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

RECURRENT LIQUEFACTION INDUCED BY THE
2011 GREAT EAST JAPAN EARTHQUAKECOMPARED WITH THE 1987 EARTHQUAKE
Kazue WAKAMATSU1
1

Professor, Department of Civil and Environmental Engineering, Kanto Gakuin University
Yokohama, Japan, wakamatu@kanto-gakuin.ac.jp

ABSTRACT: The Mw 9.0 destructive earthquake that occurred March 11, 2011, in Japan
was associated with widespread liquefaction within a 500-km long zone that extended
from Iwate to Kanagawa Prefectures in the eastern part of Japan. Based onreconnaissance surveys of the Great East Japan Earthquake of March 11, 2011,
recurrence of liquefaction at the same sites was identified at sites where liquefaction had
occurred during the MJ6.7 Chibaken Toho-oki earthquake of December 17, 1987; thesurveys also compared observed liquefaction effects with those of the 1987 earthquake.
Key Words: Great East Japan earthquake, liquefaction, re-liquefaction, 1987 Chibaken
Toho-oki earthquake

INTRODUCTION
Liquefaction has been known to occur repeatedly at the same site during successive earthquakes,
as shown by examples from Japan, United States, and Greece (e.g. Kuribayashi and Tatsuoka, 1975;
Youd and Hoose, 1978; Youd and Wieczorek, 1982; Suga et al., 1983; Yasuda and Tohno, 1988;
Papathanssiou et al., 2005; Wakamatsu, 2011; and Yamada et al., 2011).
Wakamatsu (2011) revealed that recurrence of liquefaction at the same site had occurred at 150
sites, including the re-liquefaction sites identified by Yasuda and Tohno (1988) based on the GIS
database analysis for approximately 16,800 liquefied sites during the period from 745 to 2008
throughout Japan. These repeated liquefactions were concentrated in areas with specificgeomorphologic conditions: abandoned river channels (36 sites) artificial fills (35 sites), and lower
slopes of sand dunes (26 sites).
Widespread liquefaction was generated repeatedly in natural sediments within a short period in
Christchurch and adjacent areas, New Zealand, during the September 2010 Darfield (Mw 7.1),
February 2010 Christchurch (Mw 6.2), and 13 June 2011 Christchurch (Mw 6.2) earthquakes, causing
significant damage to residential buildings and lifelines (Yamada et al., 2011). The repeatedliquefaction was often quite severe, and many residents reported that in some cases the severity
increased in subsequent events.
It is important for evaluating the process of re-liquefaction and the aging effects of soils againstliquefaction to investigate instances of repeated liquefaction. In addition, the locations of repeatedliquefaction are considered potential areas of liquefaction in future earthquakes. In this study, the675

author collected more than 60 instances of repeated liquefaction at sites where liquefaction was
induced by the March 11, 2011, Great East Japan Earthquake, and compares observed liquefaction
effects with those associated with a previous earthquake. The land-use history, geomorphology, andgeotechnical conditions of the sites are also examined.

DISTRIBUTION OF LIQUEFIED SITES CAUSED BY THE 2011 GREAT EAST JAPAN
EARTHQUAKEAt 14:46 local time on March 11, 2011, a gigantic earthquake of moment magnitude Mw9.0
occurred with an epicenter located on the Pacific Ocean off the Oshika Peninsula. This earthquake
induced liquefaction at a significant number of locations in 149 municipalities (cities, special wards,
towns, and villages) within a 500-km long zone that extended from Iwate to Kanagawa Prefectures inthe eastern part of Japan (Fig. 1). The farthest liquefied site from the epicenter of the main shock is
Minami-boso Town, whose epicentral distance is approximately 440 km. Serious damage was caused
to residential houses, pipelines, embankments, agricultural facilities, and port facilities as a result of
the liquefaction. Liquefied sites induced by previous earthquakes are also plotted in Fig 1. It can beseen that liquefaction was induced by the 2011 earthquake in the most of the municipalities whereliquefaction had occurred in the past.
According to the eyewitness testimony of local residents, sand boiling was observed during themain shock at 14:46 March 11; however, in some areas near the Pacific Ocean in northern Chiba andsouthern Ibaraki Prefectures, sand eruption did occur during the largest aftershock, which took place at
15:45 March 11 with an epicenter located on the Pacific Ocean off Ibaraki Prefecture. In some areas,sand boils occurred during minor aftershocks, but the dates and times were not identified precisely
because a number of strong aftershocks occurred at short intervals after the main event.

