The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

CHARACTERISTICS OF MICRO TREMOR IN SPring-8 (HARIMA)
Y.Nakayama, T.Ito, Electric Power Development Co., Ltd., Kanagawa, Japan
S.Matsui, C.Zhang, JASRI, Hyogo, Japan
R. Sugahara, S.Takeda, M.Yoshioka, H.Yamaoka, KEK, Ibaraki, Japan
S.Yamashita, ICEPP, University of Tokyo, Tokyo, Japan
Abstract
Stability of ground is preferable for accelerator beam
operation. We have measured micro tremor of ground at
the SPring-8 site.
In this paper, some of analysis results are shown, andthe characteristics of the ground motion at the SPring-8
are discussed.

In the “Ring Measurement”, four measurement points
were selected along the SPring-8 ring. The Spring-8 ring
structure is placed on the firm rock bed at first point, and
it is on the hardened ground by filling gravels at second
point. At third point, there is a through path under the ring
structure. The sensor was placed on a granite block in abuilding at fourth point.

INTRODUCTION
Stability of ground is preferable for accelerator beam
operation. For example, position errors of quadrupole
magnets are required to be less than 5nm in theacceleration area and even 1nm at the collision point in
GLC (Global Linear Collider)[1]. In general, the hardrock bed is stable and has less seismic noise. It is very
important to know the characteristics of the groundmotion to select the site for an accelerator facility such as
GLC. We have measured micro tremor of ground at theSPring-8 site. Spring-8 is located on the Kamigori metagabbro rock area, and the SPring-8 ring is placed on theground surface.
Measurement executed at the SPring-8 site and theSPring-8 ring is reported. Some analysis results onvertical ground motion are shown, and the characteristicsof the ground motion at the SPring-8 are considered.
Effect of traffic noise to the ground motion is alsodiscussed.

OpenFirm rock

GraniteBlock

East gate
High hill

Figure 1: Measurement points in the ”Site
Measurement”
Above
Through path

Firm rock

OUTLINE OF MEASUREMENT
Measurement points
The SPring-8 site is located on the Kamigori metagabbro rock area. The SPring-8 site is located on thevarious foundations due to large-scale site preparation.
We executed two kinds of micro tremor measurement.
One was the "Site Measurement" which we have paidattention to geographical features at the SPring-8 site.
Another was the "Ring Measurement" which we have
paid attention to foundations and structural conditions
under the SPring-8 accumulator ring.
Measurement points in the “Site Measurement” areshown in Figure 1, and those in the “Ring Measurement”
are shown in Figure 2. The measurement points wereselected to understand the influence from utilities andtraffic, and to know the difference of foundations.
In the “Site Measurement”, four measurement points
were selected at SPring-8, one of which is close to thestreet, the other one of which is on the high hill, and theothers are far from them.

Hardened
GroundGraniteBlock

Figure 2: Measurement points in the “RingMeasurement”

Condition of the measurement“Ring Measurement” was executed during the machine
shutdown period. The sampling frequency was set to be
100Hz in all measurement. The condition of measurement
is listed in Table 1.
Table 1: Condition of the measurement
TypePoints

Site M.

4

Ring M.

4

Measuring period
21:00
13,2003
21:00
15,2003Jun

12,2003∼21:00

Jun

Jun

14,2003∼21:00

Jun*30 min. consecutive duration for 24 hours

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

Measurement instruments
In this measurement, we used the servo type velocity
meter VSE355G2 (Resolution: 10e-6 gal, Frequency
band: 0.012-70Hz) and the data logger SAMTAC802H.
These are manufactured by Tokyo Sokushin Co.,Ltd.
Before accumulating data, VSE355G2 and STS-2 werecompared on the same granite block, and the comparison
authorization was executed.

RESULTS OF “SITE MEASUREMENT”
Comparison by RMS value in time history

But it can be seen in Figure 4 that some correlation
between the RMS and traffic existed. It is considered that
there were some influences caused by the traffic on themain street near the east gate and SPring-8 premise road.
Especially we can see the high correlation for the largesized car comparatively.

