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

SOIL SUBSIDENCE MAP OF THE TOKYO BAY AREA
LIQUEFIED IN THE MARCH 11th GREAT EAST
JAPAN EARTHQUAKE
Kazuo KONAGAI1, Toru ASAKURA2, Shota SUYAMA2, Hiroyuki KYOKAWA3
Takashi KIYOTA4, Chikako ETO5 and Kenichi SHIBUYA5
1

Professor, Institute of Industrial Science, University of Tokyo, Japan
konagai@iis.u-tokyo.ac.jp
2
Master’s students, Graduate School of Engineering, University of Tokyo, Japan
3
JSPS researcher, Institute of Industrial Science, University of Tokyo, Japankyokawa@iis.u-tokyo.ac.jp
4
Assoc. Professor, Institute of Industrial Science, University of Tokyo, Japankiyota@iis.u-tokyo.ac.jp
5
Aero-Asahi Co., Japan

ABSTRACT: The March 11th 2011 East-Japan Earthquake has caused sand-liquefaction
over a long stretch of landfills along the coast of Tokyo Bay. An attempt was made to detectsoil subsidence from airborne LiDAR (Light Detection and Ranging) images before and after
the earthquake. To cancel out deep-seated tectonic displacements and systematic errors of
LiDAR, the template matching technique is used for the end-bearing pile-supported buildings
chosen as the template in the source image of the target area of Urayasu. The obtained
subsidence map describes the spatial distribution of soil subsidence in great detail.
Key Words: Great East Japan Earthquake, liquefaction, soil subsidence, LiDAR, digitalsurface model, rehabilitation

INTRODUCTIONTokyo Bay area is a home to millions of people as well as the port/factory zone to support urban lives.
The March 11th 2011 Off the Pacific Coast of Tohoku Earthquake (known as the Great East Japan
Earthquake) has caused sand-liquefaction over a long stretch of landfills along the coast of Tokyo Bay,
leaving many houses tilting and lifelines cut off on and in loosened sediments of sands. After almost
all sands were cleared up for rehabilitation, subsidence of the liquefied area was observed as clear
differences in level between ground floors of pile-supported RC buildings and exposed sidewalks. Theliquefied areas along the coast of Tokyo Bay reportedly reaches 42 km2 (Yasuda, 2011), and there yetremain serious long-lasting concerns about sewage treatment and possible inundations inside levees.
In the July 16 1990 Luzon Earthquake for example, the city center along the meandering river trace of
the Pantal was one of the most seriously liquefied areas where drainage systems were clogged up by
the accumulated sand causing temporary flooding. Some RC buildings along Pelez Boulevard have855

sunken in the liquefied sand with their surrounding soils remained underwater for several months(Yanagisawa et al., 1993a). Alaska area of Aringay (at around 16.385614, 120.3263) has subsided by 1
to 3m such that sea water touched roofs of houses at high tide (Yanagisawa et al., 1993a). In the 1964
Niigata Earthquake, similar problems were reported. About a 640m stretch of Akashi Avenue has
subsided due to liquefaction and remained underwater by about 60cm. The area along Tsusen River
was flooded by tsunami, and remained underwater for about a month (Hokuriku Regional
Development Bureau, 2007). These areas have been frequently inundated in heavy rains since then.
One of the more notorious of these floods was the record rainfall on Aug. 4th 1988, which later led the
Niigata Prefectural Government into the construction of a new drainage pump station at Yamanoshita
lockage (Niigata Regional Development Bureau, 2007). With all those previous examples, it is very
important for relevant organizations to have quantitative information of the soil subsidence to copewith the post-earthquake problems.
Images from an airborne Light Detection and Ranging (LiDAR) system, namely digital surface models(DSMs hereafter), were obtained on April 20th and September 6th 2011 for Urayasu and Funabashi-Mihama
areas, respectively, and an attempt is being made to compare the imageries with those before the earthquake(Konagai K. et al, 2011a). From those analyzed, this paper describes the overall features of soil subsidence
in Urayasu.