Iwate

Akita

Miyagi

Yamagata

14:46 Main shock

Fukushima

Tochigi■ Municipalities whereliquefaction occurred during
the 2011 earthquake● Liquefied sites during theprevious earthquakes(Wakamatsu, 2011)

Gunma

Ibaraki
SaitamaTokyo

15:15 Afteshock
Chiba

Base map: ©Tokyo Map Research Co.,Ltd

Minami-Boso Town

Fig. 1 Distribution of cities, special wards, towns, and villages where liquefaction occurred during theGreat East Japan earthquake and liquefied sites in past earthquakes

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SITES OF REPEATED LIQUEFACTION AND THEIR LAND-USE HISTORY,GEOMORPHOLOGY, AND GEOTECHNICAL CONDITIONS
Figure 2 shows distribution of sites where repeated liquefaction was identified during the 2011 Great
East Japan earthquake in Kanto. Most of the sites were located in Chiba and southern Ibaraki
Prefectures--that is, the northern part of the Tokyo Bay area, northern areas of the Kujyukuri plain andthe flood plain in the lower reaches of the Tone River, where liquefaction occurred during the MJ6.7
Chibaken toho-oki earthquake of December 17, 1987. Following the 1987 earthquake, the author
conducted extensive reconnaissance investigation in the affected areas, and consequently liquefied
sites were specified precisely (Kotoda and Wakamatsu, 1989).

IbarakiKasumigaura Lake

Itako

Inashiki
KozakiTone River

Katori

Chiba.
Tokyo

Asahi
Chiba

Sanmu

Urayasu

Sosa

Kujyukuri Plain

Tokyo Bay

Fig. 2 Distribution of sites where repeated liquefaction was identified during the 2011 Great East
Japan Earthquake
Tokyo Bay area
Along the shoreline of Tokyo Bay, land reclamation has been performed since the Edo Era,
especially since the 1950s. Extensive violent sand boils occurred in artificial fill along the Tokyo Bay,particularly in the areas from Urayasu to Chiba, during the 2011 earthquake in places where surface
effects of liquefaction occurred during the 1987 Chibaken toho-oki earthquake. Repeated liquefaction
was identified to occur at a total of 6 sites in Mihama 3-chome, Kairaku 1-chome, and Irifune 4-chome,located in seaside areas of Urayasu City that were filled in between 1965 and 1971. During the 1987
earthquake, a lot of sand boils erupted and water flowed out from the ground in the roads, parks, andresidential lots; minor damage took the form of settlement and cracks to pavement, walls, andgateposts, but no effects of liquefaction occurred in houses and buildings (Photo 1 (a)). In contrast,liquefaction effects were severe during the 2011 earthquake: huge quantities of sand erupted andaccumulated to depths of several dozen centimeters; single-family houses settled and tilted perceptibly
and lifelines were damaged severely (Photo 1 (b)). Figure 3(a) shows the soil profile and SPT N-valuein Mihama 3-chome, where severe sand boils were observed. The soil from the ground surface down
to a depth of 8m is fill composed of loose fine sand and silty sand with silt seams A silt layer of sea
bed sediment lies beneath the fill. The groundwater level is as high as around GL-3 m. The loose fill
up to around 8 m seems to have liquefied in this area.

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Repeated liquefaction at the same site was identified to occur at total of 19 sites in Mihama-ku,
Chiba City (Photo 2 (a) (b)). Many sand boils and ground cracks were observed in schoolyards, parks,
and the yards of housing complexes, but no damage to houses and buildings occurred during the 1987
Chibaken toho-oki earthquake. The effects of liquefaction induced by the 2011 earthquake weresevere: huge amounts of sand erupted, single-family houses settled and tilted substantially, andlifelines were damaged, as was seen in Urayasu. The areas had been filled in between 1966 and 1975
and were mainly composed of loose fine sand fills with SPT N-values less than 10 from the surface toa depth of about 7 m as shown in Fig. 3(b). The loose sandy fills at a depth of 2 to 7m presumed tohave liquefied during the earthquakes.

