JOINT CONFERENCE PROCEEDINGS
9th International Conference on Urban Earthquake Engineering/ 4th Asia Conference on Earthquake Engineering
March 6-8, 2012, Tokyo Institute of Technology, Tokyo, Japan

LIQUEFACTION CAUSED BY THE 2011 OFF THE PACIFIC COAST OF TOHOKU
EARTHQUAKE ABD THE RESULT OF THE PRIOR MICROTREMOR MEASUREMENT
Jun Saita1), Yutaka Nakamura2,3), and Tsutomu Sato1)
1) Research Engineer, System and Data Research, Tokyo, Japan
2) President, System and Data Research, Tokyo, Japan3) Visiting Professor, Department of Built Environment, Tokyo Institute of Technology, Japan
jun@sdr.co.jp, yutaka@sdr.co.jp, tsato@sdr.co.jp

Abstract: The 2011 off the Pacific coast of Tohoku Earthquake caused severe damage in a wide sphere. Even in Tokyo
metropolitan area, far from the epicentral area, liquefaction was observed. The basic and proper countermeasure forearthquake disaster is to make all the structure earthquake resistance. For this purpose, it is important to grasp thevulnerability from the inventory survey before the expected event. This paper explains the vulnerability index Kg value
derived from the result of the microtremor measurement and compares the liquefaction caused by this earthquake with theresults of the microtremor measurement conducted in 1990. For example, at Maihama area we had 4 measurement points
as surrounding the Tokyo Disney Land built on a reclamation land in 1990 and calculated Kg value for each point fromthe result of the microtremor measurement. In this area, Kg value was 9.8 to 34.9 (micro strain/Gal) and it corresponds tothe shear strain at the surface ground layer caused by the 2011 earthquake is estimated 700 to 2300 micro strain. From
this result, two points of this measurement are possible to be suffered liquefaction damage. This agrees with the field
investigation by other research group. Other examples around Kanto region will be explained and shows the validity ofthe Kg value.

1. INTRODUCTION
The 2011 off the Pacific coast of Tohoku Earthquake(hereafter the 3.11 earthquake) caused severe damage inwide sphere focusing mainly around eastern Japan area.
Even in Tokyo metropolitan area, more than 200 to 300 km
far from the epicentral area, liquefaction was observed inmany places.
The ultimate and proper countermeasure forearthquake disaster is to make all the structure earthquake
resistance. For this purpose, it is important to grasp thevulnerability from the inventory survey before the expected
event.
This paper explains the vulnerability index Kg value
derived from the result of microtremor measurement andcompares the liquefaction situation caused by the 3.11
earthquake with the results of the microtremor measurement
conducted in 1990.
2. VULNERABILITY INDEX KG VALUE FORGROUND
Vulnerability index K value is an index to estimate thestrain of ground and the focused part of the structure at thetime of estimated earthquake, derived from the predominantfrequency F and its amplification factor A and thedimensions of the structure. The common estimating

equation of the strain g is as follows.

γ or ε = K × a(1)

Here, K and a are K value and the acceleration value
at the base ground, respectively.
In case of ground, Kg value, K value for ground, isdefined as follows;γ = eAd / h= eAa / ω 2 / h= eAa /(2πF ) 2 (4 F / Vs)= eAa /(2πF ) 2 (4 FA / Vb)= eA2 / F /(π 2Vb)
= A2 / Fe /(π 2Vb)a(2)Here, e is input efficiency and Vb and Vs are thevelocity of the base ground and surface layer, respectively.
Hence,

