accepted paper, 15WCEE

Liquefaction caused by
the 2011 off the Pacific Coast of Tohoku Earthquake andthe Result of the Prior Microtremor Measurement
Jun Saita, Y. Nakamura & T. Sato
System and Data Research Co., Ltd., JapanSUMMARY:
The 2011 off the Pacific coast of Tohoku Earthquake caused severe damage in a wide sphere. Even in Tokyo
metropolitan area liquefaction was observed. The basic and proper countermeasure for earthquake disaster is tomake all the structure earthquake resistance. For this purpose, it is important to grasp the vulnerability from theinventory survey before the expected event. This paper explains the vulnerability index Kg value and compares
the liquefaction caused by this earthquake with the results of the microtremor measurement in 1990. For example,at Maihama area we had 4 measurement points. In this area, Kg value was 9.8 to 34.9 (micro strain/Gal) and it
corresponds to the shear strain at the surface ground layer caused by this earthquake is estimated 700 to 2300
micro strain. So, two points of this measurement are possible to be suffered liquefaction damage. This agrees
with the field investigation.
Keywords: The 2011 off the Pacific coast of Tohoku Earthquake, Microtremor Measurement, K Value, H/V
Spectral Ratio, Liquefaction

1. INTRODUCTION
The 2011 off the Pacific coast of Tohoku Earthquake (hereafter the 3.11 earthquake) caused severe
damage in wide sphere focusing mainly around eastern Japan area. And even in Tokyo metropolitanarea, more than 200 to 300 km far from the epicentral area, liquefaction was observed in many places.
By the way, the ultimate and proper countermeasure for earthquake disaster is to make all the structureearthquake resistance. For this purpose, it is important to grasp the vulnerability from the inventory
survey before the expected event.
This paper explains the vulnerability index Kg value derived from the result of microtremor
measurement and adopts Kg value for the microtremor measurement in 1990 to estimate thepossibility of liquefaction. Then Kg value compares the liquefaction situation caused by the 3.11
earthquake.

2. VULNERABILITY INDEX KG VALUE FOR GROUND
Vulnerability index K value is proposed as an index to estimate the strain of ground or the focused partof the structure against estimated earthquake motion, derived from the predominant frequency F andits amplification factor A of microtremor, and the dimensions of the structure. The common estimating
equation of the strain γ or ε is as follows.

γ or ε = K × aHere, 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, is defined as follows;(2.1)

accepted paper, 15WCEE

γ = eAd / h= eAa / ω 2 / h= eAa /(2πF ) 2 (4 F / Vs )= eAa /(2πF ) 2 (4 FA / Vb)(2.2)= eA2 / F /(π 2Vb)
= A2 / Fe /(π 2Vb)a
Here, e is input efficiency and Vb and Vs are the velocity of the base ground and surface layer,
respectively. Also d is displacement at ground surface and h is depth of the surface ground. Hence,

γ e = β × Kg × a(2.3)

Here, Kg = A2/F and β= e/(π2Vb). Vb can be assumed 600m/s in Japan. If input efficiency e isassumed 0.6, numerical value of β is about 1.0 and then,γ e = Kg × a(2.4)

It seems that the input efficiency e can be fluctuated by the input earthquake motion. In case of theshot duration like pulse wave, large acceleration is required to cause large strain so the input efficiency
e will be small. However this earthquake has very long duration, so input efficiency e can be set 1.0
and then β becomes 1.7. Thus,γ e = 1.7 × Kg × a(2.5)

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, a microtremor measuring tool with athree-component sensor and data logger units. The microtremor was repeatedly recorded for 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 the selected data was Fourier transformed.
After that, the horizontal to vertical spectrum ratio was calculated for each component of every
measurement and finally H/V spectrum ratio was derived as an averaged spectrum ratio (Nakamura,1989). 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 from this result in 1990 and estimates the strain in the surface
ground layer with the acceleration value at the time 0f 2011 event observed nearby sites. Then theproposed index and method are verified their validity with comparing the estimated strain with theactual liquefaction situation.
3.1. Maihama area