(a) 1987 earthquake(b) 2011 earthquake (Urayasu City, 2011)
Photo 1 Sand boils due to repeated liquefaction in 3-chome of Urayasu City(a) 1987 earthquake(b) 2011 earthquake (Onizuka et al., 2011)
Photo 2 Sand boils due to repeated liquefaction at Takasu-daisan elementary school, Mihama-ku,
Chiba City
Elv.
Soil Profile
(m)
2
4
6

Fine sand
Sandy clay
Very fine sandSilty fine sand
Sandy silt
Silty fine sand8

Fine sand

10

Sandy silt
Silty fine sand
Sandy clay
Sandy silt

12
14

SPT
N-Value
20 40

Elv.
Soil Profile(m)2
4Fine sand

Sandy silt
Fine sandSilt
8
Fine sand w/ silt
10
Silty fine sand
Sandy silt
12
Fine sand w/ silt
14
6

16

16
18

SPT
N-Value
20 40

Silt

18

Fine sand2020(b) Mihama-ku, Chiba City(a) Mihama, Urayasu City

Fig. 3 Soil profile and SPT N-value in Tokyo Bay area

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Kujyukuri plain of Chiba Prefecture
Kujyukuri plain is located in the south-easternmost part of Chiba Prefecture facing the Pacific
Ocean and is a typical coastal plain consisting of sand bars (including partial sand dunes developed on
the bar) along the shoreline and inland marshes behind and between bars.
Liquefaction occurred in residential areas and farms in the Kujyukuri plain during the 2011
earthquake. Liquefaction effects were most clearly observed in the northern half of the plains closer tothe epicenter: the cities of Asahi, Sosa, Togane, Sanmu, and Kujyukuri Town. Among them,liquefaction-induced damage was the most extensive and serious in Asahi City, where 757 houses
were damaged due to liquefaction (Asahi City, 2011).
Liquefaction had been generated at many sites in the Kujyukuri plain lying in the epicentral
region during the 1987 Chibaken toho-oki earthquake. Single-family houses were damaged byliquefaction, but number of the damaged houses was smaller than in the 2011 earthquake because thisarea was sparsely populated at the time of the 1987 earthquake, and the liquefaction was confined tosmaller local areas.
In the coastal area of the Kujyukuri plain, iron sand mining had been in operation on a large scale
up to the 1970s: excavation was done by open cuts to depths ranging from 5 to 10 m. Iron was
extracted by iron concentrators from excavated sand at the site; the remaining sand was backfilled into
the excavated ground, and finally the land was returned to its owners and used as paddy field (Iioka
Town, 1976; Asahi City, 1988).
Liquefaction is identified to recur at total of 12 sites in this plain: 10 sites in Asahi City and onesite each in Sosa City and Sanmu City, respectively. In Idono-hama, Ashikawa, Nakayari, Shiinauchi,
Nonaka, and Sangawa in Asahi City, houses damaged during the 1987 earthquake were repeatedly
damaged due to liquefaction during the 2011 earthquake. According interviews with city government
officials and local residents, all of the repeated liquefactions occurred in areas formerly excavated andbackfilled for iron mining.
Photo 3 shows damage to a house in Ashikawa, Asahi City, due to repeated liquefaction. The
house in Photo 3 (a) settled about 30 cm and tilted northward (toward the front of the photo), and thebase of the house was separated from the foundation during the 1987 earthquake; two nearby houses
were also affected by liquefaction. Water bubbled up in the surrounding farms and flooded them for awhile. The house in Photo 3 (a) was rebuilt after the 1987 earthquake, but the ground of the lot sank as
a result of the repeated liquefaction during the 2011 earthquake and the newly-built house wasseverely damaged again (in Photo 3(b)). Seven nearby houses, including the two houses damaged
during the 1987 earthquake, were severely affected by liquefaction. According to the owner of thehouse in Photo 3, his lot had been excavated for sand iron mining around 1960, and then backfilled,
and had been used as paddy field. Around 1975, the land was filled up by about 1 m to be used for
housing lot.
At a farmland plot adjoining a factory in Sangawa, Asahi City, sand erupted during both the 1987
and 2011 earthquakes (Photo 4). The factory building settled differentially, and the floor slab showed acrack about 3 cm wide after the 1987 earthquake. The settlement of the factory building increased and(a) 1987 earthquake(b) 2011 earthquake
Photo 3 Damaged to a residential house due to repeated liquefaction in Ashikawa, Asahi City