γ e = β × Kg × a(3)Here, Kg = A2/F and β = e/(π2Vb). Vb can be assumed
600m/s in Japan. If input efficiency e is assumed 0.6,
numerical value of β is about 1.0 and then,γ e = Kg × a(4)It seems that the input efficiency can be fluctuated by
the input earthquake motion. In case of the shot duration likepulse wave, large acceleration is required so the input
efficiency will be small. However this earthquake has very
long duration, so input efficiency e can be set 1.0 and then βbecomes 1.7. Thus,γ e = 1.7 × Kg × a(5)The trial on the determination of liquefaction
occurrence using Kg value will be described below.
3. RESULT OF MICROTREMOR MEASUREMENT
AND LIQUEFACTION OCCURRENCE
This paper uses the result of microtremor
measurement conducted in 1990. The instrument for thismeasurement was PIC, Portable Intelligent Collector, amicrotremor measuring tool with a three-component sensor
and data logger units. The microtremor was repeatedly
recorded 40.96 seconds (4,096 data in 100 Hz sampling) at
every measurement site, and a 10.24 seconds length data
was chose from a viewpoint of less artificial noise. Then theselected data was Fourier transformed. After that, thehorizontal to vertical spectrum ratio was calculated for eachcomponent of every measurement and finally H/V spectrum

ratio was derived as the averaged spectrum ratio (Nakamura,***). Predominant frequency F and its amplification factor
A are read from the H/V spectral ratio. These procedures had
been done in 1990.
This paper calculates the Kg value this result andestimates the strain in the surface ground layer with theacceleration value observed nearby site. Then the proposed
index and method are verified their validity with comparing
the estimated strain with the actual liquefaction situation.
3.1 Maihama area
Maihama is a reclaimed area filled in 1970s, locating
at eastern side of Tokyo metropolitan area. Tokyo DisneyLand built on it. In 1990, microtremor measurement wasconducted at four corners of a reclaimed land, MH01 toMH04 as Figure 1. Kg value is calculated from predominantfrequency F and its amplification factor A in 1990. Kg value
ranges 9.8 to 34.9 µ/Gal (=micro-strain/(cm/s/s)) for MH01
to MH04 as shown in Figure 2. A nearby strong motion
station, K-NET Urayasu, recorded 164 Gal (= cm/sec/sec) asmaximum acceleration. Here this maximum acceleration
value is 5HzPGA, 5Hz low passed peak ground acceleration.
And because the amplification factor is assumed about 4times for the ground in this area, maximum acceleration atbase ground can be estimated 41 Gal. In view of aconsiderable long duration time of the 3.11 earthquake, asdescribed before, the input efficiency set 1.0 for thediscussion below.
If input efficiency is 1.0, the strain in the surface
ground is estimated roughly 1050, 1100, 700 and 2300 µ for
MH01 to MH04, respectively. If a strain more than 1000 µcauses liquefaction, it seems that liquefaction occurs at
MH01 and MH02, does not occur at MH03 and severely
occurs at MH04. Figure 1 also shows the result of the fieldsurvey of the liquefaction situation after Yasuda 2011. We
can see that the Kg value distribution agrees with theliquefaction situation.

Red indicates Liquefaction
MH101

舞浜地区のＦ、ＡおよびKg値の分布

Kg Value, Amplification Factor A,
固有振動数Ｆ／増幅倍率Ａ／Kg値
Predominant Frequency F

100
MH04
MH01

Kg値
Kg Value

MH02
MH03

10
増幅倍率Ａ Factor A
Amplification

固有振動数Ｆ Frequency F
Predominant

10.1-10MH102

MH104
MH103

Figure 1 Measurement Point and Liquefaction
at Maihama

1030507090110Distance
TDL駐車場入口付近測点MH01から道路沿いに測った距離：任意スケール

Figure 2 Distribution of Kg Value,
Predominant Frequency Fand Amplification Factor A at Maihama

Figure 3

Distribution of Measurement Point and Reported Damageat Omori and Oi (: Reported Damage)大森・大井埠頭地区と舞浜地区のKg値分布

