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POSIVA OY FI-27160 OLKILUOTO, FINLAND Tel +358-2-8372 31 Fax +358-2-8372 3709 Ida Öhman Eero Heikkinen Tomas Lehtimäki December 2006 Working Report 2006-114 Seismic 2D Reflection Processing and Interpretation of Shallow Refraction Data

Seismic 2D Reflection Processing and Interpretation of Shallow

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Page 1: Seismic 2D Reflection Processing and Interpretation of Shallow

P O S I V A O Y

FI -27160 OLKILUOTO, F INLAND

Tel +358-2-8372 31

Fax +358-2-8372 3709

I da Öhman

Eero He ikk inen

Tomas Leht imäk i

December 2006

Work ing Repor t 2006 -114

Seismic 2D Reflection Processing andInterpretation of Shallow Refraction Data

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December 2006

Working Reports contain information on work in progress

or pending completion.

The conclusions and viewpoints presented in the report

are those of author(s) and do not necessarily

coincide with those of Posiva.

I da Öhman

Eero He ikk inen

Tomas Leht imäk i

Pöyry Env i ronment Oy

Work ing Repor t 2006 -114

Seismic 2D Reflection Processing andInterpretation of Shallow Refraction Data

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Seismic 2D Reflection Processing and Interpretation of Shallow Refraction Data

ABSTRACT

Posiva Oy takes care of the final disposal of spent nuclear fuel in Finland. In year 2001 Olkiluoto was selected for the site of final disposal. Currently construction of the underground research facility, ONKALO, is going on at the Olkiluoto site.

The aim of this work was to use two-dimensional reflection seismic processing methods to refraction seismic data collected from the ONKALO area in year 2002, and to locate gently dipping reflectors from the stacked sections.

Processing was done using mainly open source software Seismic Unix. After the processing, the most distinct two-dimensional reflectors were picked from seismic sections using visualization environment OpendTect. After picking the features from crossing lines were combined into three-dimensional surfaces. Special attention was given for the detection of possible faults and discontinuities. The surfaces were given coordinates and their orientation was adjusted using a geometric procedure, which corresponds roughly a 3D migration, transferred to 3D presentation utility and compared to available geological information.

The advantage of this work is to be able to get three-dimensional reflection seismic results from existing data set at only processing costs. Survey lines are also partly located in ONKALO area where extensive surface seismic surveys may not be possible to perform.

The applied processing method was successful in detecting the reflectors. Most significant steps were the refraction and residual statics, and deconvolution. Some distinct reflectors can be seen at times 20-200 ms (vertical depths 50...500 m). The signal gets noisier below 200 ms. Reflectors are best visible as coherent phase between the adjacent traces, but do not raise much above the surrounding noise level. Higher amount of traces to be stacked would emphasis the reflections and their continuity more.

Reflectors picked on crossing lines match well to borehole observations (KR4, KR7, KR24 and KR38) of fracture zones, and get support from geological and hydrological models of the site. The observed reflections coincide with fracturing intensity and P-wave velocity minima from boreholes. Reflections coincide also rather well to the separate 3D seismic results from overlapping area.

The results demonstrate that seismic measurements intended for refraction interpretation can also be successfully processed using reflection seismic processing methods. Increasing number of active geophones and shots, and line density, would enhance reliability of the reflections.

Keywords: Seismic, reflection, refraction, processing, interpretation, crystalline, bedrock, migmatite, fracture zone, spent nuclear fuel, geological disposal

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Seismisen refraktiomittauksen 2D reflektioprosessointi ja tulkinta

TIIVISTELMÄ

Posiva Oy vastaa radioaktiivisen ydinjätteen loppusijoituksesta Suomessa. Vuonna 2001 Olkiluoto valittiin ydinjätteiden loppusijoituspaikaksi. Parhaillaan Olkiluotoon raken-netaan ONKALOA, maanalaista tutkimustilaa.

Tämän työn tarkoituksena on prosessoida ONKALO-alueelta vuonna 2002 kerättyä refraktioseismistä dataa käyttäen heijastusseismiikkaa varten kehitettyjä prosessointi-menetelmiä, sekä tulkita pinotuista sektioista loivakaateisia heijastajia.

