Middle East Technical University
Earthquake Engineering Research Center
TÜBİTAK Research Project, No. 105G016
Compilation of Data Base for
The National Strong-Motion Seismograph Network in Turkey
Report on Seismic and Geotechnical Investigations
Seismograph Station
Station Coordinates
Elevation
Location
AI_003_IZN
40.42993 K
29.71925 D
Datum: WGS84
Hükümet Konağı
Station Address
Date of Seismic Survey
Date of Geotechnical Drilling
Structure Type
Number of Floors
3
Hükümet Konağı
Atatürk Cad.
İznik, Bursa
11 May, 2006
30 April - 1 May, 2007
Concrete
Location of Seismograph
Figure 3-1. Location map of station AI_003_IZN.
G Floor
Figure 3-2. A satellite view of the surrounding areas of station AI_003_IZN from 10-km altitude
(from Google Earth).
Figure 3-3. Site sketch for station AI_003_IZN. A: seismograph station, B: center point of the
geophone spread, C: geotechnical borehole location, and Y1 is a building at the site. The blue
line represents the 94-m spread with 48 geophones at 2-m intervals. Shot points 1 and 3 are
located at the two ends, 2-m away from the spread, and shot point 2 is located at the center of the
spread indicated by B. It should be noted that the coordinates of A, B, and C have some error
depending on the GPS satellite positions and the time of measurements.
Figure 3-4. A view of the building, denoted as Y1 in Figure 3-3, where the accelerometer for
station AI_003_IZN is located.
Figure 3-5. A view of the geophone spread at the site of station AI_003_IZN. The locations for
the seismograph station, the geophone spread, and the geotechnical borehole are indicated in the
site sketch shown in Figure 3-3.
Figure 3-6. A view of the geotechnical drilling at the site of station AI_003_IZN. The locations
for the seismograph station, the geophone spread, the geotechnical borehole, and building Y1 are
indicated in the site sketch shown in Figure 3-3.
Figure 3-7. Shot gather 1 recorded at the site of station AI_003_IZN (left) and its amplitude
spectrum (right). This 48-channel record was acquired using a 50-kg accelerated impact source
at the shot location (indicated by the red asterisk) 2-m to the left of a 94-m spread with 48 4.5-Hz
vertical geophones at 2-m intervals. The location of the geophone spread is indicated in the site
sketch shown in Figure 3-3.
Figure 3-8. Shot gather 2 recorded at the site of station AI_003_IZN (left) and its amplitude
spectrum (right). This 48-channel record was acquired using a 50-kg accelerated impact source
at the shot location (indicated by the red asterisk) coincident with the center of a 94-m spread
with 48 4.5-Hz vertical geophones at 2-m intervals. The location of the geophone spread is
indicated in the site sketch shown in Figure 3-3.
Figure 3-9. Shot gather 3 recorded at the site of station AI_003_IZN (left) and its amplitude
spectrum (right). This 48-channel record was acquired using a 50-kg accelerated impact source
at the shot location (indicated by the red asterisk) 2-m to the right of a 94-m spread with 48 4.5Hz vertical geophones at 2-m intervals. The location of the geophone spread is indicated in the
site sketch shown in Figure 3-3.
Figure 3-10. First-arrival times picked from the shot records acquired at the site of station
AI_003_IZN (indicated by the red asterisks at the top) and the corresponding traveltime curves
along the spread (represented by the red curves at the bottom). First, an initial P-wave velocitydepth model is derived from the traveltimes picked from the field records. Then, this initial
model is perturbed iteratively by nonlinear traveltime tomography to estimate a final P-wave
velocity-depth model (Figure 3-11). At each iteration, first-arrival times are modeled and
compared with the actual traveltimes (picked from the field records). Iteration is stopped when
the discrepancy between the modeled (blue curves at the bottom) and the actual (red curves at the
bottom) traveltimes is reduced to an acceptable minimum.
Figure 3-11. P-wave velocity-depth model of the soil column along the geophone spread at the
site of station AI_003_IZN, estimated by nonlinear traveltime tomography applied to the firstarrival times (Figure 3-10) picked from the shot records in Figures 3-7, 8, and 9. By computing
the lateral average of this model, a P-wave velocity-depth profile for the station site was
computed with the numerical values listed in Table 3-1. The numbered asterisks denote the shot
locations. A sketch of the geophone spread and the shot locations is provided in Figure 3-3.
Figure 3-12. One of the end-on shot records at the site of station AI_003_IZN after the isolation
of surface waves. The Rayleigh-type surface waves seen on this record were first isolated from
the refracted and reflected waves by inside and outside mute, then filtered using a 2,4-36,48-Hz
passband to remove low- and high-frequency noise.
