Background and Scope - Tohoku, Japan Earthquake and Tsunami of 2011 - page 7

seismic source. The pressure wave arrival is seen clearly after an elapsed time of 45
seconds; the shear wave maximum is seems after an elapse time of 95 seconds. The
acceleration of 2.7 g at this gauge was the maximum recorded by instruments for this
event.
Figure 2. North-South acceleration record in Miyagi prefecture showing the
maximum recorded acceleration of 2.7 times the earth's gravity (Kyoshin-Net 2011)
1.3.3SequenceofWarningandDisasterResponse
The Great East Japan event, which began with the seismic rupture on the afternoon of
March 11, evolved quickly over the following hours: aftershocks and shaking effects
continued, a series of tsunami waves propagated onshore, and the ensuing damage
initiated a nuclear disaster at two power plant facilities in the Fukushima prefecture.
The tsunami waves also propagated across the Pacific Ocean, affecting coastal
communities throughout the Pacific and in North and South America. Table 2a and
Table 2b present a summary timeline of some of the main aspects of the disaster
along with some of the warning and response activities undertaken to mitigate
damage and casualties. In the tables, highlighted cells signify activities related to the
earthquake (green cells), tsunamis (blue cells), and nuclear response (pink cells).
Tables 2a and 2b also illustrate the broadening focus of emergency responders as
each additional part of this disaster occurred.
The JMA issued the Earthquake Early Warning 31 seconds after the start of the main
shock. Slightly over two and a half minutes elapsed between the time of the first
shock and the Major Tsunami Warning, which JMA issued at 5:49 UTC. JMA based
its warning on an initial earthquake magnitude estimate of 7.9 and predicted waves in
excess of three meters in three prefectures: Iwate, Miyagi, and Fukushima. After nine
minutes, JMA, in its capacity as the North West Pacific Tsunami Advisory Center,
also issued expected tsunami heights for areas of the western Pacific and Indonesia.