FORMATION MECHANISM OF GROUND FISSURES UNDER VOLCANIC ACTIVITY IN EAST AFRICAN RIFT

In Kenyan part of the East African Rift,the magmatism related to asthenosphere intrusion and lithospheric thinning leads to frequent volcanic activities. The ground fissures caused by volcanic activity directly threaten the engineering facilities in the study area. The purposes of this paper are (a) to determine the distribution characteristics of the ground fissures,(b) to analyze the correlation between ground fissures and volcanic activities,and (c) to explore the formation mechanism of the ground fissures. Through field investigation and geophysical exploration,this paper summarizes the plane distribution characteristics and failure characteristics of the ground fissures,analyzes the relationship between the bedrock fissures and the ground fissures. The results show that the ground fissures are mainly distributed at the bottom of the rift,accompanied by volcanoes. The strikes of ground fissures are mainly NE-NNE and NW,extending linearly on the ground surface. The characteristics of surface failure are mainly horizontal tension. The ground fissures in sediments are connected with the bedrock fissures. The bedrock fissures determine the development location and scale of the ground fissures. The relationship between volcanic activity and the ground fissures is examined by crustal deformation data and the Mogi point source model. The formation mechanism of the ground fissures under volcanic activity is summarized. The widespread discontinuous deformation is caused by volcanic eruption resulted in bedrock rupture. The formation mechanism of the ground fissures in Kenya Rift Valley can be summarized as volcanic eruption-bedrock rupture-sediment destruction.