Waterfront Seismic Survey Report

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Report on Refraction Seismic Survey

Waterfront Condominium & Service Apartment BuildingPattaya

Prepared for

Ten consultant Co., LTD.

ByDepartment of Geotechnology

Faculty of Technology Khon Kaen University Amphoe Muang Khon Kaen 40002 Thailand

29 February 2012



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Refraction Seismic Survey Report

Waterfront Condominium & Service Apartment Building project, Pattaya

Introduction:

Surface geophysical investigation is the mean of indirect measurement of subsurface

geological conditions such as depth to bedrock or overburden thickness, degree of weathering

and geological discontinuities. Refraction seismic survey was undertaken towards determining

the overburden thickness and delineating the bedrock interface as well as assessing rock

quality.

The approximately site location is shown in figure 1. Seismic survey lines are shown in

figure 2.

Figure 1 Location map of Project site (from Google earth)



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Figure 2a Proposed Seismic survey line location

Figure 2b Actual Seismic survey line location



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Field Operation:

Personnel engaged:

Mr. Winit Youngme Engineering geologist, Geotechnology dept. KKU

Dr. Rungroj Arjwech Geologist, Geotechnology dept. KKU

Mr. Sakorn Saengchomphue Technician, Geotechnology dept. KKU

Mr. Suttipat Rattanapongpien Geotechnology student, Geotechnology dept. KKU

Mr. Surat Sukthontan Geotechnology student, Geotechnology dept. KKU

Mr. Phichet Chaithongsi Geotechnology student, Geotechnology dept. KKU

Seismic Instrument Specification:

The seismic equipment used in this prospecting is a system of portable digital signal

enhancement engineering seismograph (24-channel). The system consists of the following:

Seismograph : Model GEODE-24, Geometrics inc., USA

Geophone : Single, 100 Hz, OYO Geospace Inc. USA

Source : 5.5 kg hammer, strike on steel plate, explosive, 0.5 m buried

Cable : 2-12 take-outs with 15 m spacing and 15 m lead-in, OYO

corporation, Japan,

Trigger switch : mechanical contact type for hammer and Geometrics blaster

for explosive.

The field acquisition in one setup called survey spread or line is set of 24 geophone

stations with 5 m geophone spacing.

Geomorphology and Geology

The area is situated in front of Pattaya Bali Hai pier, Pattaya municipal area, west of

Sukhumwit road, about 3,500 m. from Sukhumwit road. The topography is sloping to the northwith lowest elevation of 15 m and highest of about 35 m above sea level. The topsoil is

generally sandy-clayey gravelly soil with subsurface of decomposed granite and quartzite. The

elevation of the area is about 15 - 35 m. above mean sea level.

The rock unit in this area is Carboniferous/Triassic granite overlain by meta-

sedimentary rock sequence of sandstone mudstone shale and gravelly soil of Quaternary

period. The degree of weathering is decomposed to slightly weathered in shallow depth and

fresh rock at the depth of about 40 m.



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Theory and Method:

Seismic exploration, in principle, is nothing more than a mechanized version of the

blind person and his cane. In place of the tapping cane, we have a hammer blow on the

ground, or an explosion in a shallow hole, to generate compressional, or sound, waves.

(Seismic methods also work with shear waves as well.) We "listen" with geophones, spring-

mounted electric coils moving within a magnetic field, which generate electric currents in

response to ground motion. Careful analysis of the motion can tell us whether it is a direct

surface-borne wave, one reflected from some subsurface geologic interface, or a wave

refracted along the top of an interface. Each of these waves tells us something about the

subsurface. In this project, refracted seismic wave is use then we called refraction seismic

survey.