Spectral analysis
The spectra for 48 measurements at SPring-8 whole site
for 24 hours were analysed. The duration is 30 minutes inthe “Site Measurement”. Those spectra were averaged.
The averaged spectra of vertical ground motion over 24hours are shown in Figure 5.

The measured data is time history in velocity. We
calculated the RMS of them, and observed the variationaccording to time of the day. The RMS is compared withthe wind velocity and traffic. The traffic census wasexecuted at the main road that is close to the east gate. We
pay attention to the vertical component. Results for thecorrelation between the RMS and the wind velocity are
shown in Figure 3, and those between the RMS and thetraffic are shown in Figure 4.
0.00205Open firm rock
Granite block
High hill (long beam line)
East gate
Wind velocity (Kamigori:AMeDAS point)

4.5
4

20:00~21:00

19:00~20:00

18:00~19:00

17:00~18:00

15:00~16:00
16:00~17:00

14:00~15:00

12:00~13:00
13:00~14:00

11:00~12:00

0
09:00~10:00
10:00~11:00

0.5

0.000007:00~08:00
08:00~09:00

1

0.000206:00~07:00

1.5

0.000404:00~05:00
05:00~06:00

0.000603:00~04:00

2

01:00~02:00
02:00~03:00

2.5

0.000800:00~01:00

30.0010

23:00~24:00

3.5

0.0012

22:00~23:00

0.0014

21:00~22:00

RMS in velocity (kine)

0.0016Wind velocity (m/sec)

0.00180.00200.2Open firm rock
Granite block
High hill (long beam line)
East gate
Normalized Traffic (full-sized car)
Normalized Traffic (large-sized car)0.00180.0014

0.18
0.16
0.14

20:00~21:00

18:00~19:00
19:00~20:00

17:00~18:00

16:00~17:00

14:00~15:00
15:00~16:00

0
12:00~13:00
13:00~14:00

0.02

0.0000
10:00~11:00
11:00~12:00

0.04

0.0002

08:00~09:00
09:00~10:00

0.06

0.000407:00~08:00

0.000606:00~07:00

0.08

04:00~05:00
05:00~06:00

0.000802:00~03:00
03:00~04:00

0.1

00:00~01:00
01:00~02:000.120.0010

22:00~23:00
23:00~24:00

0.0012

21:00~22:00

RMS in velocity (kine)

0.0016

Amount of normalized traffic(Total traffic is assumed 1 per day (each size))

Figure 3: Correlation between the RMS of vertical groundmotion and wind in the “Site Measurement”

Figure 4: Correlation between the RMS of vertical groundmotion and traffic in the “Site Measurement”
It can be seen in Figure 3 or 4 that the seismic noise issmall at night and large in the daytime except for thegranite block. Although the wind is said to be somesource for seismic noise, it is not clear in Figure 3. It isthought that the ground motion was not excited because
there was no tall structure and the wind was not so hard.

Figure 5: Spectra of vertical ground motionin the “Site Measurement”
From these results, the spectra for all measurement
points look almost the same on the low frequency sidefrom about 1Hz. However, we can see the difference on
the high frequency side from 1Hz. In the spectra, somepulses around 20Hz are observed at the high hill, and thegentle peaks around 10-20Hz are observed at the east gate.
The pulses are thought to be the influences from theutilities near the long-length beam line. The gentle peak isconsidered to be the influences from the traffic on themain street that is close to the east gate.

Comparison by minute earthquake record
During the “Site Measurement”, the earthquake wasoccurred at about 23:03 June 12, 2003. The hypocenter ofthis earthquake was the Kagoshima Satsuma area (31°59.2" north, 130° 15.9" east, and 155km in depth), andmagnitude was M3.9. We could get the time history data
in velocity as minute earthquake luckily. The examples of
the time history in vertical velocity are shown in Figure 6,
and maximum velocity at the all measurement points islisted in Table 2.
The observed amplitude in velocity at the open firmrock and the granite block was smaller than the others.
Especially, if only this earthquake, it is considered thatthe horizontal component has been amplified more thanthe vertical component. This shows that the characteristicof amplification during the earthquake was obviously
different according to the ground properties and thestructure.

