The Development Regularity And Seismic Geological Significance Of The Seismic Rockfall In Chenghai Fault Zone In Yunnan Province

The Chenghai fault zone is an important fault of northwest Yunnan during Quaternary.In bedrock mountains where the seismicity is active,collapse rockfalls is a common secondary mountain disaster of earthquake,the collapse rockfalls and other secondary mountain after the earthquake disaster can reflect the characteristics and laws of the earthquake from different angles and levels.Therefore,the corresponding relationship of seismic rockfalls' space-time distribution and ancient seismic events is very close.In this paper,it researched the development characteristics of falling rocks in the studied area and their relationship with Chenghai fault on the field geological investigation,used the U-series disequilibrium dating method to measure the secondary calcium thin films on the surface of rock falls and compared with other palaeoseismic traces' age in the region and previous research results.Then it discussed the relationship between the seismic rock fall and the ancient seismic events of Chenghai fault,and analyzed the earthquake seismic geological significance of rockfall.Gain the following understanding and achievement:(1)It investigated paleoseismic rockfalls' characteristics and distribution of Chenghai fault,and discussed the relationship between the distribution of the and the ancient seismic activity controlled by the Chenghai fault.The seismic rockfalls along the Chenghai fault has gregariousness and periods in the space-time distribution,which are associated with ancient landslides,and provides new materials and methods for the study of ancient earthquakes in Chenghai fault.(2)For the target location s typical seismic rockfall distribution area,we did Useries dating for the sample of rockfalls' Calcium film and ancient landslide fissure calcium film.The U-series age of the calcium film is approximately distributed at range of around 5 time periods,which are 338.53ka?348.02 ka BP?152.47ka?154.70 ka BP?91.56ka?97.70 ka BP ? 25.36ka?29.16 ka BP and 8.31ka?9.24 ka BP,showing that rockfalls mainly formed in the early Pleistocene to Holocene,and reflecting multiplestaged characteristics of the rockfalls' development.(3)Comparing the results of U-series dating with the ages of regional earthquake faults?earthquake fissure?ancient seismic sliding surface and so on,it can be obviously concluded that seismic rockfalls and ancient seismic events are closely associated.According to the comparative results of the ancient earthquake relics in the region and the previous studies,the eight ancient seismic events in the middle Pleistocene period were divided.(4)It discussed the seismic and geological significance of rockfalls in Chenghai fault.The distribution and development of different periods seismic rockfalls can indicate the geological disasters of different times such as the ancient earthquake events and the ancient landslides and rock slide.The time interval of the formation times of multi-period seismic rockfalls can reflect the tectonic activity of Chenghai fault to some extent.In this paper,it researched the causes and periods of rockfalls by using the U-series disequilibrium dating method to measure the secondary calcium thin films on the surface of rockfalls,and established the relationship between the ancient earthquake events and the rockfalls.Further on,it provided a new way of understanding the relationship between temporal and spatial relations of the ancient earthquake events and identifying ancient earthquake events.