Prosessointi suoritettiin käyttäen pääasiassa vapaan lähdekoodin ohjelmaa Seismic Unix. Prosessoinnin jälkeen selvimmin erottuvat kaksiulotteiset heijastajat poimittiin seismisistä vertikaalileikkauksista OpendTect-ohjelmalla. Poiminnan jälkeen risteävien linjojen heijastuspiirteitä yhdistettiin kolmiulotteisiksi pinnoiksi. Poiminnassa kiinni-tettiin erityisesti huomiota mahdollisiin siirroksiin ja epäjatkuvuuksiin. Pinnoille laskettiin koordinaatit ja tehtiin asentokorjaus käyttäen menetelmää, joka vastaa kar-keasti 3D-migraatiota (Paulamäki et al. 2006). Migratoidut pinnat siirrettiin ohjelmaan, jossa ne voitiin esittää kolmiulotteisesti, ja niitä verrattiin olemassa olevaan geologiseen informaatioon.

Työn etuna on se, että heijastusseismisiä 3D-tuloksia saadaan olemassa olevasta refraktiodatasta pelkin prosessointikustannuksin. Mittauslinjat sijaitsevat osittain alueel-la, jolla laajoja seismisiä mittauksia ei enää ole mahdollista suorittaa, joten jo olemassa olevan datan hyödyntäminen on tärkeää.

Käytetyllä prosessointimenetelmällä onnistuttiin tulkitsemaan heijastajat. Tärkeimmät työvaiheet olivat refraktio- ja residuaalinen staattinen korjaus sekä dekonvoluutio. Joita-kin selviä heijastuksia nähdään 20 – 200 ms aikavälillä (50 – 500 m vertikaalisyvyys). Signaalin kohina voimistuu 200 ms jälkeen. Heijastukset havaitaan parhaiten koherentin vaiheen perusteella vierekkäisten kuvaajien välillä, koska amplitudi ei kohoa paljoa ympäristön kohinatason yläpuolelle. Suurempi pinoamisen kertaluku vahvistaisi heijas-tuksia ja niiden jatkuvuutta.

Risteäviltä linjoilta poimitut heijastajat osuvat hyvin yhteen kairanreikähavaintojen (KR4, KR7, KR24 ja KR38) rikkonaisuusvyöhykkeiden kanssa, ja saavat tukea geologisista ja hydrologisista malleista. Heijastukset korreloivat kasvaneen, rei’istä havaitun rakotiheyden ja seismisen P-aallon minimien kanssa. Samoin yhteensopivuus on hyvä erillisten 3D-heijastustulosten kanssa päällekkäiseltä alueelta.

Tulokset osoittavat että refraktiotulkintaa varten tehtävä seisminen mittaus kannattaa suunnitella siten, että myös reflektioprosessointi on mahdollinen. Lisäämällä aktiivisten geofonien ja lähdepisteiden määrää sekä linjatiheyttä heijastukset nähdään luotetta-vammin.

Avainsanat: Seisminen, heijastus, taittuminen, käsittely, tulkinta, kiteinen peruskallio, migmatiitti, rikkonaisuusvyöhyke, käytetty ydinpolttoaine, geologinen loppusijoitus

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TABLE OF CONTENTS

ABSTRACT

TIIVISTELMÄ

1 INTRODUCTION .............................................................................................. 3

2 SOURCE DATA................................................................................................ 5

2.1 Surface seismic data............................................................................. 5

2.2 Background information ........................................................................ 8

3 DATA PROCESSING ....................................................................................... 9

4 INTERPRETATION......................................................................................... 29

4.1 Two dimensional reflectors ................................................................. 29

4.2 Three dimensional surfaces ................................................................ 30

4.3 Comparison to borehole data.............................................................. 33

5 CONCLUSIONS.............................................................................................. 41

REFERENCES ........................................................................................................... 43

APPENDIX 1. STACKED SEISMIC SECTIONS AND PICKED REFLECTORS. ....... 45

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1 INTRODUCTION

Posiva Oy takes care of the final disposal of spent nuclear fuel in Finland. In year 2001 Olkiluoto was selected for the site of final disposal. Currently construction of an underground research facility, ONKALO, is going on at the Olkiluoto site. Suomen Malmi Oy has carried out shallow refraction seismic surveys in 2001 and 2002 in order to determine the overburden thickness and to study seismic P-velocity on bedrock surface and to locate e.g. possible fracture zones (Ihalainen 2003). In year 2001 survey lines from S1 to S27 were measured (15,4 km in total) and in year 2002 survey lines from S27 to S69 (17,57 km in total).

The aim of this work was to use two-dimensional reflection seismic processing methods to refraction seismic data collected from the ONKALO area, and to locate gently dipping reflectors from the processed survey lines.