Maihama is a reclaimed area filled in 1970s and locates at eastern side of Tokyo metropolitan area.
Tokyo Disney Land built on it. In 1990, microtremor measurement was conducted at four corners of areclaimed land, MH01 to MH04 as Figure 3.1. Kg value is calculated from predominant frequency Fand its amplification factor A in 1990. Kg value ranges 9.8 to 34.9 µ/Gal (=micro strain/(cm/s/s)) forMH01 to MH04 as shown in Figure 3.2. A nearby strong motion station, K-NET Urayasu, recorded
164 Gal (= cm/sec/sec) as maximum acceleration. Here this maximum acceleration value is 5HzPGA,

accepted paper, 15WCEE

5Hz low passed peak ground acceleration to restrict the acceleration value to explaining the damage
situation properly. And because the amplification factor is assumed about 4 times for the ground in
this area, maximum acceleration at base ground can be assumed 41 Gal. In view of a considerable long
duration time of the 3.11 earthquake, as described before, the input efficiency e set 1.0 for thediscussion below.
If input efficiency e is 1.0, the strain in the surface ground is estimated roughly 1050, 1100, 700 and2300 µ for MH01 to MH04, respectively. If a strain more than 1000 µ causes liquefaction as it is often
expressed, it seems that liquefaction occurs at MH01 and MH02, does not occur at MH03 and severely
occurs at MH04. Figure 3.1 also shows the result of the field survey of the liquefaction situation afterYasuda, 2011. We can see that the Kg value distribution agrees with the liquefaction situation.
After Prof. Yasuda of TDU.

This air-photo was shoot at 1990.
MH101

MH102

MH104
MH103

Figure 3.1. Measurement Point and Liquefaction Situation at Maihama Area

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

Distribution 舞浜地区のＦ、ＡおよびKg値の分布
of F, A and Kg value at Maihama
100
MH04
MH01

Kg Value
Kg値

MH02
MH03

34.9

10Aplification
増幅倍率ＡFactor A
PrediminantFrequency F
固有振動数Ｆ10.1-101030507090110
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
Distance in units of 30m

Figure 3.2. Distribution of Kg value, Predominant Frequency F and Amplification Factor A at Maihama Area

accepted paper, 15WCEE
3.2. Omori and Oi area

Omori and Oi area locate in south west part of Tokyo Metropolitan area and the main part of Oi had
been filled up in before 1940s. Measurement points were set along EW line between a park west sideof JR Omori station and Oi container wharf, and along NS line in the center of Oi pier (see Figure 3.3).
Figure 3.4 shows the Kg value distribution based on the 1990 measurement. This figure shows that Kgvalue exceeds 15 around the wharf and a park in the west side of the reclaimed land. After Tokimatsu
2011, liquefaction occurs around the pier, and also a park in the center of reclaimed land temporaryclosed a baseball ground because of 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 atthe pier and more then 15 around the park. It shows that liquefaction must be caused more than 60 Galof the acceleration at the base ground if the input efficiency is assumed 1.0. Thus it seems to be hard tooccur liquefaction in case of less than 100 Gal from the ordinary event with common duration time. SoKg value distribution gives proper result for the possibility investigation of liquefaction.

★
★

Figure 3.3. Distribution of Measurement Point and Reported Damage at Omori and Oi Area
( : Reported Damage)大森 大井埠頭地区と舞浜地区のKg値分布
50
OF1345Kg
Value
計測されたKg値

40MH043530

OF16 OF142520MH01MH02OF107

OF108

15OF12OF1510MH03

50050100東西測線に沿った距離：任意スケール

150Distance

Figure 3.4. Distribution of Kg Value at Omori and Oi Area

3.3. JR Keiyo-line

JR Keiyo-Line is running along coastal line of Tokyo bay. Microtremor measurement in 1990 wasconducted every 100m for 22.5km between Nishi-Funabashi station and Soga station (see Figure 3.5).

accepted paper, 15WCEE

Figure 6 shows distribution of Kg value for the distance from Nishi-Funabashi station, the western endof the measured area. An area marked dark pink and light blue indicates a portion of liquefaction andnot liquefaction, respectively, after Yasuda, 2011. Also light pink indicates liquefaction after Chiba
Prefectural Environmental Research Center, 2011. After 7km, purple part indicates a possible areawith liquefaction from comparing Google Earth photos before and after the earthquake.
It seems that distribution of Kg value in Figure 3.6 agrees with the result of reconnaissance survey.
And at the area of liquefaction occurence, Kg value is mostly more than 10. Maximum acceleration
around this area can be estimated about 50 Gal because observed acceleration was around 200 Gal andamplification factor is assumed 4. With considering long duration time, input efficiency can beassumed 1.0, and the strain is estimated about 1000 µ when Kg>12. It is able to be thought that theliquefaction judgment is almost proper.
Nishi-Funabashi

