THE RELATIONSHIP BETWEEN STRENGTH AND SEISMIC PROPERTIES OF PERMAFROST

About ۵۰% of the territories of seismoactive regions of Russia account for areas of permafrost distribution. The ways of assessment of seismic hazard of grounds, elaborated for regions with a positive geothermal fields, can not be applied to the territories of permafrost. It is primarily due to the instability of seismic properties of permafrost within a year. Near the surface frozen grounds periodically transfer to a thawed state and back to a frozen one. A frozen ground is generally considered as four-component system which consists of a mineral ice skeleton, unfrozen water, and aqueous and gas vapors. It should be noted that within elastic motions frozen grounds with -۲۴C and lower do not differ from rocky grounds in velocities of seismic wave propagation and amplitudes of motions. But at strong seismic effects they differ from rocky grounds due to their different strength properties. That is why both strength and seismic ground properties should be considered at assessment of seismic hazard of permafrost.