Additional Informationfor SPAC Method
Nov.23-24, 2008IISEE, BRI, Japan
By T.Yokoi
Pre-Symposium Training Course
7-th General Assembly of Asian Seismological Commission

1Pivoting Array using only 2 seismographs simultaneously(2sSPAC).
Morikawa et al. (2004)
If microtremor is stationary over time, simultaneous measurement at all stations
may be not indispensable but can be replaced with a serious of simultaneous ones atonly two stations.
m2

c1

c2

c3

m3

m1

m6

m5
c4

c5

c6

m4

Attractive especially for deep exploration using long period seismographs, because2
their price is an astronomical number, but time consuming!

Is Array Configuration
Appropriate ?
Perhaps it can be improved a littlemore.

3

Example1
L_ & S_ Tsukb (Modified)
800

57.6m
115.6m200.1m25.0m
43.2m

Phase Velocity

700
600
500

10.8

100.0m173.2m
14.2m
29.0m
50.0m

0.6
0.4
0.2

400
0

300

0200

50

100

150

200

250r

Comparison.dat

100
001

2

34

Fitting to J0(rw/c(w)) is conducted foreach frequency.

5HzTwo /three r
1

SPAC_Coef.
Cal._Bessel

Only One r

Problem of reliability arisesr

Error of the only one datum affect directly
to the estimated value of rw/c(w)Many Data should be used for everyr4frequency to obtain higher reliability

A possible counter measure: variation of radius of triangles.

1 1
r 1: : :
2 4

r 1:

3 3
: :
2 4

Optimum pattern can be a research topic
5

Example2
The same problem is observed in aseverer way.

example2400

Phase Velocity

350
300
250
200
150

15.0m
30.0m
33.5m
42.4m
45.0m
47.4m

100
50
00

12

34

56Hz

Optimum pattern can be a research topic

A possible counter measure1123

1110498 75m

15m 5Constant Interval

672113104956786

Is 3s-L-Shape Array useful ?
Perhaps “Yes”.
It is worth to test it by field observation, because
it will make exploration possible with smaller
budget for equipment
7

Example2
example2
1

If the oblique side is not used…
Phase Velocity

256 14:block_size(=<4096), block_number
11 0.04:nch,dt
0 M 4.0:kflg(=0 no effect),c1(A1),ajudge
10.0 0.1 0.7:st0(sec),overlap_ratio,bw(>3.71/Td)
1.0 8.0:fmin,fmax
10:ndstT0.dat:input file name (A6)
T1.dat:input file name (A6)
T2.dat:input file name (A6)
T3.dat:input file name (A6)
T4.dat:input file name (A6)T5.dat:input file name (A6)T6.dat:input file name (A6)T7.dat:input file name (A6)T8.dat:input file name (A6)
T9.dat:input file name (A6)36 34 45 56 67 78 89 15.0
4 35 46 68 79
30.0
2 36 69
45.0
SPACLT.dat:output file name(a10)
FRNGLT.DAT:output file name(a10)

0.6
0.4
0.2
015.0m
30.0m
45.0m

-0.2
-0.4
0246868Hz

example2400350Phase Velocity

Zcorrel3.prm

0.8

300
250
200
150

15.0m
30.0m
45.0m

100
50
002

4Hz8

Comparison (Calculated Phase Velocity)

Comparison (Observed Phase Velocity)
0.4

0.5

0.35
0.3

Phase Velocity

Phase Velocity

0.4
0.3
0.2
0.1

01

2

3

0.2
0.150.1

withwithout oblique side

00.25

with
without oblique side

0.05

450

6012Hz3Hz

456withoutwith
33495867=

4958679

If microtremor is truly stationary over time (Analogy of 2sSPAC):
Simultaneous measurement using 3
configurations of L-shape Array
with 3 stations

Simultaneous measurement using
L-shape Array with 7 stations
3495

94

86=

3

786566Time

less

moreEquipment

more

less

710

3s-L-Shape Array

3 Vertical Seismometer

3-ch Digital Recorder

3 cables of single channel

H/V
3-ch Digital Recorder

1 Vertical Seismometer &2 Horizontal Seismometers

1 cable of 3channels
113s-L-Shape Array
Vertical Seismometer3 cables of single channel
VerticalSeismometer

Connector Box

3-ch Digital Recorder

1 Vertical Seismometer &2 Horizontal Seismometers
Cable of 3channels

H/V12Estimation of AVS30 from the phase velocity of Rayleigh waves
that has the wave length 40m(Kon’no et al 2007)
SPAC

PS-logging Data

Dispersion Curve

Velocity Structure

At l=40m

Average 0~30m

Vs30mtVs30psComparison

AVS30
O: Sites where PS-logging did not reach to 30m depth.
O: Sites where PS-logging reached deeper than 30m.
The data used are those obtained at 150 strong motion observation stations inYokohama City.

Ratio Vs30mt/Vs30ps: Average 1.0, S.D. 0.25

13

Site Classification (NEHRP 2001)
E:
AVS30<180m/s (Soft Soil), N < 15
D: 180m/s < AVS30 <360m/s (Stiff Soil), 15 < N <50
C: 360m/s < AVS30 <760m/s (Very Dense Soil & Soft Rock), 50<N
Combination of Kon’no et al (2007)’s method with the site classification ofNEHRP(2001) can be used for detailed survey of ground condition and micro
zonation.

Reference:
Kon’no, K, T. Suzuki, Y. Kamata and T. Nagao, 2007, Estimation of Average S-wave Velocity ofGround Using Microtremors at Strong-Motion Sites in Yokohama, Jour. of Japan Society ofCivil Engineering, 63, 639-654 (in Japanese with English abstract).
NEHRP, 2001, Recommended Provisions; National Earthquake Hazard Reduction Program. Part 1.
Provisions (FEMA 368) prepared for the Federal Emergency Management Agency, Washington
DC. Building Seismic Safety Council.
14