Based on the physical model of Brownian passage time,the probabilities of recurrence of strong earthquakes on the major active faults in China are calculated in different predictive time spans,based mainly on the anal...Based on the physical model of Brownian passage time,the probabilities of recurrence of strong earthquakes on the major active faults in China are calculated in different predictive time spans,based mainly on the analysis of the earthquake preparation process before a strong earthquake occurs. Furthermore,the seismic risks on active faults are studied. The results show that the earthquake probabilities on the Xianshuihe fault,the Altyn Tagh fault,the east Kunlun fault and Xiaojiang fault are significantly greater than other faults in the Chinese mainland,which indicates that the level of stress accumulation on these faults are higher than on other faults. Therefore,these faults may have a seismic risk for strong earthquake in future.展开更多
The regional tectonic background and characteristics of active faults of the Yutian MS7.3earthquake on February 12,2014 are discussed in this paper.After the analysis of the epicenter area of the MS7.3 earthquake in 2...The regional tectonic background and characteristics of active faults of the Yutian MS7.3earthquake on February 12,2014 are discussed in this paper.After the analysis of the epicenter area of the MS7.3 earthquake in 2014 and the focal mechanisms of the former strong earthquakes around it,the authors deduced that the seismogenic fault of the MS7.3earthquake is the east branch of the Ashikule fault.The MS7.3 earthquake in 2014 and the MS7.3 earthquake in 2008 are two strong earthquake events on the different sections of the Altun Tagh fault,where the fault behavior changes from sinistral slip to normal faulting because of the extensional tail effects in the southern end of the Altun Tagh fault.It is concluded that the two MS7.3 earthquakes have the same dynamic source,and the MS7.3earthquake in 2008 promoted the occurrence of the MS7.3 earthquake in 2014.Finally,we calculate the Coulomb stress change to the seismogenic fault of the MS7.3 earthquake in2014 from the MS7.3 earthquake in 2008 using the layered crust model.The result also shows that the MS7.3 earthquake in 2008 accelerated the occurrence of the MS7.3earthquake in 2014.展开更多
On April 20, 2013, the Lushan M^7.0 earthquake struck at the southern part of the Longmenshan fault in the eastern Tibetan Plateau, China. The shear-wave splitting in the crust indicates a connection between the direc...On April 20, 2013, the Lushan M^7.0 earthquake struck at the southern part of the Longmenshan fault in the eastern Tibetan Plateau, China. The shear-wave splitting in the crust indicates a connection between the direction of the principal crustal com- pressive stress and the fault orientation in the Longmenshan fault zone. Our relocation analysis of the aftershocks of the Lushan earthquake shows a gap between the location of the rupture zone of the Lushan Ms7.0 earthquake and that of the rup- ture zone of the Wenchuan MsS.0 earthquake. We believe that stress levels in the crust at the rupture gap and its vicinity should be monitored in the immediate future. We suggest using controlled source borehole measurements for this purpose.展开更多
Although there are many earthquake relics preserved in the southeast segment of the Ganzi-Yushu Fault in the central Tibetan Plateau,the recurrence regularity of paleoearthquakes is not yet clear.This work studies pal...Although there are many earthquake relics preserved in the southeast segment of the Ganzi-Yushu Fault in the central Tibetan Plateau,the recurrence regularity of paleoearthquakes is not yet clear.This work studies paleoearthquakes on this fault segment since the Holocene through geomorphic investigation and trench excavation.The results show that sinistral dislocation of the T3/T2 terrace boundary is up to 80 m at the Cuoa Township.A 1.5 m-high fault scarp extends 3 km near the Renguo Township.A number of paleoearthquakes are exposed in trenches at two places,respectively.In combination with historical records,our work has identified 5 or 6 paleoearthquakes on this fault segment since last 5600 years.The occurrence times and recurrence intervals of these paleoearthquakes are estimated by 14C dating on strata in the trenches.Our analysis shows that these paleoearthquakes do not exhibit evident periodicity,but instead show a clustering characteristic.From 5600 a to present,seismicity of the southeastern segment of the Ganzi-Yushu Fault has two active periods and one quiet period,and the present-day time is just in the second active epoch.The recurrence intervals of each active epoch are different:1000-1300 a in the first one,534 a in the second one.展开更多