DETECTION OF SOIL SUBSIDENCE FROM LIDAR IMAGES
A Light Detection and Ranging (LiDAR) system is capable of rapid and accurate collection of
topographic and elevation data. It consists of three airborne devices, (1) a laser scanner, (2) akinematic airborne Global Positioning System (GPS), (3) an interfaced Inertial Measurement Unit
(IMU), and (4) a fixed, ground-based reference GPS station for detecting the difference between its
position indicated by satellites and a known fixed position for correcting positioning errors. The laser
scanner emits fast pulses from a focused infrared laser which are beamed toward the ground surface
with an oscillating mirror for fast scanning in a sinusoidal pattern. The kinematic GPS measures thespatial position of the platform aircraft, while the IMU records the pitch, roll, and heading of theaircraft.
The obtained high-resolution digital elevation maps (Digital Surface Models) before theearthquake (in December 2006-January, 2007 for the entire target areas) and after the earthquake (onApril 20th 2011 for Urayasu City and September 6th for Ichkawa City, Funabashi City and Mihama
area of Chiba City) are graphic images of pixels having information of their elevations. These images
have different spatial pixel densities as shown in Table 1 for different areas and times, depending on
the safe flight altitudes allowed for the aircraft to fly near the Haneda and Narita International Airports.
The difference in flight altitudes may also yield different errors such as false increase in elevation of
pixels away from nadir of the sinusoidal scanning, etc. In addition to the above-mentioned
system-correlated anomalies, the effect of deep-seated tectonic deformations caused by this earthquake
was really remarkable over the entire stretch of the Pacific coast areas of the eastern Japan (Geospatial
Information Authority of Japan, 2011). However liquefaction-induced shallow soil subsidence can be
simply measured with reference to roof elevations of pile supported buildings such that any potential
horizontal or vertical biases can be eventually canceled out. Therefore, to find the best matching depth
for DSMs to minimize the effect of both the system-correlated anomalies and the tectonic
deformations, template matching technique is used for the end-bearing pile-supported buildings
chosen as the template in the source image of target areas.
Table 1. Spatial resolutions of DSMs at different times and areas
Area
Urayasu
Urayasu
Ichikawa, Funabashi and Mihama
Ichikawa, Funabashi and Mihama

Date of LiDAR survey
December 2006 to January 2007
April 20th 2011
December 2006 to January 2007
September 6th 2011856

Spatial Resolution
0.792 points/m2
4.089 points/m2
0.792 points/m2
1.786 points/m2

Table 2.RC buildings for template matching
Template building
A1
A2
B1
B2
B3
B4
C1
C2
C3
C4
D1
D2
E1
E2
F1
F2
F3

Latitude(degree)35.645125
35.645125
35.647987
35.647906
35.647951
35.653619
35.653457
35.653952
35.653682
35.647951
35.651817
35.651592
35.639417
35.638109
35.644944
35.644673
35.645052

Longitude(degree)139.920240
139.920571
139.913904
139.914026
139.914092
139.901497
139.901585
139.901696
139.901806
139.913949
139.899839
139.900280
139.895500
139.897155
139.891650
139.892025
139.892445

Elevation (m)in 201131.1023
31.1292112.9577
112.9761
112.9663
112.9464
20.9227
20.9132
16.9115
13.581114.3769
14.3778
13.6783
14.2482
13.6680
13.6488
13.4727

Elevation (m)in 2006
31.308331.3419113.1900
113.2367
113.1745
113.1917
21.1300
21.119917.1025
13.7840
14.5829
14.5738
13.8505
14.4560
13.864213.8733
13.6934
AverageStandard deviation

Increment(m)-0.2060-0.2127-0.2323-0.2606-0.2082-0.2271-0.2074-0.2067-0.1910-0.2029-0.2061-0.1959-0.1722-0.2078-0.1962-0.2245-0.2207-0.20780.0193Fig. 1 Template points on a pile-supported RC building

It is to be noted that LiDAR returns (reflections) from water surfaces are known to be of suspectaccuracy, because water has a number of physical properties that vary tremendously and make it apoor reflector of light. Moreover the area has a great tidal range of 1.8 to 2m. Therefore the discussion
hereafter only deals with on-shore soil subsidence.
In Urayasu City, 17 points on flat roofs of total 6 buildings (Table 2) were taken as templates tofind the best matching depth. At each template point, a circle with radius of 3m is drawn around it, andelevations of pixels within this circle are averaged for the representative value of the point’s elevation(Fig. 1). As shown in Table 2, the elevations of the chosen points after the earthquake are 20.78cm

