Seismological, Soil and Valley Effects in Kirovakan, 1988 Armenia Earthquake

Abstract

There is substantial evidence that the city of Kirovakan, Armenia, despite its proximity (10 km) to the fault, experienced in general very small intensity of shaking during the 1988 earthquake. Moreover, the distribution of damage in the city was very nonuniform. In this paper, first, arguments are presented to show that seismological and geologic factors, relating to the generation and transmission of the seismic waves, could explain the unusually weak base excitation in Kirovakan. Then, the results of one‐dimensional (1D) wave‐propagation analysis, using soil profiles with field and laboratory measured parameters, are presented to explain the damage statistics in five zones into which the city was divided. 1D analyses of wave amplification in soil are found to provide adequate answers for zones where the underlying soils consist of less than 30 m dense gravelly sands and stiff clays. However, such analyses fail to explain the disproportionately large degree of damage observed only in one region, where soil profile constitutes a triangular sedimentary basin with maximum soil depth of about 150 m and width‐to‐depth ratio of about 5. A simplified three‐dimensional wave‐propagation analysis of the “valley” effects on ground‐surface motions, provides a better explanation of the observed damage.