Mechanism of Landslides Triggered by the 1990 Iran Earthquake

Abstract

The June 1990 Manjil earthquake that shocked Gilan and Zanjan provinces of Iran (in north and northwestern Iran) provoked several landslides in the region over the south part of Alborz mountains. Two of these landslides (the Galdian and the Fatalak landslides) were selected to be discussed in this paper. Samples were collected from these landslides. Shear tests were carried our using the newly-developed cyclic loading ring shear apparatus. The stress condition in slopes during earthquake was approximately reproduced. The results of the tests were used for interpreting the mechanism of high velocity motion in the Fatalak landslide and in the upper part of Galdian landslide during the main shock, and the intermittent low velocity motion in the lower part of the Galdian landslide during the following two weeks after the main shock.