Processing applied open source software Seismic Unix (SU) (Stockwell & Cohen 2002). Processing included reading and re-arranging the data set, removal of noisy traces, geometric spreading correction, bandpass filtering, refraction and residual statics, deconvolution, airwave muting, automatic gain control, normal moveout and stacking. The goal was to find the best possible processing parameters for the seismic data set. The refraction measurement array is not optimized for reflection processing which leads to quite small 2D fold, approximately only 4, which makes the processing a demanding task.

After the processing two-dimensional reflectors will be picked in 3D visualization environment and combined into three-dimensional surfaces. Special attention will be given for the detection of possible faults and discontinuities.

The advantage of this work is to be able to get three-dimensional reflection seismic results from existing data set at only processing costs. Survey lines are also partly located in ONKALO site where extensive surface seismic surveys may not be possible to perform and therefore the effective exploration of existing data is important.

The work was conducted on Posiva’s commission, order number 9742/06/TUAH. Contact person on Posiva side was Mr. Turo Ahokas. Processing and reporting was carried out by Ms. Ida Öhman of Pöyry Environment. Techniques were discussed through with and advised by Dr. Christopher Juhlin of Uppsala University, Dr. Calin Cosma and Mr. Mircea Cozma of Vibrometric and Mr. Tomas Lehtimäki and Mr. Eero Heikkinen of Pöyry Environment. Mr. Lehtimäki organised the raw data and computed the geometric conversion of picked surfaces. Mr. Jorma Nummela of Pöyry Environment converted the surfaces into AutoDesk and Surpac Vision 3D visualisation software.

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2 SOURCE DATA

2.1 Surface seismic data

Original refraction seismic data was collected from Olkiluoto during the summer and autumn 2002 (Ihalainen 2003). Survey was carried out by Suomen Malmi Oy (Smoy). Data consists of 17 570 m of refraction seismic survey lines named S28-69. Lines S1 – S27 of 2001 were recorded to 102,4 ms and were not considered in this work.

Original aim for the refraction field survey has been to determine the seismic velocities in the bedrock surface, using refraction intercept time and generalised reciprocal (GRM) interpretation techniques on 2D lines. The interpretations were further examined and merged onto maps of soil thickness and velocity (Lehtimäki 2003).

Table 1 displays the information about the survey lines selected for the seismic processing. The lines have been surveyed parallel on two directions (E-W and N-S) and mainly at 100 m line spacing. Location of the lines is shown in Figure 1. Lines for the seismic processing were selected to get the best possible coverage of the ONKALO area within the available time schedule.

Table 1. Refraction seismic survey lines selected for the seismic processing. Coordinates are locations for the first and last common mid points and length distance between these points.

Line name Northing start Easting start Northing end Easting end Length m

28 6791770 1525650 6792010 1525650 240 282 6791995 1525650 6792230 1525650 235 29 6791727,5 1525700,00 6791980 1525700 252,5 30 6791800 1525750 6791950 1525750 150 302 6791920 1525750 6792250 1525750 330 31 6791770 1525800 6791920 1525800 150 312 6791900 1525800 6792230 1525800 330 32 6791740 1525850 6791890 1525850 150 322 6791890 1525850 6792232,5 1525850 342,5 33 6791830 1525950 6792250 1525950 420 34 6791795 1526050 6792137,5 1526050 342,5 342 6792047,75 1526050 6792230 1526050 182,25 35 6791805 1526150 6792292,5 1526150 487,5 362 6791960 1526250 6792192,5 1526250 232,5 372 6792030 1526300 6792170 1526300 140 43 6791950 1525490 6791950 1525730 240 432 6791950 1525720 6791950 1526230 510 44 6792000 1525500 6792000 1525650 150 442 6792000 1525655 6792000 1525790 135 443 6792000 1526130 6792000 1526280 150 45 6792050 1525547,5 6792050 1526330 782,5 46 6792100 1525480 6792100 1525900 420 47 6792150 1525340 6792150 1526390 1050 48 6792250 1526030 6792250 1526170 140 50 6792381,32 1526028,9 6792146,76 1526261,02 234,56

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Figure 1. Locations of the refraction seismic survey lines (red) in Table 1.

Length of each 24-channel geophone array was 90 meters (Figure 2). The geophone spacing was 5 meters but at the both ends and in the middle of an array it was supplemented to 2,5 meters.

