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Aanomalous features of the defects in Si implanted amorphous SiO2 are reported. The numbers of E'1 centers and B2 centers are found to increase monotonically with implanted Si dose, in contrast to the saturating feature of these numbers in Ar implanted samples. Moreover, when H ions are implanted in amorphous SiO2 predamaged by Si implantation, both of the density and the number of E'1 centers increase and they reach a constant value at a small H dose. We point out that these anomalies can be explained in terms of the difference in the cross-section for defect annihilation in the specimens implanted with Si ions and other ions, in accordance with the homogeneous model proposed by Devine and Golanski. We consider that the main mechanism of defect annihilation is the recombination of an E1 center and an interstitial O, which is stabilized by an implanted Si, reducing the cross-section in Si-implanted specimens.