Velocity(kine)

0.00250.002
0.00150.001
0.00050-0.0005-0.001 0-0.0015-0.002-0.0025

Velocity(kine)

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

0.00250.002
0.00150.001
0.00050-0.0005-0.001 0-0.0015-0.002-0.0025

granite block (vertical component)

20

40

60

80

100

120

140

160

However, the peak around 0.2-0.3Hz is almost the samein every measurement points. It is understood that thedegree of seismic noise in the Spring-8 ring is very low.

Time(sec)east gate (vertical component)

20406080

100

120140160Time(sec)Figure 6: Examples of the time history in verticalvelocity during the minute earthquake
Table 2: Maximum velocity during the minuteearthquake
Measurement
PointsOpen firmrock
Granite Block
High Hill
East gate

Maximum velocity (kine)
NSEW
UD-3-3
1.84 × 10
2.19 × 10
1.24 × 10-3-3-3
1.29 × 10
1.35 × 10
1.11 × 10-3-3-3
5.72 × 10
5.74 × 10
2.86 × 10-3-3-3
4.36 × 10
6.02 × 10
2.23 × 10-3

Figure 8: Spectra of vertical ground motionin the “Ring Measurement”

SUMMARYRESULTS OF “RING MEASUREMENT”
Comparison by RMS value in time history
We calculated the RMS of time history in velocity, as
well as the “Site Measurement”. The correlation between
the RMS and the wind is shown in Figure 7. Although thewind is said to be some source for seismic noise, it is notclear. It can be seen in Figure 7 that the variationaccording to time of the day was very small. And it isclear that the RMS of the ground motion was lower thanthose obtained in the “Site measurement”.
5firm rock (west of the ring)
granite block (south west of the ring)hardend ground (south east of the ring)above through pass (north of the ring)velocity of the wind (Kamigori: AMeDAS point)

0.00184.5
420:00~21:00

19:00~20:00

17:00~18:00
18:00~19:00

16:00~17:00

15:00~16:00

13:00~14:00
14:00~15:00

12:00~13:00

0
10:00~11:00
11:00~12:00

0.5

0.0000
09:00~10:00

1

0.0002

08:00~09:00

1.5

0.000406:00~07:00
07:00~08:00

20.0006

05:00~06:00

0.000803:00~04:00
04:00~05:00

2.502:00~03:00

30.001001:00~02:00

0.0012

23:00~24:00
00:00~01:00

3.5

22:00~23:00

0.0014

21:00~22:00

RMS in velocity (kine)

0.0016Wind velocity (m/sec)

0.0020The micro tremor measurement was executed in
SPring-8 site and the SPring-8 ring. The followings areobserved in the analysis of the data•
The level of the ground motion in the SPring-8
ring is lower than that on the ground such as thehigh fill and the east gate.
•From the record of the minute earthquake, it isclear that the amplification characteristic during
the earthquake is different according to the kind ofgrounds.
•The difference is generally small around the low
frequency side, and the variation according to timeof the day of the ground motion is also small at theSpring-8 ring.

Figure 7: Correlation between the RMS of vertical groundmotion and wind in the “Ring Measurement”

Spectral analysis
The averaged spectra of vertical ground motion over 24hours are shown in Figure 8, as well as the “SiteMeasurement”.
The most remarkable point is that only the point above
the through pass has two or more peaks on the highfrequency side around 10Hz. It is thought that these peaks
were excited from some utilities and through pass itself.

ADDRESS OF THANKS
We deeply thank to Professor Kumagai of SPring-8
because this measurement was achieved by hiscooperation. We also thank to the staff of Electric Power
Development Co., Ltd. who helped us in setting
instruments and accumulating data during themeasurement period.

REFERENCES[1] ACFA, JHEPC and KEK, “JLC Project, Linear Collider forTev Physics”, JLC Project Report, March 2003.
[2] Y. Nakayama, et al., Characteristics of micro tremor in
KEKB (Tsukuba), Proceedings of the 14th Symposium ofAccelerator Science and Technology, Tsukuba, Nov. 11-13,
2003.
[3] Y. Nakayama, et al., Comparison of micro tremor between
KEKB and SPring-8, Proceedings of the 14th Symposium ofAccelerator Science and Technology, Tsukuba, Nov. 11-13,
2003.