Minami-Funabashi
Shin-Narashino
Kaihin-Makuhari
Kemigawahama
Inagekaigan
Chibaminato

Soga

Figure 3.5. Distribution of Measurement Points for JR Keiyo-line
Kg>12 corresponds to about 1000µ301010

海浜幕張
海浜幕張
海浜幕張
海浜幕張

1055

5
2.0
2.0

3.0
3.0

4.000.0

6.0

7.0
1.0
7.0 2.0
2.0

10.0
3.0
6.011.0
13
8.04.0
9.0
10.0 9.0
11.0
1
3.08.04.0 5.0
5.0 9.0
6.0 7.0
7.0 8.0
8.0
9.0 10.0
10.011.0
11.0 12.0
12.0 12千葉みなと

千葉みな とMinami-Funabashi Shin-Narashino

千葉みなと
稲毛海岸
稲毛海岸

千 葉みな と

検見川浜
検見川浜

稲毛海岸
稲毛海岸

Nishi-Funabashi

5.0

Kaihin-Makuhari

蘇我

1.0
1.0

蘇我

00
0.00.0

検見川浜
検見川浜

新習志野
新習志野

15

新習志野

20

西船橋

151525

Kg値
Kg=10=10

南船橋

2020

西船橋
西船橋

2525

←こここ
こかからはらは震震災
災
後後ののgoogle衛
google衛星星写
写真
真あありりconfirm with Google Map
Hereandafter,
it is possible
to南船橋

3030

Kg=1013.0
15.0
13.0
18.0
12.0
13.016.0
14.0
15.0
0 12.013.0 14.0
14.0 15.0
15.0
16.0 17.0
17.014.0
18.0 19.0
19.0 20.0
20.0

16.0
16.0

17.0
17.0

Kemigawahama Inagekaigan

Liquefaction：

18.0
18.0

19.019.0

Chibaminato

20.020.0

21.021.0

22.022.0

Soga

23.023.0

24.0 24.0

By Yasuda(2011) Chiba Envi. Research Center Google Earth

No Liquefaction： By Yasuda(2011)
Figure 3.6. Distribution of Possible Damage and Kg Value for JR Keiyo-lineaccepted paper, 15WCEE
3.4. JR Kashima-line

JR Kashima-Line is running through marsh land in northern greater Tokyo area. Microtremor
measurement in 1990 was conducted every 100m from south to north between JR Katori station andJR Kita-Kashima station (current Kashima Soccer Stadium station). In this area, we have noinformation of liquefaction occurrence totally along the railway line. So we have compared aerial
photos opened by Google Earth to find out differences between before and after the earthquake. Figure
3.7 shows distribution of Kg value for the distance from Katori station, the southern end of themeasured area. An area marked pink and brown indicates a possible area with liquefaction and damage
for embankment, respectively, from comparing Google Earth photos. Although this is not a result ofreconnaissance survey, it seems that the damage relates to the change of Kg value and threshold levelfor damage occurrence is little more than 10 of Kg.

Figure 3.7. Distribution of Measurement Point, Possible Damage and Kg Value for JR Kashima-line

4. CONCLUSIONSThis paper adopted the proposed index for liquefaction occurrence based on the result of microtremor
measurement for the measurement conducted in 1990, and then compared between the result ofdetermination of the liquefaction possibility and the actual liquefaction situation at the time of 3.11
Earthquake. As a result, it confirmed that liquefaction occurred at the site with Kg value more than 12.
This high Kg value corresponds around 1000 µ of a shear strain for a surface ground caused by an
input earthquake motion, if the input efficiency assumed 1.0 in light of the long duration time for this3.11 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 the possibility of the liquefaction andother earthquake damage occurrence for supposed earthquake motion from microtremor measurement
beforehand. The validated technique here is a simple technique to measure microtremor and it canrealize an inventory survey. So it will be possible to take a proper countermeasure based on theordinary investigation technique in detail for an area fell out by this proposed technique. And also it ispossible 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 can contribute a countermeasure for liquefaction.

accepted paper, 15WCEEAKCNOWLEDGEMENT
In this paper, the waveform data was mainly provided by K-KET of NIED, National Research Institute for Earth
Science and Disaster Prevention. The authors would like to sincerely express our highest appreciation andgratitude to people and the organizations.

REFERENCES
Nakamura, Y. and Takizawa, T. (1990). Ground Motion Characteristics around the Ooi Reclaimed Land in theTokyo 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 Ground Surface, 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)