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

COMPARISON OF MICRO TREMOR BETWEEN KEKB AND SPring-8
Y. Nakayama, T. Ito, Electric Power Development Co., Ltd., Kanagawa, Japan
R. Sugahara, S. Takeda, M.Yoshioka, H.Yamaoka, KEK, Ibaraki, Japan
S.Matsui, C.Zhang, JASRI, Hyogo, JapanS. Yamashita, ICEPP, University of Tokyo, Tokyo, Japan
Abstract
Stability of ground is preferable for accelerator beam
operation. We have measured micro tremor of ground atthe KEKB and SPring-8 site, where the ground has quite
different characteristics each other.
In this paper, some of analysis results are shown, andthe characteristics of the ground motion at the KEKB site
and those at the Spring-8 site are compared.

Above
Through pass

Firm rock

INTRODUCTION

HardendGroundGraniteBlock

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 hard rockbed 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 theKEKB and SPring-8 site, where the ground has quite
different characteristics each other. KEKB is located on
the diluvium ground in Kanto plain, and SPring-8 on theKamigori meta-gabbro rock area. The KEKB tunnel isburied 10m deep in the ground, and the SPring-8 ring isplaced on the ground surface.
Measurement executed in the accelerator structure isreported. Some analysis results on vertical ground motion
are shown, and those for the KEKB tunnel and those for
the SPring-8 ring are compared. Effect of traffic noise tothe ground motion is also discussed.

The measurement was executed during the machine
shutdown period. The sampling frequency was set to be
100Hz. The condition of measurement is listed in Table 1.

OUTLINE OF THE MEASUREMENT

Table 1: Condition of measurement

Figure 2: Measurement points in the SPring-8 ring
The measurement points were selected to understand theinfluence from utilities and traffic. Four measurement
points were selected along the KEKB ring, one of whichis close to the main street, Higashi-odori, and the others
are far from it. At the SPring-8 ring, four points were also
selected. Accelerator ring structure is placed on the firmrock bed at first point, and it is on the hardened ground byfilling gravels at second point. At third point, there is anthrough path under the ring structure. The sensor wasplaced on a granite block in a building at fourth point.

Condition of Measurement

Facility

NumberMeasurement points in the KEKB tunnel are shown inFigure 1, and those in the SPring-8 ring in Figure 2.

KEKB*4SP-8**

4D12(Power supplybuilding)Higashi-odori

Measurement points

Measuring period
24hours from 13:00 Dec. 27, 2002
24hours from 21:00 June 14, 2003

*10 minutes duration in every hour for 24 hours at KEKB**30 min. consecutive duration for 24 hours at SPring-8

Measurement instruments
D09(Power supplybuilding)

OHO(ExperimentalHall)

D03(Power supplybuilding)Figure 1: Measurement points in the KEKB tunnel

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.

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

RESULTS OF THE MEASUREMENT

Table 3 : Mean RMS for daytime and night time (SPring-8)Comparison by RMS value in time history
The measured data is time history in velocity. We
calculated the RMS of them, and observed the variationaccording to time of the day. We pay attention to thevertical component. Results for the KEKB tunnel are
shown in Figure 3, and those for the SPring-8 ring inFigure 4.
0.0012

10D09 (underground)
D12 (underground)D03 (underground)OHO (underground)wind (Tsukuba: AMeDAS point)

RMS in velocity (kine)

0.00100.000998
70.00080.000760.0006

50.0005

40.0004

30.0003

Wind velocity (m/sec)

0.0011

20.0002

12:00~12:10

10:00~10:10
11:00~11:10

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

06:00~06:10
07:00~07:10

04:00~04:10
05:00~05:10

02:00~02:10
03:00~03:10

00:00~00:10
01:00~01:10

22:00~22:10
23:00~23:10

20:00~20:10
21:00~21:10

18:00~18:10
19:00~19:10

16:00~16:10
17:00~17:10

0
14:00~14:10
15:00~15:10

10.0000
13:00~13:10

0.0001Figure 3: RMS of vertical velocity of ground motionin the KEKB tunnel.
0.00120.0009The mean RMS value in the daytime is 2.25 times larger
than that at night at KEKB. On the other hand, this ratio
between daytime and night time is only 1.28 at SPring-8.
And the mean RMS value in the day time at KEKB is5.77 times larger than that at SPring-8. At night, this ratio
between KEKB and SPring-8 is 3.28. It is thought that thevibration level at SPring-8 is very low because theaccelerator ring is located on the stiff bedrock andisolated from heavy traffic noise. At KEKB, the site isclose to heavy traffic, which causes the difference in themagnitude of ground motion between daytime and nighttime. Although the wind is said to be some source forseismic noise, it is not clear in Figure 3. The main source
looks to be heavy traffic.

The spectra for 24 measurements at KEKB and 48
measurements at SPring-8 for 24 hours were analysed.

