We calculate the effects of the pair production of top quarks and their subsequent weak decays on event topologies and inclusive distributions in e +e - annihilation experiments. The resulting jet distributions are compared with those originating from the lighter quarks (u, d, s, c, b) with higher-order QCD corrections included. The calculation is based on the Kobayashi-Maskawa model for the weak decay of the heavy quarks including non-leptonic and semileptonic decay modes. The final evolution of quarks into hadrons has been taken into account using a quark fragmentation model. We find that the jet measures such as sphericity, thrust and acoplanarity are very sensitive to the onset of a new quark threshold in e +e - experiments. A comparison is made with available data from PETRA in the energy range 13 ⩽ Ecm ⩽ 31.6 GeV in order to test the model below the toverlinet production threshold.