Nishi-Funabashi

50
OF1345

Kg
Value
計測されたKg値

40MH0435

Minami-Funabashi

30

OF16 OF142520

MH01

MH02

OF107

Shin-Narashino

OF108

15

OF12OF1510

Kaihin-Makuhari

MH03

5Kemigawahama

0050
100
東西測線に沿った距離：任意スケール

150

Inagekaigan

Distance

Figure 4 Distribution of Kg Value at Omori and Oi
3.2 Omori and Oi area
Omori and Oi area locate in south west part of Tokyo
Metropolitan area and main part of Oi had been filled up in
before 1940s. Measurement points were set along EW line
between a park west side of JR Omori station and Oi
container wharf, and along NS line in the center of Oi pier(see Figure 3). Figure 4 shows the Kg value distribution
based on the 1990 measurement. This figure shows that Kg
value exceeds 15 around the wharf and a park in the centerof the reclaimed land. After Tokimatsu 2011, liquefaction
occurs around the pier and also the park in the center ofreclaimed land temporary closed a baseball ground becauseof liquefaction and informed damage as crack at artificial
shore. There is no more information of damage for this area.
Kg values corresponding to this damage information
are small value around 10 except more than 23 at the pierand more then 15 around the park. It shows that liquefaction
must be caused more than 60 Gal of the acceleration at theChibaminato

Soga

Figure 5 Distribution of Measurement Points
for JR Keiyo-Linebase ground if the input efficiency is assumed 1.0. Thus it
seems to be hard to occur liquefaction in case of less than
100 Gal fro the ordinary event with common duration time.
So Kg value distribution gives proper result for thepossibility investigation of liquefaction.
3.3 JR Keiyo-Line
JR Keiyo-Line is running along coastal line of Tokyobay. Microtremor measurement in 1990 was conducted
every 100m for 22.5km between Nishi-Funabashi stationand Soga station (see Figure 5). Figure 6 shows distributionof Kg value for the distance from Nishi-Funabashi station,
the western end of the measured area. An area marked dark

Kg>12 corresponds to about 1000µ10

Kg値
Kg=10=1020
15

海浜幕張
海浜幕張

15

南船橋

西船橋

20

←ここからは震災後のgoogle衛星写真あり
Here and after, it is possible to confirm with Google Map
新習志野

25

南船橋

25

新習志野

30

西船橋

30

105

500
3.0

4.0

6.0

5.0

Kg=10

12.0
13.0

14.0

13.0 16.0
15.0

17.0 14.0
18.0

Kemigawahama

19.0

7.0
1.0

0.0

2.0

3.0 8.0 4.0

5.0

Minami-Funabashi Shin-Narashino

9.0
6.0

10.0 9.0
8.0

7.0

15.0
20.0

Inagekaigan

16.0

17.0

18.0

10.0 11.0
11.0

12.0

Kaihin-Makuhari

蘇我

千葉みなと

稲毛海岸

検見川浜

検見川浜Nishi-Funabashi

2.0

千葉みなと

1.0

稲毛海岸

0.0

19.0

20.0

Chibaminato

21.0

22.0

Soga

23.0

24.0

Figure 6 Distribution of Possible Damage and Kg Value for JR Keiyo-Linepink and light blue indicates a portion of liquefaction and notliquefaction, respectively, after Yasuda (2011). Also lightpink indicates liquefaction after Chiba PrefecturalEnvironmental Research Center (2011). After 7km, purple
part indicates a possible area with liquefaction fromcomparing Google Earth photos before and after theearthquake.