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Sand boil
Sand boil

Sand boil(a) 1987 earthquake(b) 2011 earthquake
Photo 4 Sand boils and damage to a factory due to repeated liquefaction at Sangawa, Asahi City
Depth(m) Soil Profile

Depth

(m)
2

SPT

Soil Profile N-Value

2

20 40

4

Fine sandFine sand

8

6

10

8
12

Fine sand

6

4

10

Fine sand

SPT
N-Value
20 40

Fine sand

12

Fine sand

14

Fine sand16(a) Excavated and backfilled areas
for iron mining (Liquefied)(b) Natural ground of coastal plain(No effect of liquefaction)
Fig. 4 Soil profile and SPT N-value in Sangawa, Asahi City

the frames of the windows were distorted substantially in the 2011 earthquake. Around the factory, 17
single-family houses were severely damaged due to liquefaction. According to a resident, no houses
were damaged during the 1987 earthquake and small cracks appeared in the pavement.
Figure 4 (a) shows the soil profile and SPT N-value survey conducted in the formerly excavatedand backfilled areas. The upper 4 meters is loose fine sand with SPT N-value less than 10 with highpotential to liquefy, which is presumed to have been backfilled after excavation for iron sand mining.
Ground water level is as high as 0.25 meters. Whereas Fig. 4 (b) shows the soil profile and SPT
N-value in the natural ground at near by site (a), where no effects of liquefaction was observed. Itshows a typical soil profile for coastal plain, that is, upper 9 meters is moderately-dense fine sand withSPT N-value around 20, which is sand bar origin.
Photo 5 shows an aerial plan view of an athletic park in Yoshizaki-hama of Sosa City, with an areaof 27,541 m2 near the Pacific Ocean. In the 1987 earthquake, sand boils with diameters of about 6 m
were observed at nine sites in multipurpose open space with an area of 2879 m2 as shown as Photo 6
and liquefaction-induced lateral spreading occurred in seaside plant observation area. Many fissures
were observed in the slope of the area. The pavement of a walking path located on the ridge of theslide was cracked vertically and settled, and moved slightly downward as shown in Photo 7 (a). No
damage occurred in the administration building of the park, which was supported by a pile foundation.
Similar but more extensive liquefaction effects recurred during the 2011 earthquake: a large quantityof sand erupted; numerous ground cracks and subsidence occurred everywhere in the park; andliquefaction-induced lateral spreading recurred in the seaside plant observation area in the samemanner as during the 1987 earthquake (Photo 5). Photo 7 (b) shows the crack in a walking path with
about a 85 cm slump which occurred at the same point as in Photo 7 (a). The damage mode isremarkably-similar to that in 1987. According to the Yokaichiba City (the former city name before amunicipal merger in 2006) government at the time of the 1987 earthquake, the lot on which the park
was created had been an iron mining field, and then had been used as paddy field before being filled in1981 for construction of the park.

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Photo 6 Photo 5
Seaside plants
observation area

Administrationbuilding

Lateral spreading

Photo 5 View of an athletic park in Yoshizaki-hama,
Sosa City (taken in June, 2011)

Photo 6 Sand boils in multipurpose open
space generated by the 1987
earthquake

Multipurpose
open space(a) 1987 earthquake(b) 2011 earthquake
Photo 7 Damage to a pavement of walking path of the athletic park due to repeated liquefaction in
Yoshizaki-hama (see Photo 5 for location)

