Saturday, March 12, 2011

During The Big One

5 PM, Sunday 13 March, local time.
Two days ago, around this time, we at Hokkaido University's Institute of Seismology and Volcanology in Sapporo, Japan, were all glued to the TV, watching the tsunami roll in to southern and eastern Hokkaido, as the sun was setting.

About two hours earlier, I had been sitting at my desk/computer when the room started to move. I knew it was an earthquake. There had been one two days before, a 7.2, off the Sendai coast of northern Honshu--an earthquake I didn't feel, but others in Sapporo did, including Olga, who on the 11th floor of her building was scared. By THAT one. We did not know, nobody knew, what was to come.

On 11 March at around 2:45 PM local time, I wrote on my Facebook page:
earthquake right here right now

It was moderate motion, and it kept going, with some increase and decrease in the degree of shaking/rocking. After some time, I started to look at my watch -- how long could it last? I felt like I was on a ship, and the Earth was the ocean. I started to get seasick. Finally it petered off, though the blinds kept swaying. I wrote:
ok, the building just shook for over two minutes, i am just fine, a little motion sick,
actually--the motion seemed to kind of circular and rocking. curtain rods still moving

Then I went out in the hallway to find out what was what. A colleague there said "big earthquake" -- yes, big, but of course I wanted to know HOW big. Having never experienced a big earthquake (my maximum was 5.6 near San Jose, CA), I hadn't an internal gauge, but I did know that long-duration shaking characterizes big earthquakes. I went to the USGS website to see if the earthquake was registered -- it was, with a preliminary magnitude of... 7.9 off northern Honshu, same area as the 7.2 on 9 March, a location which I'd expected. Actually, though, I suppose I was expecting a larger magnitude given the duration of shaking, but I had no real basis for doubt. In any case, both my colleagues in the Institute and also the Tsunami Bulletin Board were mentioning tsunami. I wrote into Facebook:
It's a 7.9 off northern Honshu, there is a big tsunami warning, but don't worry, I am not in danger.

Well, 7.9's can make decent tsunamis, sure there would be some runup on the Sendai coast and surrounding region. I watched the TV with my colleagues, I could understand neither the speech nor the printed words, except for numbers, such as 6 m [maximum runup], and the map with four zones of warning -- red/white for maximum, red for intermediate, yellow for ... [I am not sure actually, of numbers], and clear for no danger. Sapporo was in the clear.

Then the videos started to come in. The first ones were not too dramatic, as we watched water rising against docks and seawalls. Pretty quickly, though, the maximum projections were up to 10 m, and the red-and-white most dangerous zone extended significantly. Cars and trucks in floating in the water were starting to tip over the tops of seawalls and even eroding them.

There were many felt aftershocks--why were we feeling aftershocks from a 7.9, when I didn't feel the 7.2? Two aftershocks got recorded in real time on my Facebook [I was running back and forth between my computer and the TV/situation room]:
3:11 --aftershock, more shaking right now
3:28 -- another aftershock, more as I've been watching live TV of the tsunami coming in to Miyagi prefecture, where we were on a tsunami field trip last year; it's a big tsunami, strong currents running through town; ok, a BIG aftershock right now!!!

I didn't have my camera in the TV room to begin with, I brought it in later. I am not sure I wrote the following before or after the first picture I took of the screen:

3:48 --
The tsunami runup projections are increased to 10 m in places, and all of Japan is on alert. I haven't seen the projections yet for Hawaii, it will take some hours to get there, but the tsunami bulletin board [I am on it] should be posting projections, I am not sure why they are quiet.

This is the tsunami coming in over the Sendai plain. The tsunami looked kind of sluggish and is full of vegetative debris here. It is carrying fires along with it! You can see that buildings are pretty much intact, despite the huge earthquake that had preceeded this.

If there is a time on the TV screen, it's in Japanese. I interpreted the runup numbers [in meters] to be measured, rather than predicted, because the predictions were in whole numbers.

The map at the lower right shows the levels of warning for all of Japan's coa stlines. It's hard to see the details, but by this time, the white/red zone had been expanded.

Why did the tsunami look so sluggish, rather like lava or a debris flow? I began to think of the setting, where I had been the previous April. There was a seawall along the coast, and a pine forest between the seawall and the many rice fields. The tsunami must have piled up on the sea-side of the seawall and now was pouring over, feeding a rather steady advance across the plain. It was so strange and compelling to see it in real time on the TV. Sometimes I wanted to yell at people when they seemed not to be making good decisions [get out of your car and run!].

The forecasts of tsunami size had been increased, and so had the earthquake amplitude. I didn't realize this at first -- in fact, the estimated earthquake size in Japan might always have been larger than 7.9, but here it is on the screen, around the same time our colleague Yoshinobu Tsuji appeared to comment on the unfolding events.

The tsunami hasn't advanced onto these fields yet, but you can see that the earthquake magnitude is up to 8.4.

My next Facebook entry was at 4:58:
The tsunami is arriving on Hokkaido. There is news of earthquake damage and some casualties. Tsunami videos mostly show strong currents carrying boats and cars, in some cases right over sea walls...

After this, most of my photos for awhile are shots of the tsunami wave behavior. Also some shots of the drowned Sendai airport. People were [safely] up on the roof of the building.

Someone in the seismology group brought in a printout of records from a station at Tarumai volcano, not far from Sapporo. The top diagrams are a strainmeter record, the lower diagrams are records from a three component seismograph [vertical, e-w, n-s]. The records are clipped because the seismograph was calibrated to measure smaller events. A bit later, we saw the record from a tiltmeter of the mainshock and two aftershocks.

I can't go on right now, I just looked at these images, and I am stunned and very sad:

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