Physically, the seismic refraction method is based on the fact that differences occur

between the velocity of elastic (sound) waves in different geologic formations. The velocity of

seismic P wave in air is about 340 m/sec, in soil layer, between 250 - 1,800 m/sec and in fresh

or sound igneous rocks some 4,000 - 6,000 m/sec. The refraction method makes use of the

fact that when an elastic wave strikes a discontinuity or interface in the ground, the wave is

refracted. If the underlying layer is more compact and has a higher velocity, the wave is

refracted towards the horizontal, if the layer has a lower velocity, the wave is refracted towards

the vertical. If the wave strikes the interface at the critical angle, it is refracted along the

interface. The amount that the wave is refracted is determined by Snell’s law, which states that

(sin i / sin r) = (V1/V2)

Where i is angle of incidence, r is angle of refraction

V1 is velocity of wave in incidence medium

V2 is velocity of wave in emergent medium



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Figure 3 Wave path and correspond T-X plot

When r is 90 degree, sin i1,2 = V1/V2. The refraction along and parallel to the interface

is of vital importance in the seismic refraction method. It occurs when ever the incident wave

strikes the interface at the critical angle. In figure 3 illustrates a simple two layer case with

horizontal layering and constant velocities V1 and V2. It is assumed that V2 is greater than V1.

The cross-section (lower part of figure 4) shows the wave fronts ray paths in the layer. In the

upper layer, the waves propagate from the impact point as hemispheres at a velocity of V1.When the elastic waves reach the second layer, they travel at the higher velocity of V2. It is

evident that (for example) 0.04 second after the impact distant, the positions of the wave fronts

on the ground and in the bedrock are considerably displaced horizontally. Due to oscillations at

the interface between the two layers when the wave travel in the lower medium, ground

vibrations are created in the upper layer. These vibrations return to the surface in the form of

plane wave fronts which make and angle of i1,2 with the interface (sin(i 1,2) = V1/V2). That is to

say, they are critically refracted.



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In the immediate vicinity of the impact point, the waves in the upper layer are the first

to reach the geophones implanted on the ground surface. At a distance that is generally 3-5

times the depth to bedrock (interface, so far), the waves traveling the longer but faster route via

the V2 - layer will overtake the others. The turning point is the outcropping on the ground

surface of the wave front contact.

A corresponding T-X plot is presented in the upper part of figure 3. The conventional

way to interpret and analyze the measured data is to plot the arrival times for each channel on

a T-X graph in relation to distances between the geophones. Lines connecting the plotted

arrival times indicate the velocities (inverse slopes) in the various subsurface layers. The

intersection between these lines corresponds to the outcropping of the wave front contact.

The distance between the impact point and the intersection (breaking point) of the

velocity lines can be used to calculate the depth at the impact point. This is called the critical

distance method. The depth is obtained using the following equation:

h1 = (Xc/2)*[(V2-V1)/(V2+V1)]1/2

where h1 = depth

Xc = critical distance (impact point to intersection of velocity lines)

V1, V2 = layer velocities computed from T-X plot.

Another method of calculating the depth at the impact point is to prolong the velocity

line of the V2 - layer back to the vertical line through the impact point. The time from the impact

instant to the intersection between the vertical line and the velocity line is then used to calculate

the depth. This called the intercept time method. Thus,

h1 = (TiV1)/2(cos i1,2) , where Ti = intercept time

The equations given above are only valid for two layers with horizontal bedding. For

multi-layer case or when the layers are dipping, the equations are considerably more

complicated. At present, there are numerous interpretation methods, ranging from the very

simple like the two which illustrated above, to the complex. The interpretations based on the

ray theory are developed into analytical and graphical methods. Computer programs have been

developed for interpretation of refraction data based on the generalized reciprocal method

(PALMER, 1980), ray tracing (SCOTT, 1973, ACKERMANN et. al., 1980), wave equation

modeling or finite difference method (KELLEY, et. al., 1976). Use of analytical technique issought for fast and accurate handling of refraction data as compared to the graphical technique



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which is very much time consuming. Our office, Geotechnology department in the faculty of

Technology Khon Kaen University uses a computer program to process seismic refraction

survey data with commercial name “SeisImger 2D” based on all above theories.

Data Acquisi tion, Processing and Presentation:

Acquisition:

Refraction seismic exploration using hammer striking on steel plate for end- and

middle-shot, and there is no far shots in this exploration because of site limitation. The

geophone spacing is 4 m, so in one geophone spread of 24 geophones is 92 m long. Once 24

geophones are firmly planted along the planned survey line, geophone cables are connected to

all geophones and to the GEODE. Hammer or trigger switch with extension cable is connected

to GEODE. Since GEODE needs to control from notebook computer, a notebook and power

supply are connected to GEODE. After appropriate setup for data acquisition is completed,

then hammer is strike the steel plate to generate seismic wave. If seismic wave amplitude

obtained is not high enough to read the time break, additional strikes are needed to enhance

seismic wave amplitude. Repeat this step until wave amplitude satisfy the wave size for reading

travel time (normally 5-8 times). Records wave data, shot location, geophone spacing and

other information for further processing.

