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Figure11.Measurementsof shorewardwavepropagationofGreatEast Japan
tsunamiatcoastalGPSwavebuoysdeployedbythePortandHarbourBureauof
theJapaneseMinistryofLand,InfrastructureTransport,andTourism(Adapted
fromTakahashi2011)
Figure 11 shows the location and wave records at the five buoys closest to the
Tohoku coast. The highest wave records occurred at Kamaishi and Miyako, with the
Kamaishi buoy registering an offshore wave height of 6.7 m, 26 minutes after the
main shock of the earthquake and 6 minutes before the first waves made landfall.
This buoy lies 18 kilometers offshore in a water depth of 204 meters (Takahashi
2011). From these records, tsunami waves apparently lasted around 45 minutes,
although the number of distinct waves observed at the shoreline remains unclear.
As discussed above, the epicenter for the Great East Japan event was located off the
Oshika (Ishinomaki) peninsula with maximum terrestrial displacements recorded at
the same latitude (Figure 9). Preliminary estimates of the slip region at the seismic
source below the sea floor are consistently to the south and east of the epicenter (see
Figure 10). The maximum tsunami amplitudes and runups, however, are north of the
epicenter, with the highest runup of over 40 m near Yamada in Iwate prefecture about
180 km north by northwest of the epicenter. These high runups are consistent with the
observations reported by Sato (2011) in Figure 9 which show larger offshore sea bed
displacements north of the epicenter. The differences between displacements at 32
km depth and at the sea floor highlight difficulties in predicting tsunami behavior
using only seismic information.
 
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