Figure 3-13. The dispersion spectrum of the surface waves in the shot record for the site of
station AI_003_IZN shown in Figure 3-12, computed by plane-wave decomposition. In this
figure, the vertical axis represents the phase velocity of Rayleigh waves. Note that each
frequency component of the Rayleigh waves travels at a different speed --- thus the dispersive
character of these waves within the soil column. The largest portion of the Rayleigh-wave
energy often, but not always, is associated with the fundamental mode. For this mode, a
dispersion curve that represents the change of phase velocity with frequency is picked as shown.
Then, this dispersion curve is used in an inversion algorithm to estimate the S-wave velocitydepth profile for the soil column at the station site (Figure 3-14). From the dispersion curve,
maximum depth to which the S-wave velocity can be estimated with sufficient accuracy is equal
to (1/2) * (maximum picked phase velocity / corresponding minimum frequency). As such, for
most of the stations, the S-wave velocity-depth profile that can be considered as the final product
is within the 0-32 m depth interval (Figure 3-14). Also from the dispersion curve, minimum
layer thickness that can be resolved with an accurate S-wave velocity estimate is equal to (1/2) *
(minimum picked phase velocity / corresponding maximum frequency). As such, for most of the
stations, the estimated S-wave velocity-depth profile has a resolution of 1-2 m layer thickness.
Figure 3-14. The S-wave velocity-depth profile (blue curve) and the modeled dispersion curve
(black curve) for the site of station AI_003_IZN. The vertical axis in depth is associated with the
S-wave velocity and the vertical axis in frequency is associated with the dispersion curve as in
Figure 3-13. The S-wave velocity-depth profile was estimated by inversion of the dispersion
curve for the Rayleigh-wave fundamental mode shown in Figure 3-13. In this procedure, an
initial depth-profile for S-wave velocities is iteratively perturbed until a final S-wave velocitydepth profile is estimated. At each iteration, modeled dispersion values and the actual dispersion
values (picked from the dispersion spectrum) as shown in Figure 3-13 (also shown in this figure
as black dots on the black curve) are compared. Iteration is stopped when the discrepancy
between the modeled (black curve) and the actual (black dots) dispersion values is reduced to an
acceptable minimum. The numerical values of the S-wave velocity-depth profile shown here are
listed in Table 3-1.
Figure 3-15. From left to right: P-wave velocity-depth model (same as the model in Figure 3-11 squeezed laterally); the S-wave
velocity-depth profile (same as the profile in Figure 3-14); uncorrected SPT N values measured at 1.5-m intervals; and the simplified
form of the soil profile from the geotechnical borehole. The yellow horizontal lines define the layer boundaries within the soil column
based on the geotechnical borehole log, the blue horizontal line represents the groundwater level (GWL), and the red horizontal line
represents end of the borehole. GWL has not been observed over a long duration.
Table 3-1. P- and S-wave velocities, and uncorrected SPT N values at the site of station
AI_003_IZN. The P-wave velocity values corresponding to the P-wave velocity-depth profile
derived by lateral averaging of the model shown in Figure 3-15 are listed at 1-m depth interval in
the left portion of the table. The S-wave velocity values corresponding to the S-wave velocitydepth profile shown in Figure 3-15 are also listed at 1-m depth interval in the left portion of the
table. The depth intervals and the S-wave velocity values listed in the center portion of the table
also correspond to the S-wave velocity-depth profile shown in Figure 3-15 as derived from
Rayleigh-wave inversion.
Depth
(m)
Vp
(m/s)
Vs
(m/s)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
441
485
554
649
772
922
1089
1250
1383
1474
1517
1530
1546
1565
1585
1607
1633
1662
1692
1724
1756
1788
1819
1848
1875
1895
1910
1922
1933
1941
1949
1955
1960
204
204
204
189
189
189
243
243
243
223
223
223
223
192
192
192
192
192
333
333
333
333
333
333
333
377
377
377
377
377
377
377
377
Depth
Interval
(m)
Vs
(m/s)
0-2.1
2.1-4.8
4.8-8.1
8.1-12.3
12.3-17.5
17.5-23.9
23.9-32
204
189
243
223
192
333
377
Depth
(m)
SPT N
1.5
3
4.5
6
7.5
9
10.5
12
13.5
15
16.5
18
19.5
21
22.5
24
25.5
27
28.5
30
31.5
33
34.5
36
37.5
39
13
7
50
11
12
22
22
26
28
22
7
7
6
5
31
14
24
13
16
16
16
16
12
10
40
50