Five shot points in one survey line (at sta. 0.0, first geophone (G1), intermediate shot(between G6 & G7, G12 & G13 and G18 & G19), and at last geophone (G24), is the survey

design, and called S1, S2, S3, S4, and S5, respectively. Shot point at sta. 0.0 (G1) and sta. 92

(G24) is called end-shot whereas the rests are called intermediate shot. The typical

corresponding T-X plot is shown in figure 4 below. Theoretically, far shots are for deep layer

wave velocity determination whereas intermediate shots are for overburden velocity

determination.



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Figure 4 Example of T-X plot

Processing and Presentation:

The seismic refraction field acquired data is needed to process to get the velocity

information of geological condition under survey line. The step of data processing and

presentation is as in the following:

1. First arrival time reading and time-distance plot

The travel time and survey information recorded from the field for each spread is then

readout for use as seismic data to draw travel time – distant or T-X plot. The velocity of each

layer is then computed using this time - distant plot. The thickness of each layer is also

calculated for each geophone using intercept time, critical distant and delay time techniques.

For good recorded field data, travel time is picked using first-pick function in SeisImager 2D.

For poor recorded field data, the noise filtering and amplitude re-sampling is applied for better

data and manual picking to get travel time.

2. Seismic wave velocity layer profi les

After a T-X or time - distant plot is drawn, the validity of reciprocity of the spread is also

check. The number of layer, layer velocity and thickness are determined. Since SeisImager 2D

is semi-automate package, elevation of each geophone, initial velocities from TX of each layers

are assigned to model to generate initial seismic profile. The package is then calculated the

theoretical T-X and matching to field T-X whereas initial profile is also adjusted. The result of

this step is presented in percentage of root mean square error or rms between field and

theoretical values. For good result, rms error should keep as low as possible. In this



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exploration, all survey lines are come up with rms error less than 5.0 percent. Figure 5 shows

T-X plot with velocity line and adjusted seismic profile after several iterations.

Figure 5 T-X plot with velocity line (above) and obtained seismic profile (below)

The complete of survey results including reading first arrival time, T-X plot, layer

velocities, and interpreted profile are shown in the results part and in the appendix. In this

section only interpreted profiles of survey line are presented.



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Results and Interpretation:

Three (3) seismic survey lines were measured with total length of 218.5 m. The

locations of each line are shown in figure 2 which spread over the project area. Two lines

(geophone spread) located as longitudinal line (line 1 and line 2). One line located across

longitudinal lines. The overall seismic P-wave velocity are ranging from a few hundred (370)

meters per second in loose soil layers to almost 4,000 m/sec in fresh or hard bedrocks. In

summary, table 1 shows seismic line length, the result of each line can be described as follows:

Table 1 Summary of Seismic line length

Line no. Location No of Geophone Length, m

Line 1 Longitudinal pile location 24 92

Line 2 Longitudinal pile location 24 92

Line 3 Cross pile location 24 34.5

Total length 218.5

Line 1 (Longitudinal pile location), this line is located close to hillside, start from

west to east. Total line length is 92 m, and lie generally east-west direction. There are 3

velocities can be observed in this line, with V1 of top soil or backfill/overburden of 371-763

m/sec, V2 (second layer) would be slightly weathered or fractured bedrocks with velocity of

1,154-2,417 m/sec, and V3 of about 4,000 m/sec which would be fresh or hard basement rock.

Table 2 shows seismic velocity of this line. The thicknesses of these strata are varies and

shown as cross section (or profile) in figure 6.