Lower reaches of the Tone River
The Tone River is the second longest river and has the largest drainage area in Japan. Along thebanks of the lower reaches of the river, numerous ponds and abandoned river channels were created asa consequence of the shortcut channeling projects which were conducted from the 1900s to the 1930s,
as shown in Fig. 5. These ponds and former river channels were sequentially filled up with the dredged
sand of the Tone River from the 1950s to the 1960s in order to increase rice production (Editorial
Committee of A Hundred Year’s History of the Tone River, 1987). The greater part of the filled area
has been used as paddy fields, but some was turned into residential lots.
Repeated liquefaction at the same site in this area was identified to occur at total of 20 sites inInashiki City and Kwachi Town, Ibaraki Prefecture, and Katori City and Kozaki Town, Chiba
Prefecture. The effects of liquefaction were more severe and widespread during the 2011 earthquake
than during the 1987 earthquake
Violent sand eruptions and numerous large sand craters occurred with diameters of 1 to 3 meters in
the paddy fields during the 1987 earthquake. These effects predominantly developed within the filled
channels and ponds. Figure 6 (a) shows the distribution of sand boils observed in the former rivercourse in Kozaki Town, as identified by field survey and aerial photographs taken after the earthquake.
Numerous large sand boils were formed on the former channel, as shown in Photo 8 (a) and (b); it
seemed that the surficial ground had completely liquefied, but no effects of liquefaction were observedon the small channels flowing along both ends of the former river channel. A few small sand boils
were also formed on the point bar in the convex bank of the former channel where the dredged sandhad not been filled, whereas no surface effect of liquefaction were observed in the concave bank.

681

These observed facts imply that river bed deposits might have liquefied and generated sand boils in
addition to artificial fill.
Figure 6 (b) shows an aerial photograph taken eighteen days after the 2011 earthquake. The greaterpart of the former channel was covered with thick sand boil deposits, and the small channel flowing at
the northern end of the former river channel was completely filled with boiled sand, as shown in Photo
8 (c). According to a local resident, a road north of the channel was flooded by water ejected after theearthquake. A number of large sand boils, with a maximum hole-diameter of 4m, occurred on the point
bar in the convex bank along the former channel, in places where a few small sand boils were formed
during the 1987 earthquake, but no surface effects of liquefaction were observed in the concave bankas was the case during the 1987 earthquake. A residential area located at the lowest end of the former
Yokotone

InashikiGuru-gawa
Photo 9KawachiRokkaku

NIshishiro

Fig.6

Tone River

Katori

Kozaki01km

Fig. 5 Ponds along the Tone River in 1952 (Modified from 1/50,000 topographic map of Sawara)
Residential
area

Tone River

Tone River
ChannelB-4

Photo 8(c)Minor sand boils
B-1
B-2

B-3

Large sand boils
ChannelNo liquefaction effects

Former Channel

Sand crater
Sand boils from fissure(b) 2011 earthquake (satellite image taken on
March 29, 2011 by Google Earth)(a) 1987 earthquake (modified from Kotoda
and Wakamatsu, 1989)

Fig. 6 Distribution of sand boils in former river course in Mukouya, Kozaki Town, Chiba Prefecture
due to repeated liquefaction
Channel(a) 1987 sand boils from fissures(b) 1987 sand boils crate near(c) 2011 sand boils filled up a channel(see Fig. 6(b) for location)near B-2 in Fig 6 (a)B-4 in Fig 6 (a)Photo 8 Sand boils in a former river course due to repeated liquefaction in Mukouya, Kozaki Town

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Elv.
Soil Profile
(m)
2
4
6
8

C lay w/ sandSilt w/ sandFine sand w/ silt
Silt w/ sandFine sandS ilt w/ sandFine sand

SPT
N-Value

Elv.
Soil Profile
(m)

20 40

Clay w/ sand2

Sand w/ clay

4

Silt w/ sand6

Fine sand8

Fine sand

SPT
N-Value

Elv.
Soil Profile
(m)

20 40

2

Fill

4
6
8

Clay
Clay w/ sandSilt w/ sand

SPT
N-Value

Elv.
Soil Profile
(m)

20 40
2
4

Fine sand w/ silt

6

Very fine sand

8

10

10

10

10

12

12

12

12

14

Very fine sand

14

Very fine sand

14

Fine sand w/ silt

SPT
N-Value

Clay w/ sandFine sandSilt w/ sand
Silt

20 40

Fill

Coarse sandFine sand

14

16

16

16

16

18

18

18

18

20

20

20

20

Very fine sand(a) B-1 (Minor sand boils (b) B-2 (Large amount of sand (c) B-3 (No effect of(b) B-2 (Large amount of sandin 1987)
boils from fissures in 1987)
liquefaction in 1987)
boils from craters in 1987

