SEISMOLOGICAL, SOIL AND VALLEY EFFECTS IN KIROVAKAN, 1988 ARMENIA EARTHQUAKE

There is substantial evidence that the city of Kirovakan, Armenia, des pite its proximity (10 km) to the fault, experienced in general very s mall intensity of shaking during the 1988 earthquake. Moreover, the di stribution of damage in the city was very nonuniform. In this paper, f irst, arguments are presented to show that seismological and geologic factors, relating to the generation and transmission of the seismic wa ves, could explain the unusually weak base excitation in Kirovakan. Th en, the results of one-dimensional (1D) wave-propagation analysis, usi ng soil profiles with field and laboratory measured parameters, are pr esented 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 consi st of less than 30 m dense gravelly sands and stiff clays. However, su ch analyses fail to explain the disproportionately large degree of dam age observed only in one region, where soil profile constitutes a tria ngular sedimentary basin with maximum soil depth of about 150 m and wi dth-to-depth ratio of about 5. A simplified three-dimensional wave-pro pagation analysis of the ''valley'' effects on ground-surface motions, provides a better explanation of the observed damage.