Dynamite (35%) charges of 15-120 g were used as seismic source. The number of shots for each array was nine, of which four were in-line offset shots 30-120 meters outside the array and the rest at the both ends and in the middle of an array. Distances between the shotpoints varied from 20 to 30 meters.

Line number 342 was surveyed using one meter geophone spacing and eleven shotpoints on each 24 m long array.

Recording was done using type 10B, 4,5 MHz vertical geophones with 374 Ohm reel manufactured by Mark Product’s (Houston, USA) (Ihalainen 2003). Acquisition was carried out with ABEM Terraloc Mk VI seismograph. Sampling interval was 25 µs. More detailed description of the field layout and equipment can be found in the references Ihalainen (2003).

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Figure 2. Survey array. At the line 342 geophone spacing was 1 meter and the number of shots 11.

Seismic data was recorded to 409,6 ms (Figure 3 and Figure 4). Quality of the stacked data is quite good down to 200 ms but after that it gets noisier. Quality of the data also varies substantially from line to line as can be seen from Figure 3 and Figure 4. For example lines S33 and S34 are located over a rocky outcrop and due to that the data is quite noisy and therefore harder to process with uniform work flow settings. As can be seen in Figure 3, in good data for example first arrivals (P-wave), S-wave and airwave are easily detected. In the case of a noisy data (Figure 4) this is a lot harder.

Figure 3. Example of a good data set after removing the noisy traces, shot gather. First P arrival is clear. Also S wave and airwaves are seen. First four shots from the line 30. AGC has been performed. Trace number on X-axis and two way travel time in seconds on Y-axis.

P

S

Airwave

Shot 1 Shot 2 Shot 3Shot 4

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Figure 4. Example of a noisy data set after removing the noisy traces, shot gather. First four shots from the line 34. AGC has been performed. Trace number on X-axis and two way travel time in seconds on Y-axis.

2.2 Background information

The processed and interpreted seismic results were compared and validated to set of existing knowledge on the site.

The seismic velocities and signal frequency range have been investigated in preceding seismic VSP works (Enescu et al. 2004). Distribution of velocity data and velocity anomaly locations in boreholes have been extracted from borehole geophysical logging, e.g. Julkunen et al. (2004), Lahti & Heikkinen (2005). Petrophysical properties of Olkiluoto lithology, and the elastic contrasts, were considered during prior modelling by Mr. Tomas Lehtimäki (Saksa 2006, in preparation) for geometrical observability, frequency range and attenuation; and by Dr. Christopher Juhlin in Uppsala for considerations of, e.g., stacking fold and signal to noise ratio.

Geometrical information on potentially reflecting bedrock features have been reviewed from bedrock model descriptions. These include features interpreted on basis of hydrological model data (Ahokas & Vaittinen 2007), geological observations (Paulamäki et al. 2006), and interpretations based on multidisciplinary bedrock property classifications (Vaittinen et al. 2003). Results can be also directly compared and reviewed against VSP and 3D seismic interpretations on the site (Enescu et al. 2004, Juhlin & Cosma 2006).

P

S

Airwave

Shot 1 Shot 2 Shot 3 Shot 4

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3 DATA PROCESSING

The aim was to perform reflection seismic processing for two-dimensional seismic lines, surveyed originally for refraction seismic interpretation. Advantage of this work is to get three-dimensional reflection seismic results from the existing data at only processing costs. Processing was based on a processing flow of SKB studies presented in Juhlin et al. (2001, 2004) and testing of processing to data set of this report for line S28, performed by Dr. Christopher Juhlin in Uppsala (December 2005).

After processing the seismic sections were interpreted in order to map the orientation, continuity, location and shape of subhorizontal 3D reflectors as well as to locate possible subvertical faults.

Before seismic interpretation the survey data must be carefully processed. The processing steps are presented in Table 2. Line S28 is used here to exemplify the processing steps (see processing flow in Table 2). Practically no reflectors can be seen in the raw data from the line S28, shown in Figure 5. After filtering and stacking, normally some discontinuous traces of reflections can be estimated. Even though automatic gain control (AGC) is applied to data at the end of processing, it has been applied to images in order to make the visualization more illustrative. AGC improves visibility of late-arriving events in which attenuation or wavefront divergence has caused amplitude decay.

The most important processing steps to bring the reflections visible were refraction statics and deconvolution. The goal was to find the processing parameters that could be easily and quickly applied to the whole seismic data set.

Refraction static corrections will remove the differences of travel times in first arrival, caused by differences in elevation and near surface velocity variation in soil and weathered layers. Deconvolution will sharpen the signal signature and remove multiple waves from reflections. During deconvolution, adding noise serves also as frequency equalization (spectral whitening).

