Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, Japan

LIQUEFACTION DAMAGE OF THE TONEGAWABASIN CAUSED BY THE 2011 OFF THE PACIFIC
COAST OF TOHOKU EARTHQUAKE
Shigeki SENNA1 , Nobusuke HASEGAWA2 , Takahiro MAEDA3, Hiroyuki FUJIWARA4
1Researcher, National Research Institute for Earth Science and Disaster Prevention,
Tsukuba, Japan, senna@bosai.go.jp
2Researcher, National Research Institute for Earth Science and Disaster Prevention,
Tsukuba, Japan, nobusuke-hasegawa@bosai.go.jp
3Researcher, National Research Institute for Earth Science and Disaster Prevention,Tsukuba, Japan, tmaeda@bosai.go.jp
4Project Director, National Research Institute for Earth Science and Disaster Prevention,
Tsukuba, Japan, fujiwara@bosai.go.jp

ABSTRACT: By the 2011 off the Pacific coast of Tohoku Earthquake, a large number of liquefaction
occurred in the Tone river basin. By this liquefaction, serious damage including the cutoff of thelifeline, the destruction of the house basics and the nonequivalent subsidence occurred. Theliquefaction damage taken up by the news was a small portion. Then we carried out a local survey forthe purpose of catching perspective of the liquefaction damage in the Tone river basin. It was almost
the artificial ground where filled up pond and river that intense liquefaction was seen. The groundhazard by liquidizing was known from of old. It was recognized again to cause an extensive groundhazard by liquidizing in this earthquake. It is thought that liquidizing is generated by the earthquake inthe future again. Next, we compared our data with the liquefaction locations, the geomorphologic
classification of the regions, seismic intensity distribution, and liquefaction probability value in the Kantodistrict in the report published by the Committee for Analysis of Liquefaction in the off the Pacific coast of
Tohoku Earthquake, chaired by the author and organized by the Ministry of Land, Infrastructure, Transportand Tourism. It was calculated by the method of judging the liquefaction studied until now.
Furthermore, the long continuation time of the earthquake ground motion which is the feature of thisearthquake investigated the influence which causes liquefaction. Moreover, about the HINODE area in
Itako city whose liquefaction damage was serious, creation of a detailed structure model andmicrotremor observation were performed. The scale of liquefaction was harmonic when the structure
model of this study was compared with the damage report information on a city office.
Key Words: Liquefaction damage, The Tonegawa basin, Artificial ground, residential land,secondary disaster, Liquefaction probability, Microtremor observation

INTRODUCTION
The off the Pacific coast of Tohoku Earthquake that occurred on March 11, 2011, caused liquefaction
damage over an extremely large region extending from the Tohoku district to Kanto district. However, thedetails of the liquefaction damage have not yet been fully clarified, even though half a year has passed719

since the outbreak of the earthquake.
This is because initially, survey of the damage was greatly delayed owing to planned power outage andgasoline shortage and also because the damaged areas were spread extensively. The region damaged byliquefaction was spread across five prefectures in the Tohoku district (Miyagi, Fukushima, Aomori,
Yamagata and Iwate Prefectures), six prefectures in the Kanto district (Tochigi, Gunma, Ibaraki, Saitama,Chiba, and Kanagawa Prefectures), and the Tokyo Metropolitan area according to survey information
released by academic societies, information on the municipality websites, and our field survey. (Fig. 1)

Assumption fault
Suzuki et al.(2011)

Fig.2 Area

Fig. 1 The distribution of seismic intensities(JMA) in the municipalities that suffered liquefaction
damage in the 2011 off the Pacific coast of Tohoku Earthquake
In the Tohoku district, regions other than four prefectures mentioned above, liquefaction occurred inlowlands and in reclaimed lands in the areas for which a seismic intensity higher than 5 was recorded. Of
the prefectures in the Kanto district, Chiba and Ibaraki Prefectures recorded a large number of cases ofliquefaction damage. As will be described later, liquefaction occurred over a very wide region with highdensity mainly in the reclaimed lands in these two prefectures. (See Fig. 2) However, liquefaction occurred720

in fewer locations in Miyagi Prefecture, which is located near the epicenter of the main earthquake, than in
the Kanto district. This could be because the tsunami that attacked the coast of Miyagi Prefecture removedall traces of liquefaction damage, or because the Sendai Plain has a smaller area of lowland created by
alluviation by big rivers and reclaimed land. We discuss the liquefaction damage in 28 municipalities
mainly in the Tonegawa basin (including the Pacific coast and the basins the subsidiary streams ofTonegawa) in the Kanto district that reported a very large number of liquefaction damage cases.

