Environmental Engineering Reference
In-Depth Information
the error margin can be useful for adjusting the design height or determining the
range of acceptable risk to address limitations of the technology in reducing the
impacts of future disasters.
Based on the above numerical results, the area from the coast to the elevated
prefectural road should not be resettled. Although the multiple barriers reduce the
effects of the M 7 class earthquakes, which are likely to occur more frequently off
the Miyagi (Sendai) coast, the inundations generated by the M 8 and M 9 class
earthquakes can be amplifi ed by the existence of barriers and thus increase the risks.
For the area between the prefectural road and the Tohoku expressway, our
numerical simulations indicated that 40 % of the 14 total scenarios of M 8 and M 9
class earthquakes could still affect this area with maximum and average simulated
tsunami fl ow depths of 4.3 m and 2 m, respectively. As highlighted through the
developed fragility curves for Miyagi Prefecture by Koshimura et al. (
2013
), this
area may still be used for non-residential activities, including factories with rein-
forced concrete buildings.
The above observations are consistent with the decisions made by the Sendai
City Government. The area between the coastline and the elevated prefectural road
has been declared a tsunami Level 1 area, where no resettlement is allowed. The
area between the prefectural road and the maximum tsunami inundation from the
2011 event has been declared a tsunami Level 2 area. This new zoning policy has
now been applied to the reconstruction and in the offi cial tsunami evacuation plan
in Sendai City (Fig.
10.10
).
10.3.3
Model Application in the Pre-disaster Area
In Owase City, only 64 of the total 137 simulated tsunamis generated inunda-
tions. Among those, the 13 cases that reached the maximum inundation distance
originated from earthquakes with magnitudes larger than 9.0 Mw. Similar to
Sendai, earthquakes with magnitude 9.0 Mw have never been recorded in the
past. The historical fl ow-depth data in Owase City indicate a maximum value of
4 m, which has been correlated with M 8 class earthquakes in the past. Our
modeling results from M 8 class earthquakes were consistent with these histori-
cal data. By taking the median of the simulated fl ow depths, the modeling results
can fairly accurately reproduce the historical tsunami fl ow depths in Owase City
(Fig.
10.11
).
We include the results of the M 9 class earthquakes for comparison in Fig.
10.11
.
Here, we can see a signifi cant discrepancy between the historical records and the
potential maximum tsunami fl ow depths that may occur in the future. This condition
is similar to the situation in Sendai prior to the 2011 tsunami event. There were no
records above 5 m available in the historical data when the old hazard map of the
Sendai plain was developed. Based on the 2011 tsunami, therefore, the results of the
present study are fundamental to updating the existing hazard maps and the
evacuation plan in Owase City.
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