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Figure 5. Raw shot gather from the line S28 with automatic gain control. First nine shots on line. Trace number on X-axis and two way travel time in seconds on Y-axis.

Table 2. Processing flow and parameters.

Processing step Parameters

1. Convert SEG2 data into SEGY (Figure 5)2. Remove noisy traces 3. Set geometry 4. Geometric spreading correction Multiply by

5,1t5. Bandpass filter (Figure 8) 30-60-400-600 Hz 6. Refraction statics (Figure 11)7. Set CDP numbers 8. Deconvolution (Figure 12) Minlag: 0,01ms

Maxlag: 40 ms Start of autocorrelation: 0 offset: 100 ms; max offset: 120 s End of autocorrelation: 0 offset: 300 ms; max offset: 400 ms Noise: 1 %

9. Bandpass filter 0-100 ms: 70-140-300-450 Hz 50-200 ms: 60-120-300-450 Hz 150-500 ms: 50-100-270-400 Hz

10. Mute (Figure 14) Linear velocity: 340 m/s Width: 0 offset: 10 ms; max offset: 15 ms Taper before hard mute: 1000 samples

11. Automatic Gain Control (AGC) Window: 50 ms 12. Residual statics (Figure 16)13. Normal Moveout (NMO) (Figure 17) Velocity: 5000 m/s

Stretch mute: 4 Number of points to taper: 1000

14. Stack (Figure 21 a) )

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Processing was performed using free seismic data processing package Seismic Unix(SU) (Stockwell & Cohen 2002). Refraction seismic data SEG-2 format was converted into SEG-Y format before importing into SU (Table 2, item 1), using shareware software IXseg2segy (Interpex Ltd). Number of samples in SEG-2 format was limited, and conversion was preferred rather than down sampling. In down sampling some features of the data could have been lost.

Bad traces to be removed (Table 2, item 2) were selected visually using ReflexWsoftware (ReflexW) and then removed in SU. Typically these geophones are located near the shots or the geophones were not properly mounted into the ground.

The next step after removing the noisy traces was setting the geometry (Table 2, item 3). As described in Chapter 2 the geophone spacing and shot spacing are irregular. Line number S28 consists of 432 seismic traces and for each trace, trace number, shot number, geophone number, shot position, geophone position, common depth point (CDP) position and offset must be set. Common depth point is a common reflecting point at depth on a reflector (see Figure 6). In the case of planar layers, CDP is a halfway point between a source and a receiver as illustrated in Figure 6. In this work the CDP locations have been computed assuming that reflectors are planar. Geometry was read from the ASCII file, which was created with Microsoft Excel, and applied to data using Seismic Unix. Example of geometry file is shown in

Figure 6. Definition of a common depth point in the case of a planar reflector.

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Table 3. Example of a geometry file from the line 28. First 12 traces.

Tracenumber

Shotnumber

Geophone number

Shotposition m

Geophone position m

CDPposition m Offset m

1 1 1 -60 0 -30 60

2 1 2 -60 2,5 -28,75 62,5

3 1 3 -60 5 -27,5 65

4 1 4 -60 7,5 -26,25 67,5

5 1 5 -60 12,5 -23,75 72,5

6 1 6 -60 17,5 -21,25 77,5

7 1 7 -60 22,5 -18,75 82,5

8 1 8 -60 27,5 -16,25 87,5

9 1 9 -60 32,5 -13,75 92,5

10 1 10 -60 37,5 -11,25 97,5

11 1 11 -60 42,5 -8,75 102,5

12 1 12 -60 45 -7,5 105

Geometric spreading correction (Table 2, item 4) was applied to seismic data by multiplying amplitude data by 5,1t . Selection of parameter was based on a testing and references (Juhlin et al. 2004). Data was filtered (Table 2, item 5) using zero-phase, sine squared tapered band pass filter (Stockwell & Cohen 2002) with the following parameters.

lower cutoff frequency: 30 Hz lower plateau frequency: 60 Hz upper plateau frequency: 400 Hz upper cutoff frequency: 600 Hz

Purpose of this preliminary filtering was to remove the highest and the lowest frequencies. Selection of parameters was based on a raw spectrum. Example of a spectrum from the line S28 is shown in Figure 7. The frequency varies from very low to very high frequencies. Shot gather after the preliminary filtering is shown in Figure 8. Reflectors are not yet visible.

