dextral strike-slip activities of the fault as being after 2.7 Ma. In this study, the understanding of previous researchers concerning the extension in the northeastern margin of the Tibet Plateau was combined with analyses of the successive relationships between fold deformations and fault activities. This led to the finding that the extension in the northeastern margin of the Tibet Plateau reached the vicinity of the SGK-NSSF during the late Pliocene（~2.7 Ma）, causing regional uplift and fold deformations of the strata there. During the early Quaternary, the northeastern compression of the Tibet Plateau and the counterclockwise rotation of the Ordos block collectively resulted in the dextral strike-slip activities of the SGK-NSSF. This then formed the foremost margin of the arc tectonic belt extension in the northeastern margin of the Tibet Plateau.