Table 2 Velocity of line 1

Layer Velocity, m/sec Expected geological material

1 450 (371-763) Loose top soil, sandy to compact gravel

2 1,500 (1,154-2417) Slightly weathered or fractured rocks

3 4,000 Fresh or hard bedrocks



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Figure 6 Cross section (profile) of line 1

Line 2 (Longitudinal pile location), this line is located parallel to line 1 start from west

to east. Total line length is 92 m, and lie generally east-west direction. There are 3 velocities

can be observed in this line, with V1 of top soil or overburden of 158-727 m/sec, V2 (second

layer) would be slightly weathered bedrocks with velocity of 928-1,672 m/sec, and V3 of about

2,238-4,227 m/sec which would be fresh or hard bedrock. Table 3 shows seismic velocity of

this spread. The thicknesses of these strata are varies and shown as cross section (or profile)

in figure 7




2 1,500 (928-1,672) Slightly weathered or fractured rocks

3 4,000 Fresh or Hard rocks



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Line 3 (Cross pile location), this line is located approximately perpendicular to line 1

and line 2, start from hillside down slope. Total line length is 34.5 m, and lie generally north-

south direction. Because of line is too short, there are only 2 velocities can be observed in this

line, with V1 of top soil or overburden of 210-823 m/sec, V2 (second layer) would be slightly

weathered bedrocks to basement rock with velocity of about 1,886-6,636 m/sec which would be

fresh or hard bedrock. In this line, there is step-like structure can be observed approximately in

the middle of line. Table 4 shows seismic velocity of this spread. The thicknesses of these

strata are varies and shown as cross section (or profile) in figure 8




2 3,000 (1,886-6,636) Fresh or Hard rocks



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For better understanding of weathering thickness and depth to basement rock

according to seismic velocity, the depth of each layer shown in profiles are used to construct

surface plot or 3D model of fresh or hard rock and surface of weathered rock overlying fresh

rock. The commercial computer package named ‘surfer’ is used and the result is shown infigure 9, 10 and 11.

Figure 9 Top of weathered rock plot



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Figure 10 Top of fresh/hard rock

Conclusion:The obtained results shown that there are 3 layers with vary in thickness those can be

recognized by seismic velocity. The loose overburden with velocity of not more than 1,000

m/sec is present over all survey lines. This would be backfill materials. The weathered /

fractured bedrock or decomposed rock layer is 1,500 m/sec in velocity and overlain by backfill

or top soil. The velocity of fresh or hard bedrock is more or less as high as 3,000- 4,000 m/sec

whereas lower for slightly weathered bedrock. The thickness of each layer is varies from about

1 m to more than 10 m.



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Figure 11 Surface plot of top of weathered and fresh rock



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Recommendation:

The seismic survey result shows low seismic velocities of geological materials which

are ranging from very loose top soil or backfill overburden. The thicknesses of these strata are

thin as only few meters on top of weathered rocks. The second layer is slightly weathered or

fractured rocks with its thickness more than that of top soil. The third layer which we expect to

encounter fresh/hard bedrock is of moderate to high seismic velocity (over 2,500 to 5,000

m/sec). There is no significant low velocity zone or layer in the result. The step-like feature

presents in line 3, but not shown on lines 1 and 2. High seismic velocities mean hard and high

strength rock. Drill hole data should be integrated and make correlation with seismic velocity for

better understanding rock property. Since there is step-like feature present under line 3, drill

hole data should be re-examined to ensure that there is no slip or crack along longitudinal pile

location.

Technical comments:

Due to heavy traffic all the time of investigation, the noise condition in the survey area

is very high. The suitable seismic source would be explosive or AWD; accelerated weight drop,

rather than sledge hammer which can generate limited signal strength. The quality of seismic

travel time in this data set is poor to fair to get sharp time reading. Moreover, field investigation

should be performed during noise-free period for better seismic signal.

……………………………..



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References:

Dobrin, M. B., 1976, Introduction to Geophysical Prospecting. McGraw Hill Book Co. Inc. N.Y.

Hawkins, L. V., 1961, The reciprocal method of routine shallow seismic refraction

investigations, Geophysics, vol. 26, pp. 806-819.

Redpath, B. B., 1973, Seismic refraction exploration for engineering site investigations.

Technical report no. E-73-4, U.S. Army Corp of Engineer Waterways Experiment

Station, Livermore, California.

Telford, W. M., Geldard, L. P., Sheriff, R. E. and Keys, D. A., 1976, Applied

Geophysics, Cambridge University Press, Cambridge, England.

………………………………….