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Figure 7. Original spectrum from the line S28. Traces 297-363. Selection of parameters for preliminary filtering was based on this spectrum in order to remove the highest and lowest frequencies.

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Figure 8. Shot gather from the line S28 after the preliminary filtering with automatic gain control. First nine shots. Trace number on X-axis and two way travel time in seconds on Y-axis.

Refraction static corrections (Table 2, item 6) were calculated using Microsoft Excel and were applied to data after the preliminary filtering. Values of static corrections must be integers in milliseconds. The purpose of the refraction static corrections was to eliminate the effect of the weathering layer and the surface elevation variations (see Figure 9). Refraction statics calculation was based on a first P-wave direct arrival times (first breaks, see Figure 3). Refracted first breaks represent the base of a weathering layer.

Figure 9. Refraction static corrections eliminate the effect of the weathering layer and the surface elevation variations. Arrows represent the value of correction applied to trace located between the shot and the receiver.

The static error was removed from each trace by computing the theoretical first breaks using the replacement velocity of 5000 m/s and trace offset. Correction was obtained by subtracting theoretical first break from observed first break. After applying refraction static corrections to seismic data, the base of weathering layer becomes a

SURFACE

SHOT

RECEIVER

v = 5000 m/s

WEATHERING LAYER

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new datum and elevation differences between the shot and the geophone and between the geophones are eliminated (Figure 9). Because depth of the real weathering layer may vary from trace to trace, some differences between the shots might still remain. We can estimate that these variations are approximately +/- 2 m based on a previous interpretations (Ihalainen 2003, Lehtimäki 2003), which leads to +/- 0,8 ms error in two way travel times using the replacement velocity of 5000 m/s. This is acceptable, because the average amplitude among the traces is many times greater than this error and because error is smaller than the 1 ms resolution of refraction static corrections.

Another problem caused by this approach to refraction statics, is unknown datum, because there is no information about the thickness of the weathering layer or low velocity volumes near surface. These may be defined using ray-tracing inversion of first breaks. In practice the applied procedure led to adequate accuracy of the result.

Comparison between stacked sections with and without refraction static corrections (Figure 20 a) and Figure 20 b) and Figure 22 and Figure 24) indicates that the approach is easy and fast and therefore adequate and reasonable to perform. Example of a shot gather before and after the refraction statics is shown in Figure 10 and Figure 11.

Figure 10. First three shots with AGC from the line S28 after the preliminary filtering but without refraction statics. Trace number on X-axis and two way travel time in seconds on Y-axis.

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Figure 11. First three shots with AGC from the line S28 after the preliminary filtering and refraction statics. Trace number on X-axis and two way travel time in seconds on Y-axis.

Deconvolution (Table 2, item 8) applied Wiener predictive error filtering. Aim was to recover high frequencies, attenuate multiples, equalize amplitudes, produce a zero-phase wavelet and generally affect the wave shape. Deconvolution was performed using the following parameters and is one of the most important processing steps.

First lag of prediction filter: 0,0001 s Operator length: 0,040 s Start of autocorrelation window: min offset 0,1 s, max offset 0,12 s End of autocorrelation window: min offset 0,3 s, max offset 0,4 s Noise: 1 %

Stacked sections were compared with and without deconvolution in Figure 21 a) and Figure 21 b), respectively. Figures indicate the effect of deconvolution. After the deconvolution the data was filtered (Table 2, item 9) with similar filter as before deconvolution, using parameters shown below.

0-100 mslower cutoff frequency: 70 Hz lower plateau frequency: 140 Hz upper plateau frequency: 300 Hz upper cutoff frequency: 450 Hz

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50-200 ms lower cutoff frequency: 60 Hz lower plateau frequency: 120 Hz upper plateau frequency: 300 Hz upper cutoff frequency: 450 Hz

150-500 mslower cutoff frequency: 50 Hz lower plateau frequency: 100 Hz upper plateau frequency: 270 Hz upper cutoff frequency: 400 Hz

Shot gather after the deconvolution and the second filtering is shown in Figure 12.Now the reflectors after 130 ms and 200 ms are seen. It is hard to see these reflectors in the shot gathers where the shot point is located between the geophones because of the airwave.

Figure 12. Shot gather from the line S28 after deconvolution and second filtering with AGC. Reflectors can be seen under 130 ms and 200 ms marked with red and blue arrows respectively. Airwave is marked with orange arrow. Trace number on X-axis and two way travel time in seconds on Y-axis. First 6 shots on line.