857

lower than those before the earthquake in average with the standard deviation of 1.93cm. This standard
deviation of 1.93cm is considered to be small enough to discuss large soil subsidence that appeared asclear several tens centimeters difference in level between ground floors of pile-supported RC buildings
and sidewalks.
For canceling lateral biases, we need to extract Lagrangian components of displacements. However,Comparing DSMs at different times only allows us to detect displacements in the Eulerian description,in which the description of motion is made in terms of the spatial coordinates which does not follow
the motion of a particular target. One practical method to deal with this problem is to detect edges ofbuildings where elevation changes sharply, and keep tracking the motion of the detected edges.
However, as described previously, the DSMs have a spatial resolution of 4 pixels/m2 at most, which isa little to sparse for sharp edge detection. After the 2004 Mid-Niigata Prefecture Earthquake, Konagai
et al. (2010, 2011b) estimated Lagrangian components of tectonic displacement induced within amountainous terrain of Yamakoshi Village by assuming that tectonic displacement varies gently inspace, and therefore three adjacent nodes of DEM would have the same Lagrangian displacements.
The same method is applied here for detecting lateral Lagrangian displacements of roofs with sloping
surfaces towards walls. As illustrated in Fig.2, several cross-sections of a roof are taken first, and after
those with outshooting objects are excluded, they are averaged for the representative roof shape with
two sloping surfaces towards walls on both sides. If two points on the two sloping surfaces undergo a∆ , their Lagrangian components that represent the rigid
rigid-body-translation movement ∆body movement of the roof can be obtained by solving the following simultaneous equations.
1 ∆
1 ∆

(1)

where,are Eulerian displacements at these two points.
It is noted that even a pile-supported building may not be an appropriate target for lateral templatematching, because piles are laterally flexible enough to be easily deformed by the movements of thesurrounding side soils. Therefore five buildings in areas with no evidence of liquefaction (g, f, k1, k2
and k3 in Fig. 3) are taken among the others as templates.

−Δ z
Δy

before EQ

z

OK!

y

NO!

x

z = a1 y + b1zz = a2 y + b2

after EQ

−δ z2

−δ z1

y

Fig. 2

Template building with sloping roofs for adjusting
40

g
30 N

k1-3

a

f

b

20

k2

k3
k1 e

10

W
-40

E

0
-30

-20

-10

0

10

d20

30

40

-10

c
-20
-30

S

(cm)

-40

Fig. 3 Locations of template buildings in Urayasu (left) and Lagrangian components of lateral shifts
for these buildings (right).

858

Fig. 3 shows the obtained Lagrangian components of lateral displacements. The points on a stableground have shifted about 22.45cm north and 4.92cm west in average with the standard deviations of
9.69cm and 10.35cm, respectively. The DSM after the earthquake was thus moved sideways to cancel
the measured biases. It is noted that the standard deviations for the case of lateral template matching
are larger than that for the vertical case. However these standard deviations of about 10cm are at least
much smaller than the error expected from the edge detection method.

OBTAINED MAP OF SOIL SUBSIDENCE
Fig. 4 shows the obtained soil-subsidence map of Urayasu. The aerial photograph of the same area on
the upper right of the figure was taken in 1948 by the US Army (Geospatial Information Authority ofJapan, 2011b), clearly showing that it was post-World War II when the majority of land reclamation in
Urayasu was undertaken, and the greater part of the city today spreads over the reclaimed land of sanddredged from the Tokyo Bay.

Urayasu in 1948, photo by US Army

Coast in 1948

Coast in 2011

Fig. 5(a)0Fig. 9(a)1kmFig. 4. Soil subsidence map of Urayasu.

859

On this map, subsidence can be seen over the entire stretch of the reclaimed land. In particular,
remarkable subsidence is seen where the aerial photo of 1948 shows darker black indicating thepresence of deeper water at that time. On the other hand, on the long-existing natural land of Urayasu
before the time of land-fills, no or slight subsidence less than 0.1m is seen.
Zooming in on one of residential areas, Benten, a clear blue brush of large soil subsidence is foundrunning across several town blocks as indicated with arrows in Fig. 5. In these residential town blocks,
where strip footings and mat foundations are the most common, houses have sunken in the soil by
about 0.5m in average as shown in Fig. 6(a). The southwestern extension of the brush appeared assand blows lined up in the schoolyard of Miakegawa Primary School (Fig. 7(a)). Later, on April 24,
there appeared a puddle as shown in Fig. 7(b) due to a heavy rain of April 23rd 2011. Fig. 7(b) shows across-section of this school yard where the deepest subsidence of about 0.5m was reached.

