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The Tohoku earthquake, March 11 2011

It was the third earthquake of the week, and at first, seemed no larger.  Earlier in the week we had been rattled by a 7.4 earthquake far to the north along the Japan trench.  In the JAMSTEC cafeteria we watched the tsunami warning issued by JMA along the Japanese Pacific coast.  Early the next morning, an other smaller but closer earthquake shook me awake ~ 6:30 am.  So the Sendai earthquake was the third of the week.  When it happened, about 40 of us were in a workshop for those involved in studying the Sumatran earthquakes of 2004-2010.  My first thought was that it might interrupt the workshop, and it was Friday afternoon just before 3:00, so not much time left for an interruption.  But instead of stopping at a few seconds, or maybe a minute as the earlier ones had, this one kept going, and going, and going.   In a room full of seismologists, we timed the gap between the P-wave and S-wave arrivals, and then started thinking about whether we should get out of the building.  The desks looked really flimsy, so duck and cover didn’t look good at all.  On the other hand, were were possibly in one of the safest buildings in Tokyo (NE outskirts in Kashiwa-Chiba).  The corners of the room had pillars at least a meter square, and looked really solid.  But we went outside anyway.  It’s amazing how much you can do in five minutes.  After about a minute of shaking, were were all outside in the courtyard, watching the flagpole on the roof of the 7th floor whipping through 60 degrees, and the dry rattle of the trees with last years leaves as they shook.   Since we were all there, we snapped a quick group picture during the quake.

The mainshock lasted 5-6 minutes, an eternity.  Then we felt strongly the very large aftershock that felt (and turned out it was) very close to our location.   I never realized you could feel the difference between the different types of waves; The P-wave is like a jackhammer under your feet, the S wave much more like an ocean wave.  We all felt a little seasick as the S waves went on for many minutes.   A few minutes later, we all watched the first wave of the tsunami arrive in Miyako on live streaming video on Kenji Hirata’s cell phone, while the ground was shaking.

Studying earthquakes in one thing, but riding through a great earthquake was different.   The aftershocks were nearly continuous for the next 12 hours or more.    It’s a long time for the earth to feel like the ocean.    Two days later, the wingtips of the airplane bounced up and down on the ramp with more aftershocks just before leaving for home.  Nothing more useless than an earthquake geologist just after a a huge earthquake, so we all flew out,and our Japanese colleagues of course stayed to deal with a new reality in Japan.  The attention had to turn to rescue and recovery, and our work will come later.

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Written by eqgold

March 22, 2011 at 6:01 am

Posted in Uncategorized

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