Based on the data of the Kokubunji (Tokyo) ground-based vertical sounding station of the ionosphere (1957–2020), hourly variations in the critical frequency foF2 were studied in connection with earthquakes. Using the epoch superimposition method for M6.0 + earthquakes at depths H < 70 km and distances up to 2000 km, a statistically significant increase in the mean foF2 value 1–8 days before, and a significant decrease 1–8 days after, earthquakes were detected. These disturbances took place at distances up to 1500 km. The average amplitude of the effects is about 1–1.5%. There is no significant difference in the manifestation of effects during night and day time. For shallow earthquakes (H < 35 km), the increase in amplitude was the greatest at distances Rd < R < 3Rd, where Rd is the Dobrovolsky radius Rd = exp(M); for events with depths of 35 ≤ H < 70 km, ionospheric effects are reliably distinguished only up to the Dobrovolsky radius.