Fig. 5(b)(a) Location of stripeA

A’
Fig. 7(b)Fig. 7(a)BB’(b) Southwest extension of the soil subsidence stripe appeared in a school-groundFig. 5 Stripe of soil subsidence of across Benten residential area

860

7
1 7
1 4
9 1
5 6
7 2
9 8
8 9
.
9
8
.
3 9
1 3
, 1
7
,
7 1
4 8
4 9
1 9
4 8
6 0
.
4
5
6
3 .
5
m 3
o o
r
F
T

( )

m
e
c
n
e
d
i
s
b
u
s
l
i
o
S

0.0

-0.5

-1.0
20

30

40

50

60

m

10

e
c
n
a
t
s
i
D

0

70

80

90

70

80

( )

(a) Cross-section A-A’

( )

e
c
n
e
d
i
s
b
u
s
l
i
o
S

2
5
0 9
5 0
9 7
8 5
.
9
9
8
3 .
1 9
3
, 1
7
7 ,
8 1
8 2
3 4
6 8
.
3
5
6
3 .
5
m 3
o o
r
F
T

m

0.0

-0.2

-0.4

-0.6

20

30

40

m

10

e
c
n
a
t
s
i
D

0

50

60

( )

(b) Cross-section B-B’

Fig. 6. Cross sections across stripe of soil subsidence that appeared in Benten residential area. Only
subsidence of house roofs is shown in Fig. 6(a).

(a)Sand blows lined up in school ground
March 19th at 35.638933, 139.895619(b) Puddle appeared in school ground
April 24th at 35.639117, 139.895471

Fig. 7 Extension of the subsidence stripe appeared in a school-ground of Miake Primary School861

Fig. 8. Seawall pushed forward (Photo taken on Aug. 1st, 2011 at 35.63666, 139.931638)

A

A’

Elevation (m)(a) Location of AA’ cross-section on the soil subsidence map
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0

2006
2011

0

10

20

30

40

50

60 (m)(b) Cross-sections of shore-protection work
Fig. 9 Cross-sections of shore-protection work at the southeastern end of Urayasu

862

All these observed features may suggest that the surface soil has spread laterally in the normal
direction with respect to the brush of soil subsidence allowing liquefied sand to force its way easily
through the crack, though no clear evidence was found there. Lateral spread of the ground was moreclearly found near the southeast coast of the city as shown in Fig. 8. Cross-sections AA’ before andafter the earthquake are compared in Fig. 9. This figure shows that the seawall was pushed about 2mforward associated with a half-meter subsidence of its backfill. A flat foot protection work, which
extends over 30m distance from the seawall towards the Tokyo Bay, was also pushed toward the bay
with its pavement overriding the toe of the protection work.

SUMMARY
The March 11th 2011 East-Japan Earthquake has caused sand-liquefaction over a long stretch oflandfills along the coast of Tokyo Bay. The liquefied areas along the coast of Tokyo Bay reportedly
reaches 42 km2, and there yet remain serious long-lasting concerns about sewage treatment andpossible inundations inside levees, etc. An attempt was made to measure liquefied soil subsidence withreference to roof elevations of pile supported buildings. Two sets of Digital Surface Models (DSMs)
were compared with roofs of pile-supported RC buildings as templates for matching, and an exampleof the analyzed images was shown for Urayasu City. It turned out that the elevations of the chosenroofs of RC buildings after the earthquake are 20.78cm lower than those before the earthquake inaverage with the standard deviation of 1.93cm, thus verifying that the method allows for throughdiscussion of liquefaction-induced soil subsidence in a quantitative manner. On the obtained map of
Urayasu, subsidence can be seen over the entire stretch of the reclaimed land. In particular, remarkablesubsidence is seen where the aerial photo of 1948 shows darker black color indicating the presence ofdeep water at that time.
Maps for the other Bay Area are now being prepared, and will appear in later publications.

