The whole and aftershock-depleted shallow (depth ≤30 km) seismicity of Taiwan from 1990 to 2017 was investigated by using fractal and spectral methods. The global and local coefficient of variation and the Allan Factor showed that the time distribution of both the whole and aftershock-depleted seismic catalogues are characterized by time-clustering structures. In particular, at small timescales the seismicity of the whole and aftershock-depleted catalogues can be represented as a Poisson process. Persistent time fluctuations have been identified in the interevent time series, while weak persistence or randomness in the magnitude series. By applying the singular spectrum analysis to the daily number of events of the aftershock-depleted catalogue, quasi-monthly and bi-weekly periodicities were revealed. Furthermore, the correlation between the Taiwanese seismic activity and Earth’s tides was suggested by the appearance of quasi-annual and quasi-semestral periodicities.