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Appendices

-Reading travel t ime and T-X plot

-Seismic Profile of each spread

-Field operation photograph



Travel t ime and T-X plot

And

3D plot



T-X plot of Line 1



T-X plot of Line 2



T-X plot of Line 3



Cross section of Line 1









Contour plot of weathered rock surface



Contour plot of fresh rock surface



Surface plot of weathered and fresh rock surface



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Reading Travel time

Line 1Line 2Line 3

And

Point data for 3D plot



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Travel time of Line 1

LI NE 1 WATERFRONT CONDOMEDI UM PATTAYA

Geophone Shot station

station 0.0 22.0 46.0 70.0 92.0

0.0 11.0 19.5 28.0 35.0 45.5

4.0 16.0 21.0 29.5 37.0 47.0

8.0 19.5 25.0 38.5 44.5 55.0

12.0 17.0 16.0 28.0 35.5 46.0

16.0 17.5 10.0 24.5 33.5 44.020.0 21.0 9.5 25.5 35.0 45.0

24.0 19.5 3.0 20.5 30.0 40.5

28.0 24.0 10.0 22.5 31.5 42.5

32.0 24.5 14.5 20.5 30.5 41.0

36.0 26.5 19.0 16.5 28.5 39.5

40.0 27.5 21.0 14.5 28.0 39.5

44.0 28.0 24.0 6.5 27.0 38.0

48.0 29.5 25.5 6.5 26.5 38.0

52.0 33.5 29.0 14.5 28.5 40.5

56.0 34.5 29.5 19.5 26.0 38.560.0 37.0 33.0 22.5 23.0 37.5

64.0 36.0 31.0 22.0 13.5 33.5

68.0 37.5 34.0 24.5 8.5 33.0

72.0 36.0 31.5 23.5 6.5 27.5

76.0 39.5 34.5 27.0 16.0 28.0

80.0 40.0 36.0 29.5 20.5 23.0

84.0 46.5 41.5 33.0 24.5 20.0

88.0 45.5 39.5 33.5 27.5 12.5

92.0 46.5 42.0 39.0 32.5 7.3




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LI NE 2 WATERFRONT CONDOMEDI UM PATTAYA

Geophone Shot stationstation 0.0 22.0 46.0 70.0 92.0

0.0 10.0 30.0 38.0 45.5 53.0

4.0 20.5 29.5 38.0 43.5 52.5

8.0 24.0 29.5 38.0 42.5 52.5

12.0 25.5 25.5 37.5 40.0 52.0

16.0 28.5 24.5 37.0 40.0 51.5

20.0 29.5 14.5 37.0 42.0 49.5

24.0 29.5 13.5 36.0 39.0 48.0

28.0 28.5 22.0 32.5 35.5 46.0

32.0 31.5 29.0 32.0 35.0 46.5

36.0 35.0 30.5 30.5 38.0 47.0

40.0 37.5 32.0 27.0 38.5 45.0

44.0 37.0 35.0 13.0 37.0 45.5

48.0 37.5 36.5 13.5 35.0 43.5

52.0 39.5 37.0 26.5 33.5 42.0

56.0 42.5 36.5 32.0 30.5 42.0

60.0 37.0 33.5 28.5 23.0 35.0

64.0 42.5 38.0 33.0 15.0 34.5

68.0 41.5 41.0 35.0 14.0 33.5

72.0 44.0 41.5 37.0 14.0 30.0

76.0 43.0 41.5 36.0 16.0 30.0

80.0 44.0 41.0 38.0 23.5 27.5

84.0 46.5 46.5 39.5 27.0 24.5

88.0 44.5 44.5 40.5 29.0 23.0

92.0 52.5 47.0 42.0 29.5 7.5



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LI NE 3 WATERFRONT

CONDOMEDI UM PATTAYA

Geophone

station

Shot station

0.0 17.5 34.5

0.0 5.4 23.9 36.2

1.5 6.2 23.5 37.4

3.0 9.6 18.0 36.2

4.5 10.4 22.0 36.2

6.0 13.1 20.5 35.9

7.5 15.4 22.8 36.39.0 16.6 21.2 35.9

10.5 18.9 19.6 36.2

12.0 20.0 19.3 35.9

13.5 24.0 20.1 37.0

15.0 20.8 18.1 36.6

16.5 21.2 11.2 36.0

18.0 22.4 15.1 37.1

19.5 23.9 19.3 37.5

21.0 23.9 24.0 37.1

22.5 26.2 25.4 36.324.0 26.2 25.1 33.2

25.5 29.0 28.2 35.4

27.0 29.3 28.7 33.9

28.5 31.6 30.5 33.2

30.0 32.0 30.5 30.9

31.5 32.1 30.9 22.7

33.0 31.6 26.6 18.5

34.5 32.1 30.5 8.8



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Coordinate for 3D surface and contour plotPoints are from provided CAD file.(WF-pilelocation:01-02-12)