The behaviour of records according to shot offset was viewed in common offset gathers (Figure 13). The airwave (red line) was removed by muting (Table 2, item 10) at velocity 340 m/s vs offset. The air blast duration was set as a function of offset. Number of points to taper before hard mute was set to 1000. Common offset gather

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after the muting is shown in Figure 14. After the muting automatic gain control (AGC) was applied (Table 2, item 11) to data in order to improve visibility of late-arriving events in which attenuation or wavefront divergence has caused amplitude decay.

Figure 13. Offset gather from the line S28. Airwave with the velocity of 340 m/s is marked with red line.

Figure 14. Common offset gather from the line S28 after muting.

The calculated refraction statics were quite good on basis of lining up of P-arrival (see Figure 12). Some residual errors still remain, which must be corrected for. These errors can be seen after deconvolution as displacements in first breaks and the reflected events. The residual statics (Table 2, item 12) are plus-minus errors with respect to the long wavelength trend of travel time anomalies due to the near-surface effects (Li 1999). Corrections were applied to traces by picking the first break maxima and computing their differences to the theoretical first breaks, which were computed during the refraction statics.

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Original first breaks were picked to zero amplitude (crossover). This work applied maximum amplitude, so datum was shifted half a wavelength (2-3 ms). After this shift, datum was 0 m +/- 2 m. This is because before the residual statics datum was 5 m +/- 2 m which corresponds to 2 ms shift in two way travel time. In Figure 15 is shown a shot gather and in Figure 20 b) a stacked section before the residual statics and in Figure 16 a shot gather and in Figure 21 a) a stacked section after the residual statics (see also Figure 23 and Figure 24).

Residual statics makes the reflecting events clearer and straighter. Residual statics were not applied to the data from the survey lines S33 and S34 because reliable picking of first break maxima was not possible due to noisy data (see Figure 4).

Figure 15. Shot gather from the line S28 after the muting but before residual statics. Trace number on X-axis and two way travel time in seconds on Y-axis. First 4 shots on line.

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Figure 16. Shot gather from the line S28 after the muting and residual statics. Trace number on X-axis and two way travel time in seconds on Y-axis. First 4 shots. Reflections can be seen e.g. at 013 and 0.2 seconds.

Normal moveout (NMO, Table 2, item 13) compensates for the effects of the separation between seismic sources and receivers and must be performed prior to stacking. NMO velocity used was 5000 m/s and stretch mute 4. Samples with NMO stretch exceeding stretch mute were zeroed. Shot gather after the normal moveout is shown in Figure 17. In Figure 18 is shown a detailed example of the first shot from the line S28. Originally first breaks and reflecting events are hyperbolic but NMO straightens them up.

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Figure 17. Shot gather from the line S28 after the normal moveout. Trace number on X-axis and two way travel time in seconds on Y-axis. First 4 shots.

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Figure 18. First shot from the line S28 before and after NMO. Red line demonstrates how NMO straightens up first breaks.

After NMO data can be stacked (Table 2, item 14). First it must be sorted into common depth point gathers, which means that data is sorted by its CDP position, and CDP positions must be changed into CDP numbers. Traces with the same CDP number are stacked. CDP numbers are integers and calculated based on a position of each CDP. All traces having their CDP position within a bin length are stacked into the fold. Length of a bin was 2,5 meters and consequently maximum fold is eight and minimum fold one. Figure 19 demonstrates principle of stacking. In the line 342 geophone spacing was smaller so bin is 1 meter. Each stacked sample is divided by the square root of non-zero values stacked. Final stacked section from the line S28 is shown in Figure 21 a). Only the first 300 ms of the data are displayed because of a low signal-to-noise ratio in the lower parts of the data.

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Figure 19. a) Traces before stack b) Same traces after stack. Six traces within 2,5 m bin (red and green lines in figure a) ) are stacked. Corresponding stacked traces are marked with red and green arrows in figure b). In reality CDP positions are not equally spaced and therefore fold varies.

a) CDP position b) CDP number

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Figure 20. a) Stacked section without refraction and residual statics from the line S28 down to 300 ms. CDP number on X-axis and two way travel time in seconds on Y-axis. b) Stacked section without residual statics from the line S28 down to 300 ms. CDP number on X-axis and two way travel time in seconds on Y-axis.

a) b)

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Figure 21. a) Final stacked section from the line S28 down to 300 ms using a wiggle trace display. CDP number on X-axis and two way travel time in seconds on Y-axis. b) Stacked section without deconvolution from the line S28 down to 300 ms. CDP number on X-axis and two way travel time in seconds on Y-axis.

a) b)

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Figure 22. Stacked section without refraction and residual statics from the line S342 down to 300 ms. CDP number on X-axis and two way travel time in seconds on Y-axis.

