Existing earthquake resistive design methods of trench type tunnels can be classified into two; the design method by design spectra and the response analysis by electric computer. This paper discusses the concept of the design method by using spectra and proposes design spectra requried.
　49 components of strong motion earthquake records of which the maximum accelerations are greater than 50 gal., out of those gathered by the observation network of the Earthquake Resistant Structures Lab., were treated. Relation between period and displacement amplitude of the equivalent sinusoidal waves were computed by the electric computer for each record. Then, at 1st, those were classified into three groups, that is, A, B and C, from ground conditions at each observation station point of view. The 2nd the other classification in which the magnitude of each earthquake were taken into consideration, that is, A, B' and C' was tentatively proposed.