SUMMARY OF THE FIELD RESEARCH
We conducted field research for two days, on April 7 and 8, 2011. Figure 1 shows the 28 municipalities,
all of which are in Ibaraki Prefecture, covered in the field survey. These municipalities are located in thebasins of the Tonegawa and its subsidiary steams Kinugawa and Kokaikawa; the field survey also includes
Kashima City and Namegata City, both of which are on the coast of Kitaura Lake, which is part ofKasumigaura Lake. Because of the limits of the survey schedule, we did not cover Inashiki City in Ibaraki
Prefecture in the Tonegawa basin or Noda City in Chiba Prefecture. We tried to capture the locations andscale of liquefaction as exhaustively as possible. After collecting information on the sites of liquefaction
from each municipality office, we conducted the field survey. Hence, we did not conduct the field survey in
two municipalities (Moriya City and Narita City) for which we did not have any information onliquefaction by the time we started the field survey.The following three groups conducted the field survey.

Fig. 2 Distribution map of liquefaction locations and photographs showing liquefaction damage
in the Kanto district (Information on the liquefaction points and areas was provided by theCommittee for Analysis of Liquefaction in the off the Pacific coast of Tohoku Earthquake)721

① Downstream basin ofTonegawa (including the Pacificcoast)

ForestPaddy field
Field
Tea garden
Shrub
Wasteland

Fig. 3 Meiji era (left) and present (right) topographic maps of the region near Hinode in Itako City

ForestPaddy field
Field
Tea garden
Shrub
Wasteland

Fig. 4 Meiji era (left) and present (right) topographic maps of the region near Sawara in Katori City

Photo 1 A large volume of sand boil wasobserved, and many telephone poles becameslanted. The telephone pole standing straight wasinstalled after the earthquake. (Hinode, Itako)

Photo 2 The ground in front of Katori
Health Center subsided, and a depressionof about 50 cm was created. (Sawara,Katori)722

② Midstream basin of Tonegawa

ForestPaddy field
Field
Tea garden
Shrub
Wasteland

Fig. 5 Meiji era (left) and present (right) topographic maps of the region near Fusa in Abiko City

ForestPaddy field
Field
Tea garden
Shrub
Wasteland

Fig. 6 Meiji era (left) and present (right) topographic maps of the Iwai Greenland in Bando City

Photo 3 Large-scale liquefaction occurred,and many telephone poles became slanted.
(Fusa, Abiko)

Photo 4 Traces of sand boils spreading on theroad (Iwai Greenland, Bando)723

③ Basins of Kinugawa andKokaigawa

ForestPaddy field
Field
Tea garden
Shrub
Wasteland

Fig. 7 Meiji era (left) and present (right) topographic maps of the region near Yoshino in Joso City

ForestPaddy field
Field
Tea garden
Shrub
Wasteland

Fig. 8 Meiji era (left) and present (right) topographic maps of the region near Chiyogawa in
Shimotsuma City

Photo 5 Sand boils and subsidence(Yoshino, Joso)

Photo 6 Sand boils occurred over a widearea. (Chiyogawa, Shimotsuma)

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THE SUMMARY OF ANALYSIS RESULTS
Because the data we collected on the liquefaction locations cover only part of the Tonegawa basin, as
shown in Fig. 2, we compared our data with the liquefaction locations, the geomorphologic classification ofthe regions, seismic intensity distribution, and liquefaction probability value in the Kanto district in thereport4) published by the Committee for Analysis of Liquefaction in the off the Pacific coast of Tohoku
Earthquake, chaired by the author and organized by the Ministry of Land, Infrastructure, Transport andTourism. We have indicated the liquefaction locations as points on the aerial photograph of the Kanto
district showing Chiba and Ibaraki Prefectures in Fig. 9. Similarly, we show on a background map, thegeomorphologic classification provided by Wakamatsu, et al. (2005)5) in Fig. 10 and the distribution of
estimated surface seismic intensities in Fig. 11. The liquefaction probability values calculated by Matsuokaet al. (2011)6) are shown in Fig. 12.

Figure 9 Distribution of liquefaction
locations in the Kanto district

Figure 10 The liquefaction locations in Kantodistrict and geomorphologic classification ofthe region
To study the distribution of estimated seismic intensities on the ground surface, we considered theinstrumental seismic intensity; thus, a significant amount of the instrumental seismic intensity data canbe obtained from many seismometers, as proposed by Matsuoka et al. (2011)6). First, we calculated theinstrumental seismic intensity from the observational data of strong earthquake motions. However, because
this data reflects the S-wave velocity that corresponds to the location of the seismometer, we have to isolatethe contribution of the ease with which seismic waves travel through the surface, and eliminate it from theprobability values. We calculated the degree of amplification of the instrumental seismic intensities byconsidering the average S-wave velocity (Vs30)7) in the ground; the velocity data are available from the725

Fig. 11 Liquefaction locations and seismic
intensity distribution in the Kanto district