It seems that distribution of Kg value in Figure 6agrees with the result of reconnaissance survey. And at thearea of liquefaction, Kg value is almost more than 10.
Maximum acceleration around this area can be estimatedabout 50 Gal from because observed acceleration wasaround 200 Gal and amplification factor is 4. Withconsidering long duration time, input efficiency can be

Microtremor measurement in 1990

Kashima
Soccer Stadium(20100313, before event)Kashima-Jingu

Kg Value μ/Gal
90
80
70 香60 取駅
50
40
30
20
1000.00

十二橋駅

1.00

KatoriNobukata

2.00

潮来駅

3.00

4.00

5.00

6.00

11.00

12.00

13.00

Junikyo

Itako

延方駅

Itako

7.00

8.00

9.00

10.00

Nobukata(20110312)
鹿島神宮駅

Junikyo

Katori(20110329)

14.00

現鹿島サッカースタジアム駅付近

15.00

16.00

Kashima-Jingu

17.00

18.00

19.00

Kashima
Soccer Studium

Distance from Katori

Figure 7 Distribution of Measurement Points, Possible Damage and Kg Value for JR Kashima-Line

20.00

assumed 1.0, the strain is estimated about 1000 µ when
Kg>12. It is able to be thought that the liquefaction judgment
is almost proper.
3.4 JR Kashima-Line
JR Kashima-Line is running through marsh land innorthern greater Tokyo area. Microtremor measurement in1990 was conducted every 100m between JR Katori station
and JR Kita-Kashima station (current Kashima Soccer
Stadium station). Figure 6 shows distribution of Kg value forthe distance from Katori station, the southern end of themeasured area. An area marked pink and brown indicates apossible area with liquefaction and damage for embankment,
respectively, from comparing Google Earth photos before
and after the earthquake. Although this is not a result ofreconnaissance survey, it seems that the damage relates tothe change of Kg and threshold level is little more than 10 ofKg.
4. CONCLUSIONSThis paper adopted the proposed index forliquefaction occurrence based on the result of microtremor
measurement for the measurement conducted in 1990, andthen compared between the result of determination of theliquefaction possibility and the actual liquefaction situation
at the time of 3.11 Earthquake. As a result, it confirmed thatliquefaction occurred at the site with Kg value more than 15.
This high Kg value corresponds around 1000 µ of a shear
strain for a surface ground caused by an input earthquakemotion, if the input efficiency assumed 1.0 in light of thelong duration time for this 3.11 event. And also the possible
damaged area only from the change of the aerial
photographs before and after the earthquake on Google
Earth agrees with the result of the microtremor measurement
along the railway in 1990.
In this way it recognized that it is possible to evaluate
accurately to possibility of the liquefaction and otherearthquake damage occurrence for supposed earthquake
motion from microtremor measurement beforehand. The
validated technique here is a simple technique to measure
microtremor and it realize an inventory survey. So it will bepossible to take a proper countermeasure based on theordinary investigation technique in detail for an area fell out
by this proposed technique. And also it is possible to confirm
an effect the countermeasure work with a change of
microtremor characteristics before and after the work.
We will be happy if the proposed technique cancontribute a countermeasure for liquefaction.
Acknowledgements:
In this paper, the waveform data was mainly provided by
K-KET of NIED, National Research Institute for Earth Science andDisaster Prevention. The authors would like to sincerely express ourhighest appreciation and gratitude to people and the organizations.

References:Nakamura, Y. and Takizawa, T. (1990), “Ground Motion
Characteristics around the Ooi Reclaimed Land in the Tokyo
Bay Area Estimated by Microtremor Measurements”,
Proceedings of the Eighth Japan Earthquake Engineering
Symposium, 679-684.
Nakamura, Y. (1989), “A Method for Dynamic Characteristics
Estimation of Subsurface Using Microtremor on the GroundSurface”, Quarterly Report of RTRI, Vol.30, No.1, 25-33.
Yasuda Laboratory Web Site on Tokyo Denki Universiyu (2011),
http://yasuda.g.dendai.ac.jp/Tokimatsu, K. et al (2011), Damage for Ground caused by the 2011
off the Pacific coast of Tohoku Earthquake”, Research Reporton
Earthquake Engineering, No. 118, 21-47. (in Japanese)
Chiba Prefectural Environmental Research Center website (2011),
http://www.wit.pref.chiba.jp/ (in Japanese)