Effect Of Loess Seismic Landslides Controlled By Strike-slip Fault

The Loess Plateau is one of the regions most hit by strong earthquakes and severe geological disasters in China.Earthquake-induced loess landslides are the leading cause of casualties and economic losses in the region.This study conducted a field survey of the loess seismic landslides,specifically on their widespread coverage and disaster severity.The focus was placed on the magnitude-8.0 1654 Tianshuinan earthquake and the 1920 magnitude-8.5 Haiyuan earthquake,and interpretations were given based on Google Earth's satellite images.Statistical analyses were carried out on the distribution patterns and development characteristics of the loess landslides induced by both the above earthquakes,while the loess seismic landslide effect dictated by strike-slip faults was studied.The findings lay a foundation for further research on the disaster formation and risk assessment of loess seismic landslides,hence offering significant application value in engineering.The main content and research findings of this study are as follows:(1)Statistical analyses were conducted of the distribution pattern and development characteristics of the loess landslides induced by the 1654 Tianshuinan earthquake.Picking up from the concise description of the damage inflicted by the magnitude-8.0earthquake,the relationship of 745 loess seismic landslides with seismic intensity,epicentral distance,fault distance,geomorphology,and loess thickness was explored.Afterward,the landslides geometric,morphological,directional,and kinematic characteristics were examined using a pre-established database of the induced loess landslides.The results are laid out as follows.The resulting loess landslides are concentrated within the seismic intensity range of???.The epicentral distances of the vast majority of loess landslides are within the scope of 35?60 km,and the fault widths are no greater than 30 km.The dominant slope angles of slide development range from 10°to 20°and the development degrees are greatly affected by the loess ridge direction and the loess thickness.Landslides with volumes(V)over 1 million m~3exceed 70%,the equivalent friction coefficients(?)are concentrated with 0.20?0.35,and the remote sliding features are more obvious.The empirical relationship between the equivalent friction coefficients,the maximum horizontal distance of the landslide(L_max),the maximum vertical distance of the landslide(H_max)and the volume of the landslide are:?=0.6347V^-0.188(R~2=0.6045),L_max=102.3484 V ^0.3589(R~2=0.7858),H_max=57.0009 V ^0.2161(R~2=0.6013).(2)Statistical analyses of the distribution patterns and development characteristics of loess landslides induced by the 1920 magnitude-8.5 Haiyuan earthquake were also conducted.The relationship of 568 loess seismic landslides with seismic intensity,epicentral distance,fault distance,geomorphology and loess thickness was explored,and the geometric,morphological,directional,and kinematic characteristics of the landslides were explored based on a pre-established database of the induced loess landslides.The results are presented as follows.The loess landslides are concentrated in the?seismic intensity zone.Landslides with 75?110 km epicentral distances and45?65 km fault widths are the most developed,while the dominant slope angles of slide development range from 10°to 20°,and the development degree is closely related to the loess'topography and thickness.The most apparent main sliding directions of the landslides are along the slope angle,and the sliding directions are prominently dictated by the seismic wave propagation direction.The volumes(V)of the vast majority of landslides are greater than 1 million m~3,while the equivalent friction coefficients(?)of landslides range between 0.10 and 0.20,giving rise to the obvious remote sliding characteristic and mobility characteristic.The empirical relationship between the equivalent friction coefficients,the maximum horizontal distance of the landslide(L_max),the maximum vertical distance of the landslide(H_max)and the volume of the landslide are:?=0.2967V^-0.1378(R~2=0.5942),L_max=74.9897 V ^0.4169(R~2=0.6544),H_max=23.9852 V ^0.2675(R~2=0.5685).(3)The seismic landslide effect of loess controlled by strike-slip fault is studied,and the generating conditions of loess seismic landslide are summarized.Based on the distribution and development characteristics of loess landslide induced by the 1654Tianshuinan earthquake and the 1920 Haiyuan earthquake,the loess earthquake landslide effect under the nature of the strike-slip fault is investigated,and the formation conditions of loess earthquake landslide are summarized.The results suggest that the back slope effect,low position remote effect,and directional effect are the common characteristics of loess landslides induced by the Tianshuinan earthquake and Haiyuan earthquake,which can well reflect the control effect of slip fault on loess seismic landslides.The formation of loess seismic landslides can be treated as a comprehensive embodiment of seismic intensity,fault structure,geomorphology,and loess thickness.