4.5
4
3.5

0.00080.000730.0006

2.50.0005

20.0004

1.5Wind velocity (m/sec)

RMS in velocity (kine)

0.0010

Night-time(kine)
6.32 × 10-5
8.65 × 10-5
6.17 × 10-5
5.31 × 10-5
6.61 × 10-5

Spectral analysis

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)
wind velocity (Kamigori: AMeDAS point)0.0011

RockGranite rock
Improved ground
Above under passing
Average of 4 points

Day-time(kine)
9.23 × 10-5
7.90 × 10-5
8.80 × 10-5
7.98 × 10-5
8.48 × 10-50.000310.0002

20:00~21:00

19:00~20:00

18:00~19:00

16:00~17:00
17:00~18:00

15:00~16:00

14:00~15:00

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

11:00~12:00

10:00~11:00

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

07:00~08:00

06:00~07:00

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

03:00~04:00

02:00~03:00

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

23:00~24:00

0
22:00~23:00

0.5

0.0000
21:00~22:000.0001

Figure 4: RMS of vertical velocity of ground motionin the SPring-8 ring.
It can be seen in Figure 3 that the seismic noise is small
at night and large in the daytime. Dividing one day into
two time zones, daytime (9:00-15:00) and night time
(19:00-2:00), mean RMS value for each time zone wascalculated. Results are shown in Table 2 (KEKB) andTable 3 (SPring-8).
Table 2 : Mean RMS for daytime and night time
(KEKB tunnel)
Day-time
Night-time(kine)(kine)
D09 (underground)3.26 × 10-4 1.34 × 10-4D12 (underground)4.04 × 10-4 1.63 × 10-4
D03 (underground)6.23 × 10-4 2.04 × 10-4
OHO (underground)6.02 × 10-4 3.65 × 10-4
Average of 4 points
4.89 × 10-4 2.17 × 10-4

Figure 5: Spectra of vertical ground motionat KEKB tunnel

Figure 6: Spectra of vertical ground motion at SPring-8

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

The duration of measurement is 10 minutes at KEKB and
30 minutes at SPring-8. Those spectra were averaged. The
averaged spectra of vertical ground motion over 24 hours
are shown in Figure 5 for KEKB and Figure 6 for SPring8..
From these results, the level of the ground motion isfound to be extremely lower in the SPring-8 ring than thatin the KEKB tunnel.

COMPARISON OF THE GROUNDMOTION BETWEEN KEKB AND SPring-8
The spectra were classified into two groups, daytime(9:00-15:00) spectra and night time (19:00-2:00) spectra.
And the spectra in each group were averaged.
The spectra for daytime are shown in Figure 7 and thosefor night time in Figure 8. In the figures, two spectra, theone is the highest one and the other the lowest one, foreach KEKB and Spring-8 site are shown. The spectra arevalid in the frequency region less than 25 Hz which is theNyquist frequency corresponding to the sampling rate
100Hz.

artificial noise such as traffic noise and machine noise infactories. At KEKB, the difference in the amplitude
between the daytime and night time is remarkable around
2-3Hz peak, but this difference is not seen around 0.20.3Hz peak. The spectra in the daytime and night time
looks almost the same at SPring-8. Comparing the spectraat KEKB and those at SPring-8, the ground vibration inthe KEKB tunnel is much larger than that in the SPring-8ring. The amplitude at night at KEKB is larger by about
three orders in the power spectra and by about one orderin the integrated spectra than those at SPring-8. In thedaytime, the amplitude at KEKB is larger by about fiveorders in the power spectra and by about two orders in theintegrated spectra than those at SPring-8.

SUMMARY
The micro tremor measurement was executed in theKEKB tunnel and in the SPring-8 accumulation ring. Thefollowings are observed in the analysis of the data.
• The level of the vibration in the KEKB tunnel ismuch higher than that in the SPring-8 accumulation ring.
• The magnitude of the peak around 2-3 Hz in thespectra in the daytime is different from those atnight at KEKB. This difference does not appear atSPring-8.
• The peak around 0.2-0.3 Hz does not vary through24 hours both at KEKB and SPring-8.

ADDRESS OF THANKS

Figure 7: Comparison of the spectra for vertical groundmotion in the daytime between KEKB and SPring-8.

We deeply thank to Professor Kumagai of SPring-8because 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 for
Tev 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., Characteristics of micro tremor in
SPring-8 (Harima), Proceedings of the 14th Symposium ofAccelerator Science and Technology, Tsukuba, Nov. 11-13,
2003.

Figure 8: Comparison of the spectra for vertical groundmotion in the night time between KEKB and SPring-8.
In the spectra, two peaks are observed. One is around0.2-0.3 Hz, which is said to be caused by some natural
phenomena such as ocean swells and wind. The other isaround 2-3 Hz, which is said to be caused by some