Composite borehole profiling combined with trenching is an effective way to acquire evidence of past ruptures of buffed active faults. In this study, three composite borehole profiles and a large-scale trench excavati...Composite borehole profiling combined with trenching is an effective way to acquire evidence of past ruptures of buffed active faults. In this study, three composite borehole profiles and a large-scale trench excavation were carded out across the surface rupture zone of the 1976 Ms7.8 Tangshan earthquake. The following three major conclusions have been reached. （1） The surface rupture zone of the 1976 earthquake extends more than 47 km long to the south of Tangshan city, passing to the west of Sunjialou, to Daodi town in Fengnan County, to Xihe in Fengnan County. （2） The surface rupture zone is divided into south and north branches. The north branch has mainly fight-lateral strike-slip motion, and the vertical displacement of the surface is up on the west and down on the east. On the other hand, the vertical displacement of the south branch is up on the east and down on the west, accompanied by some right-lateral slip. Such a faulting style cannot be explained by the movement of a single normal or reverse fault, but is consistent with the vertical displacement field induced by the fight-lateral strike-slip of the fault belt. The drilling and trenching data from this study verify that such activity continued through the Late Quaternary on the Tangshan Fault. （3） The fault planes exhumed by trenching and the dislocations of strata revealed by the boreholes indicate that multiple faulting events occurred on the Tangshan Fault in the Late Quaternary. The timing of three ruptures prior to the 1976 earthquake was 7.61-8.13, 〉14.57, and 24.21-26.57 ka BP. Counting the earthquake of 1976, the recurrence interval of the four strong events is about 6.7 to 10.8 ka. On one of the three borehole profiles, the Niumaku profile, nine faulting events were detected since 75.18 ka BP with an average interval of 8.4 ka. In addition, this paper also discusses the difference between the Late Quaternary sedimentary environments to the north and south of Tangshan city based on stratum dating.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.41104036)
文摘Based on the physical model of Brownian passage time,the probabilities of recurrence of strong earthquakes on the major active faults in China are calculated in different predictive time spans,based mainly on the analysis of the earthquake preparation process before a strong earthquake occurs. Furthermore,the seismic risks on active faults are studied. The results show that the earthquake probabilities on the Xianshuihe fault,the Altyn Tagh fault,the east Kunlun fault and Xiaojiang fault are significantly greater than other faults in the Chinese mainland,which indicates that the level of stress accumulation on these faults are higher than on other faults. Therefore,these faults may have a seismic risk for strong earthquake in future.
基金funded by the Spark Program of Earthquake Science of China(XH15047Y)the National Science Foundation of China(41404043)
文摘The regional tectonic background and characteristics of active faults of the Yutian MS7.3earthquake on February 12,2014 are discussed in this paper.After the analysis of the epicenter area of the MS7.3 earthquake in 2014 and the focal mechanisms of the former strong earthquakes around it,the authors deduced that the seismogenic fault of the MS7.3earthquake is the east branch of the Ashikule fault.The MS7.3 earthquake in 2014 and the MS7.3 earthquake in 2008 are two strong earthquake events on the different sections of the Altun Tagh fault,where the fault behavior changes from sinistral slip to normal faulting because of the extensional tail effects in the southern end of the Altun Tagh fault.It is concluded that the two MS7.3 earthquakes have the same dynamic source,and the MS7.3earthquake in 2008 promoted the occurrence of the MS7.3 earthquake in 2014.Finally,we calculate the Coulomb stress change to the seismogenic fault of the MS7.3 earthquake in2014 from the MS7.3 earthquake in 2008 using the layered crust model.The result also shows that the MS7.3 earthquake in 2008 accelerated the occurrence of the MS7.3earthquake in 2014.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41174042, 41040034)the China National Special Fund for Earthquake Scientific Research in Public Interest (Grant No. 201008001)
文摘On April 20, 2013, the Lushan M^7.0 earthquake struck at the southern part of the Longmenshan fault in the eastern Tibetan Plateau, China. The shear-wave splitting in the crust indicates a connection between the direction of the principal crustal com- pressive stress and the fault orientation in the Longmenshan fault zone. Our relocation analysis of the aftershocks of the Lushan earthquake shows a gap between the location of the rupture zone of the Lushan Ms7.0 earthquake and that of the rup- ture zone of the Wenchuan MsS.0 earthquake. We believe that stress levels in the crust at the rupture gap and its vicinity should be monitored in the immediate future. We suggest using controlled source borehole measurements for this purpose.