Fig. 12 Liquefaction locations and probability
distribution of liquefaction (from Matsuoka, etal. (2011))
250 m mesh map showing the geography and ground classification. We estimated the instrumental
seismic intensities on the hard ground (Vs30 = 600 m/s). Thereafter, we calculated the distribution ofseismic intensities on the ground surface using the Simple Kriging interpolation9) that uses the distancedecay formula for the epicenter8) as the trend component; we obtained the distribution map of instrumental
seismic intensities on the ground surface by adding the amplification degrees to each 250m cell of the mesh(Figure 11). For the calculations, we used the records of K-NET and Kik-net of National Research Institutefor Earth Science and Disaster Prevention (NIED) and the seismometer records obtained from themunicipalities. Liquefaction damage is mostly observed in locations on the land reclaimed from old river
channels and lakes. In the inland area, liquefaction damage occurred in many areas that experienced aseismic intensity of 5-upper as well as in the areas that experienced a seismic intensity of 5-lower.
Table 1 shows the correspondence relationship between geomorphologic classification and liquefaction
locations that are listed. Figure 13 shows the percentage of liquefaction events in locations classified
according to geography and ground types. This figure shows that most liquefaction events, i.e., about 35%
occurred in the reclaimed land, followed about 16% each in delta and coast lowland, and about 8% inbackswamps. The geomorphologic classification of the Kanto district shows that the percentage ofliquefaction events is the highest, i.e., about 20% in reclaimed land. This is followed by old river channels
where about 10% of the liquefaction events occurred and drained land where about 7% of the liquefaction
events occurred; this indicates that liquefaction occurred in artificially altered lands and low marshlands.
Figure shows the comparison of the probability values obtained from the intensity distribution shown in
Fig. 11 by using the relational formula developed by Matsuoka, et al. (2011) 6); Table 2 lists the detailed
results.

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Table 1 Relationship between the liquefaction locations in the 250 m mesh and thegeomorphologic classification

Fig. 13 Percentage of liquefaction events in locations classified according to geography and ground types

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Table 2 Probability distribution of liquefaction events according to geomorphologic type of land andthe average probability values ( matsuoka et al.(2011) ).

Fig. 14 Probability distribution of liquefaction events according to geomorphologic type of land and theaverage probability values ( matsuoka et al.(2011) ).

Table 2 lists and Fig.14 figure the calculation results of the average probability of liquefaction. From thelist, it is seen that the reclaimed land has the highest liquefaction probability of 1.73%, followed by oldriver channel with a probability of 1.63%, and drained land with a probability of 1.51%. These probabilities
agree with the ranking of liquefaction in the entire Kanto district listed in Table 1. The method used byMatsuoka et. al (2011) reflects the extensive distribution of the liquefaction phenomena very faithfully.

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IBR017 EDOSAKI
EW

NSUD

CHB024INAGE

IBR014 TSUCHIURA

EW

EW

NSNS

UD

UD

Fig. 15 NIED observation points for the 2011 off the Pacific coast of Tohoku Earthquake. Solid
red circles indicate the locations where liquefaction occurred, while solid black circles indicate
the locations where liquefaction did not occur (A waveform is an acceleration(gal))

CONCLUSIONS
We summarize the relationship between the occurrence of liquefaction and geomorphology, as observed
from our research on three regions, namely, the Pacific coast of the Kanto district, downstream basin
Tonegawa, and midstream basin of Tonegawa.
(1) The Pacific coast of the Kanto district (Kamisu City, Kashima City, and Choshi City)
Severe liquefaction was observed not only in lands artificially reclaimed from gravel plants and ponds
but also in natural lands such as dunes.
(2) The downstream basin of Tonegawa (Itako City, Namegata City, Tohnosho town, Katori City, Kozaki
town, Kawachi town, and Tone town)
In this area, liquefaction mainly occurred in artificial lands reclaimed from ponds and rivers.
Liquefaction may have occurred in natural grounds such as valley lowlands and backswamps. However,liquefaction in the artificial lands was so severe that no municipal office in this area received reports onliquefaction in the natural lands in this area.” Please revise the highlighted text suitably.
(3) Midstream basin of Tonegawa (Municipalities other than those mentioned above)
Nearly all of the severe liquefaction events occurred in the artificial lands reclaimed from ponds andrivers. Liquefaction was also observed in natural grounds (the geomorphological types being natural levees,
valley lowlands, sandbanks, and gravel sandbanks). However, most areas where liquefaction occurred are
paddies in terms of land use, and these are catchment areas such as narrow valleys geographically.
By interviewing residents, we learnt that severe sand boils occurred during the aftershock at 15:15 thanduring the main earthquake at 14:46 on March 11 in the eastern regions of Ibaraki and Chiba Prefectures,729

along the Pacific coast; this includes Itako City, Kamisu City, Kashima City, and Kozaki City. This suggests
the possibility that the maximum acceleration was relatively high along the Pacific coast in Ibaraki andChiba Prefectures near the point of the aftershock and that the excessive interstitial water unreleased during
seismic motions in short intervals that created a great earthquake worsened the liquefaction damage there.

ACKNOWLEDGMENTS
We express our sincere gratitude to Shohei Naito, Asako Iwaki, Ken Xiansheng Hao, Nobuyuki
Morikawa, and Shinichi Kawai of National Research Institute for Science and Disaster Prevention (NIED)
for their support during the field survey. We used earthquake and ground data from K-NET and Kik-net ofNIED. We also extend our thanks to Professor Kazue Wakamatsu of Social Environment Department ofCollege of Engineering of Kanto Gakuin University for the information on past cases of liquefaction
damage.

REFERENCES
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