Easting, m Northing, m Z1

(soft rock),m

Z2

(hard rock),m

line 1 Lable

2945.88 5980.6 -3.5 -6 1

2949.83 5979.78 -3.5 -6.1 1

2953.79 5978.96 -3.5 -6.1 1

2957.74 5978.13 -3.4 -6.2 1

2961.7 5977.31 -2.5 -6.3 1

2965.65 5976.49 -2 -6.4 1

2969.6 5975.67 -2 -6.7 1

2973.56 5974.85 -2 -7.4 1

2977.51 5974.02 -2.5 -7.5 1

2981.47 5973.2 -2.5 -7.5 12985.42 5972.38 -2.5 -7.5 1

2989.37 5971.56 -2.5 -7.5 1

2993.33 5970.74 -2.6 -7.5 1

2997.28 5969.91 -2.7 -7.6 1

3001.23 5969.09 -2.8 -7.7 1

3005.19 5968.27 -2.9 -8.5 1

3009.14 5967.45 -3 -9 1

3013.1 5966.63 -3.4 -9.8 1

3017.05 5965.8 -3.4 -11 1

3021 5964.98 -3.4 -12.5 1

3024.96 5964.16 -3.4 -12.9 1

3028.91 5963.34 -3.5 -13.1 13032.87 5962.52 -3.5 -13.2 1

3036.82 5961.69 -3.5 -13.2 1

line 2

2944.4 5998.5 -4 -9 2

2948.35 5997.69 -4.1 -9.2 2

2952.29 5996.87 -4.2 -9.2 2

2956.24 5996.06 -4.3 -9.4 2

2960.19 5995.24 -4.3 -9.6 2

2964.14 5994.43 -4.3 -10 2

2968.08 5993.61 -4.3 -10.8 22972.03 5992.8 -4.3 -11 2

2975.98 5991.98 -4.3 -11.6 2

2979.92 5991.17 -4.5 -11.9 2

2983.87 5990.35 -5 -12 2

2987.82 5989.54 -5 -12 2

2991.76 5988.72 -5.1 -12 2

2995.71 5987.91 -5.2 -12 2

2999.66 5987.09 -5.1 -12.5 2

3003.61 5986.28 -4.9 -12.5 2

3007.55 5985.46 -4.9 -12.5 2

3011.5 5984.65 -4.8 -12.5 2

3015.45 5983.83 -4.8 -13 23019.39 5983.02 -4.7 -14 2



24

3023.34 5982.2 -4.6 -14.9 2

3027.29 5981.39 -4.7 -16 2

3031.23 5980.57 -4.6 -16 2

3035.18 5979.76 -4.6 -16 2

line 3

2991.8 5957.4 3

2992.08 5959.02 3

2992.35 5960.63 3

2992.63 5962.25 3

2992.9 5963.86 3

2993.18 5965.48 3

2993.45 5967.1 3

2993.73 5968.71 3

2994 5970.33 3

2994.28 5971.94 3

2994.55 5973.56 3

2994.83 5975.18 32995.1 5976.79 3

2995.38 5978.41 3

2995.65 5980.02 3

2995.93 5981.64 3

2996.2 5983.26 3

2996.48 5984.87 3

2996.75 5986.49 3

2997.03 5988.1 3

2997.3 5989.72 3

2997.58 5991.34 3

2997.85 5992.95 3

2998.13 5994.57 3



35

Field activity photograph



36

Survey line location checking

Equipment setup, along staking line



37

Equipment setup, ready for data acquisition

Seismograph module; GEODE-24 (yellow), seismic cable; orange



38

Geophone; red color, connected to seismic cable

Close look of geophone; connected to cable via clip

Documents

Waterfront Seismic Survey Report