APPENDIX: GEOGRAPHIC REFERENCE SYSTEM
The soil subsidence map was prepared on the Japanese National Grid System. The Japanese National
Grid System divides Japan into a set of 19 zones assigned with Greek numerals from I to XIX in
principle in a row-by-row pattern starting from the zone at the southwest corner. Exceptions (from
XIV to XIX) are for isolated islands. The surveyed Tokyo Bay area is included in Zone IX with its
northwest corner located at 138.5°E, 36.0°N.

ACKNOWLEDGMENT
The soil-subsidence image prepared here is one of the results of cooperative survey between Konagai
Laboratory, Institute of Industrial Science, University of Tokyo and Aero Asahi Corporation. Aero
Asahi Corporation retains copyright control over Digital Surface Models as their works. The authors
are indebted to the Foundation for the Promotion of Industrial Science who has provided the authors
with financial support for conducting the airborne LiDAR surveys over Ichikawa, Funabashi and
Mihama of the Chiba. The authors’ deepest appreciation also goes to Mr. Horii, Public Sewerage
Division of Urayasu City, Mr. Shigeru Hataya, waterworks department of Chiba Prefecture, Mr.
Toshihiro Yokota, Water Quality Control Department of the National Institute for Land andInfrastructure Management, Ministry of Land, Infrastructure and Transport, who have provided theauthors with valuable pieces of information about the damage to underground sewage systems.

863

REFERENCES
K Geospatial Information Authority of Japan (2004) “Development of methods for practical andprecise use of LiDAR.”
http://www.gsi.go.jp/common/000022304.pdf.
Geospatial Information Authority of Japan (2011a) “Crustal movement caused by the March 11th 2011
Off the Pacific Coast of Tohoku Earthquake detected through continuous GPS monitoring.”
http://www.gsi.go.jp/chibankansi/chikakukansi40005.html.
Geospatial Information Authority of Japan (2011b) “Archives of aerial photographs for tracing thehistory of land.” (Service is temporarily suspended as of Jan. 2012).
http://www.gsi.go.jp/tizu-kutyu.html.
Hokuriku Regional Development Bureau (2007) “Geo-hazard in Niigata.” Hokuriku Regional
Development Bureau, Ministry of Land, Infrastructure and Transport,
http://www.hrr.mlit.go.jp/bosai/hokurikunobosai/jisin/jisinindex.htm.
Konagai, K, Fujita, T., Ikeda, T. andTakatsu, S. (2009) “Tectonic deformation buildup in folded
mountain terrains in the October 23, 2004, Mid-Niigata earthquake.” Soil Dynamics andEarthquake Engineering, 29(2), 261-267.
Konagai k., Shibuya K., Eto C. and Kiyota T. (2011a) “Map of soil subsidence in Urayasu, Chiba,
caused by the March 11th 2011 East-Japan Earthquake.” Bull., Earthquake Resistant Structure
Research Center, IIS, University of Tokyo, 45-48.
Konagai Laboratory (2011b) “Soil subsidence map of Urayasu liquefied in the March 11th East Japan
Earthquake.” Konagai Laboratory, Institute of Industrial Science, University of Tokyo,
http://shake.iis.u-tokyo.ac.jp/home-new/.
Konagai, K. (2011c) “Earthquake-induced soil displacements and their impact on rehabilitations.”
Proc., Japan Academy, 69(5) (Ser.B), 433-449.
Niigata Regional Development Bureau (2007) “Yamanoshita lockage drainage pump station.” Niigata
Prefecture,
http://www.pref.niigata.lg.jp/niigata_seibi/1201107670226.html.
Yanagisawa E, Iai S., Wakamatsu K., Yamazaki J. and Yamazaki F. (1993a) “Damage in Dagupan area.”
Reconnaissance Report on the July 16, 1990 Luzon Earthquake, the Philippines, Japan Society of
Civil Engineers, Series No. 1, 101-124.
Yanagisawa E, Iai S., Wakamatsu K., Yamazaki J. and Yamazaki F. (1993b) “Damage to Structures andliquefaction” Reconnaissance Report on the July 16, 1990 Luzon Earthquake, the Philippines,
Japan Society of Civil Engineers, Series No. 1, 163-178.
Yasuda S. and Harada K., (2011) “Liquefaction-induced damage in the reclaimed lands along Tokyo
Bay.” Japan Geotechnical Society, No. 7, 2011, 38-41.
.

864