Fukushima Diary reports of tweets from Fukushima residents that claim to feel the recent earthquakes (all very near the surface) as different, as if they were explosions:
I think everyone has noticed it if they live in Fukushima since 311, and paid attention to earthquakes. Suddenly, the way of shaking has changed, isn’t it ? feels like something is exploding underground, like a bomb.
I feel that too. It feels as if I was sleeping in the double bunk beds and someone knocked me up from the lower bunk. It comes up from the underground all of a sudden, like bang. I woke up several times to be surprised at the knocking up shock. My heart beats heard, can’t be reassured for around the clock.
I live in Ibaraki, but my family, and people around me feel the same way too. It’s not a normal earthquake, but a short quake as if something was exploding underground. I haven’t felt that quake for 40 years. It happens everyday.
A hydrovolcanic explosion or series of them would be the result of a China syndrome, an uncontrolled nuclear meltdown in which the corium penetrates the ground and eventually reaches the water table, than in Fukushima, which is by the seaside, must not be deep underground.
In Chernobyl they dug a mine under the reactor and froze the soil under it, while also cooling the corium with tons of sand and filling the holes in the vessel with lead. In Fukushima, as far as we know, nothing of this has been even tried and the China syndrome has gone all the way without remarkable disruption.
Mochizuki contends however that:
The only reason to deny the possibility of hydrovolcanic explosion underground is because the radiation level is not spiking up after the earthquake, but I doubt if the steam comes right above the epicenter.
Update (Jan 13): Ex-SKF mentions an opposition councilor (upper house member) claiming that there was an explosion in Fukushima on this day (Jan 9), probably at reactor no. 4. Fukushima Diary also echoes this.