The object of the investigations is seismic input models used in structure designing under the conditions of limited seismological information. The aim of the given investigation is to propose a new variant of a seismic input model, which should be generated for the structure under consideration, taking into account main peculiarities of actual seismic excitations. The method of design seismic input generation by means of its presentation as a sum of velocity impulse and multi frequency excitation has been developed. The duration and peak value are parameters of velocity impulse. They can be presented as function of possible earthquake magnitude and hypocentral distance. Multi frequency excitation can be presented as a product of sinusoid and some envelope function. Parameters of the impulse and multi frequency excitation are determined to provide accordance of generated input characteristics with characteristics of past earthquakes. Characteristics of past earthquakes were estimated using the joined database including more than 100 records of strong earthquakes presented by Chinese and Russian experts.