DEFORMATION CHARACTERISTICS AND MECHANISM OF EARTH FISSURES IN KENYA RIFA VALLEY, EAST AFRICA

During the 2018 rainy season,a huge 7~8 km long earth fissure suddenly appeared on the surface of the Kenya Rift Valley,east African. The fissure directly caused the destruction of the B3 highway(this is called B3 earth fissure),the main road connecting the east and west regions of Kenya. However,the "Nairobi-Malaba Standard Gauge Railway",a key project of China's "One Belt One Road" initiative,is only a few kilometers away from this earth fissure. Scientific explanation of the mechanism and dynamic process of earth fissures is an important guarantee for the safe operation of railways. This paper focuses on the study of the spatial distribution and formation mechanism of the B3 earth fissure. The spatial position of the earth fissures is obtained by using satellite image interpretation and field surveys. The high-resolution numerical value of the fissure zone is established using structure for motion technology. Detailed measurements are performed on this basis. Field investigations reveal that the B3 earth fissure is developed on the F₄ active fault at the eastern boundary of the Kenya rift,and its spatial position is controlled by the F₄ fault. The vertical profile of the earth fissure reveals that the Holocene sediments are obviously faulted and there are multiple fractured planes running through it. The pyroclastic rock layers under the earth fissures have obvious tensile cracks. The cracks become channels for surface water to seep downward during the rainy period,and cause the loose sediments on the shallow surface to migrate downwards. The north-south active faults system developed in the Kenya Rift Valley is the main channel for groundwater flow during the rainy period. These processes cause groundwater runoff to continuously erode the subsurface layer,surface materials to be transported downwards,which results in large-scale surface cracking and collapse. As a result,earth fissures in the Kenya Rift Valley are controlled by the spatial distribution of active faults in this area.