At Fukushima Daiichi and Daini tsunami waves went over seawalls and destroyed diesel backup power systems. This loss of power caused severe problems including two large explosions at Fukushima Daiichi and leakage of radiation. Over 200,000 people have been evacuated. Seismic recordings at six assessed nuclear power plant facilities indicated the plants had been exposed to "peak ground accelerations" of 0.037–0.383 "g" and "peak ground velocities" of 6.18–52.62 cm/sec.