Fig. 7 Soil profile and SPT N-value at Mukouya, Kozaki Town (see Fig. 6(a) for location)
river channel was severely affected by liquefaction: most of the single-family houses, walls,
gateposts,and telephone poles were settled and tilted, and the roads were covered with boiled sand.
Bridge piers river channel was severely affected by liquefaction: most of the single-family houses,
walls, gateposts, of Kozaki Bridge across the Tone River and the river dike were reported to bedamaged due to liquefaction (Katori Civil Engineering Office, 2011). No such effect of liquefaction
had occurred in this residential area during the 1987 earthquake.
The author conducted boring explorations at four sites in the area of Fig. 6 two months after the
1987 earthquake. Figure 7 shows the soil profiles and SPT N-value at B-1 through B-4 in Fig. 6(a).
The borings disclosed that there were five types of loose sand deposits at the Mukouya site: clayey
sand fill composed of hilly sand which covers the ground surface at B-2; fine sand fill composed ofriver bed sand, which lies beneath the hilly sand fill at B-2 and to a depth of two meters from groundsurface at B-4; loose fines sands of point-bar origin which lie to a depth of four meters from thesurface at B-1; fine to coarse sands of river bed deposits with SPT N-value of approximate 10, which
are encountered at three holes except B-3; and very fine sand of deltaic deposits which underlies at allof holes. No distinct differences in water tables at the time of drilling (February, 1988) were foundamong the four boreholes as shown in Fig. 7.
According grain size analysis for sands taken from boreholes and sand boil deposits near theholes, the curves for the sand boil deposits in 1987 are very similar with three types of fine sands ofriver bed deposits, point bar deposits and sand fill of river bed deposits with fine contents, defined as apercentage finer than 0.075 mm in dry weight, less than 10 %. That for sand boils deposits in 2011
earthquake are also below 10 % (Koseki et al., 2012).
Photos 9 (a) to (c) show liquefaction-induced damage in Rokkaku, Inashiki City, during the 1987
earthquake, and Photos 9 (d) to (f) show the damage at the same sites during the 2011 earthquake.
Rokkaku had been a small pond named “Guru-gawa”, with a depth of about 2 meters, that was filled in
1959 with dredged sand from the Tone River by the Construction Ministry. Beginning in the 1970s
residential houses were built after farmland utilization. According to officials of Azuma Village (theformer city name of Inashiki before municipal merger in 2005), more than 20 houses were damaged
due to liquefaction during the 1987 earthquake. The most striking effects occurred at the Photo 9 site:
telephone poles sank, with their height reduced to around 2 m, and the road subsided below the surfaceof the adjacent paddy field (Photo 9 (a)); gateposts tilted slightly (Photo 9 (b)); a small truck parked ina yard was buried by boiled sand (Photo 9 (c)).
Liquefaction-induced damage was also the most serious at the Photo 9 site during the 2011
earthquake: telephone poles sank down and became extremely tilted; roads and farms subsided andwere flooded by ejected water to the extent that the former pond reappeared (Photo 9 (d)); gateposts
settled by as much as 20 cm (Photo 9 (e)); a house built on the lot shown in Photo 9 (c) sank up to 1 m(Photo 9 (f)).

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(a) 1987 earthquake(b) 1987 earthquake(d) 2011 earthquake (Courtesy of Inashiki City) (e) 2011 earthquake(c) 1987 earthquake(f) 2011 earthquake

Photo 9 Damage due to repeated liquefaction in Rokkaku, Inashiki City (for location see Fig. 5)