基金supported by the Yushu Earthquake Science Investigation of China Earthquake Administration
文摘Although there are many earthquake relics preserved in the southeast segment of the Ganzi-Yushu Fault in the central Tibetan Plateau,the recurrence regularity of paleoearthquakes is not yet clear.This work studies paleoearthquakes on this fault segment since the Holocene through geomorphic investigation and trench excavation.The results show that sinistral dislocation of the T3/T2 terrace boundary is up to 80 m at the Cuoa Township.A 1.5 m-high fault scarp extends 3 km near the Renguo Township.A number of paleoearthquakes are exposed in trenches at two places,respectively.In combination with historical records,our work has identified 5 or 6 paleoearthquakes on this fault segment since last 5600 years.The occurrence times and recurrence intervals of these paleoearthquakes are estimated by 14C dating on strata in the trenches.Our analysis shows that these paleoearthquakes do not exhibit evident periodicity,but instead show a clustering characteristic.From 5600 a to present,seismicity of the southeastern segment of the Ganzi-Yushu Fault has two active periods and one quiet period,and the present-day time is just in the second active epoch.The recurrence intervals of each active epoch are different:1000-1300 a in the first one,534 a in the second one.
基金supported by the Fundamental Research Funds of Institute of Crustal Dynamics,China Earthquake Adminishtration (Grant No. ZDJ2007-1)
文摘Composite borehole profiling combined with trenching is an effective way to acquire evidence of past ruptures of buffed active faults. In this study, three composite borehole profiles and a large-scale trench excavation were carded out across the surface rupture zone of the 1976 Ms7.8 Tangshan earthquake. The following three major conclusions have been reached. （1） The surface rupture zone of the 1976 earthquake extends more than 47 km long to the south of Tangshan city, passing to the west of Sunjialou, to Daodi town in Fengnan County, to Xihe in Fengnan County. （2） The surface rupture zone is divided into south and north branches. The north branch has mainly fight-lateral strike-slip motion, and the vertical displacement of the surface is up on the west and down on the east. On the other hand, the vertical displacement of the south branch is up on the east and down on the west, accompanied by some right-lateral slip. Such a faulting style cannot be explained by the movement of a single normal or reverse fault, but is consistent with the vertical displacement field induced by the fight-lateral strike-slip of the fault belt. The drilling and trenching data from this study verify that such activity continued through the Late Quaternary on the Tangshan Fault. （3） The fault planes exhumed by trenching and the dislocations of strata revealed by the boreholes indicate that multiple faulting events occurred on the Tangshan Fault in the Late Quaternary. The timing of three ruptures prior to the 1976 earthquake was 7.61-8.13, 〉14.57, and 24.21-26.57 ka BP. Counting the earthquake of 1976, the recurrence interval of the four strong events is about 6.7 to 10.8 ka. On one of the three borehole profiles, the Niumaku profile, nine faulting events were detected since 75.18 ka BP with an average interval of 8.4 ka. In addition, this paper also discusses the difference between the Late Quaternary sedimentary environments to the north and south of Tangshan city based on stratum dating.