Reclaimed land around Kasumigaura Lake
Around Kasumigaura Lake, located along the left bank of the Tone River, there had been manylakes and marshy lands up to a century ago; they had been reclaimed by the Ministry of Agriculture
and Forestry during the 1920s and 1930s as part of a project to increase rice production.
Hinode, Itako City, where serious liquefaction-induced damage to houses and lifelines occurred
during the 2011 earthquake, is one of these reclaimed land areas (Fig. 8). The district was reclaimed
from Uchinasakaura Lake in 1947 and had been used as paddy field. It was developed for housing lots
by being raised by an average of as much as 2.8 m with a sand dredging pump from Sotonasakaura
Lake in 1971. Liquefaction effects were observed during the 1987 earthquake within the filled area,and no effects were observed in the reclaimed land without fill. In the filled area, numerous sand boils
occurred, especially around Point A in Fig. 8; water spouted as high as about 5m at Point B in the
figure, and sand boils and depression of the sidewalk was significant at Point C in the figure.
According to Itako City, at the time of the 1987 earthquake, damage to sewage pipes buried to a depthof 3 to 4m was predominant, while no damage was suffered by pipes buried to shallower or deeper
depths of less than 2 to 3m, or more than 4m. Fortunately no serious effects to houses were reported in
the 1987 earthquake.
After the 2011 earthquake, severe and widespread liquefaction effects were observed in the greaterpart of fill-up areas including the area of the 1987 liquefaction, as shown in Fig. 8. Photos 9 (a) and (b)are a comparison of the damage at the same site in the 1987 and 2011 earthquakes. Covers of thegutter along a street were heaved up as a result of liquefaction, a number of telephone poles weredramatically inclined, and a house tilted slightly in the 2011 earthquake (Photo 10 (b)); whereas during
the 1987 earthquake sand boils occurred in the farm adjacent to the street but no effects were observedon the covers of the gutter (in the front part of the photo 9 (a)).
Figure 9 shows a soil profile and SPT N-value in Hinode. The upper 4 meters is fill composed ofloose fine sand, and fluvio-marine silty clay underlies the fill, in turn overlying moderately-dense sand.
The water level is as high as GL-1 m. The loose fine sand fill beneath the water level seems to haveliquefied during the earthquakes.

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Elv.
Soil Profile(m)

Boring (Fig.9)
C
B A

2
4
6

Photo10SPT
N-Value
20 40

Fine sand
Silt

8
10

Sandy silt

12
14
16

Liquefied area in 1987
Liquefied area in 12011

18

Fine sand20

Fig. 8 Areas of liquefaction in Hinode of Itako City
during the 1987 and 2011 earthquakes

Fig. 9 Soil profile and SPT N-value in Hinode,
Itako City (see Fig. 8 for location)(a) 1987 earthquake(b) 2011 earthquake
Photo 10 Damage due to repeated liquefaction in Hinode, Itako City

CONCLUSIONS
Based on a reconnaissance survey of the Great East Japan Earthquake of March 11, 2011,
recurrence of liquefaction at the same sites was identified at a total of 62 sites. As a result, thefollowing conclusions have been reached:
1) Second time liquefaction was observed during the 2011 earthquake at a total of 62 sites in the Kanto
region, where liquefaction occurred during the MJ6.7 Chibaken toho-oki earthquake of December
17, 1987.
2) Comparing the extent and severity of liquefaction effects between the successive earthquakes in1987 and 2011, the effects of the 2011 earthquake are larger than those associated with the 1987 at
every site, but damage patterns are similar at every site.
3) Most of the repeated liquefaction sites are artificially filled or backfilled areas on seashores, lakes,
former river channels, ponds, and excavated areas, but natural sediments such as river bed deposits
seem to liquefy repeatedly.
4) Soil profiles of the repeatedly liquefied sites located in the upper 4 to 5 meters from the groundsurface showed that they were composed of loose fine to medium sand with SPT N-value less than
10. The groundwater levels are as shallow, within 3 meters from the ground surface.

685

ACKNOWLEDGMENTS
The author would like to acknowledge the following people: Prof. Nozomu Yoshida of Tohoku
Gakuin University; Dr. Masashi Matsuoka of the National Institute of Advanced Industrial Science andTechnology; Prof. Junichi Koseki of the University of Tokyo; Mr. Chihiro Yajima of Grass Resourcing
Co., Ltd.; and the students at Kanto Gakuin University who conducted reconnaissance surveys withthe author after the 2011 earthquake. Mr. Tadao Numasaki, Mr. Takashi Itoga, and Mr. Kouich
Sakamoto of the Inashiki City Government and Mr. Tadashi Kuroda of the City Council of Inashiki
City provided information and photographs of liquefaction-induced damage and guidance throughaffected areas. She also thanks late Prof. Kikuo Kotoda, Mr. Takekazu Akagiri, Dr. Kazuo Watanabe
and Mr. Tatsuya Mase who conducted reconnaissance surveys with the author after the 1987 Chibaken
toho-oki earthquake.

REFERENCES
Asahi City (2011). Private communication with the Administration Division of Asahi City.
Asahi City (1988). Private communication with the Administration Division of Asahi City.
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