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Figure 23. Stacked section without residual statics from the line S342 down to 300 ms. CDP number on X-axis and two way travel time in seconds on Y-axis.

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Figure 24. Final stacked section from the line S342 down to 300 ms using a wiggle trace display. CDP number on X-axis and two way travel time in seconds on Y-axis.

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4 INTERPRETATION

After the seismic processing has been performed for the selected set of refraction seismic survey lines, data was interpreted. First step was to examine two dimensional stacked sections, which can be found from the APPENDIX 1, and to locate possible reflectors. After this, two-dimensional stacked sections were imported into the visualization environment OpendTect (OpendTect 2006) and reflectors were picked in 3D.

4.1 Two dimensional reflectors

Two dimensional seismic data from the survey lines shown in Figure 1, was processed using the processing parameters in Table 2. The result was a set of stacked seismic sections which can bee seen in APPENDIX 1 using variable density display. These two-dimensional sections can be used to locate the reflectors but the actual picking is done in 3D. Taking a closer look at the reflector below 130 ms in lines S28, S29, S30 and S31, it can be seen continuing from line to line. Very clear reflectors can be seen in several lines but for example in line S47 only few weak ones are seen. Reflectors are mostly found from the upper parts of the seismic sections. This is due to the lower signal-to-noise ratio (see shot gathers, Figure 5) in the later times of the data (greater depths). This can also be seen from the stacked sections (see APPENDIX 1). Two-dimensional reflectors are shown in APPENDIX 1.

Some reflectors may not appear to be very clear in first place, and may be hard to detect from individual lines. Different image colour settings, aspect ratios and scales were applied. Picking in 3D allows locating reflectors on adjacent and crossing lines, which helps to recognise continuous reflecting events. In Figure 25 (Lines 48, 50 and 362) the reflectors are marked with red arrows.

In APPENDIX 1 scale is 1:5000 in order to display data more clear. Picking was easier with stretched X dimension in 3D.

Depth of the reflectors is determined using the approximate velocity of 5000 m/s. The velocities used in static correction and NMO give a generic idea on the real velocities in bedrock. However the true velocity has to be confirmed using velocity fitting on diffractions seen on seismic sections, from external sources (VSP data and 3D reflection data) and with using a borehole control. Processing has applied a phase consistent (zero phase) work flow. Correctness of depth axis will rely on recognition of correct phase of the reflected arrival, e.g. ¼ - ½ wavelength late picks will mean approx. 5-10 m too deep depth level or the reflection. Selecting the velocity e.g. either 5000 m/s, or 5500 m/s, will lead to approx. 10% error in the depth axis.

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Figure 25. Example of a weak reflector continuing from line S48 to line S50 to line S362. It would be hard to locate the reflector from the single lines without the help from the crossing lines.

4.2 Three dimensional surfaces

Two-dimensional stacked sections were imported into OpendTect visualization environment, where reflectors were picked. Sections were displayed using variable density display. In an intersection of two lines, reflectors may continue from line to line which allows three dimensional picking. Example of reflectors continuing from line to line is shown in Figure 26. Reflectors picked from crossing lines, construct surfaces. After all the relevant surfaces and reflectors were picked, they were merged into larger surfaces. Still some single two-dimensional reflectors remain.

Example of a three-dimensional surface is shown in Figure 27. This surface consists of reflectors picked from the lines 312, 432, 28, 29, 30, 31 and 43.

Twelve surfaces and 23 single 2D reflectors in total were picked and are shown in APPENDIX 1. 2D reflectors constructing surfaces are named according to the surface name and single reflectors with a prefix ‘single’. Surfaces were mainly in focus but also some single reflectors can be found interesting (see below). Normally the high amplitude reflectors are not continuous over the whole survey area, but display rather broken and some times discontinuous character. Also abundant diffracted energy (steep

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events) indicates presence of offsetting or terminating structures. Steep events are mostly seen on ca. 1400-1600 m/s velocities (Stoneley waves), some residuals of airwave can be seen, too (340 m/s). Some diffracted P or S-waves are also seen on some locations. F-K filtering at -2000 …0…+2000 m/s window remove these events and make the S/N ratio of deeper sections better.

Figure 26. Intersection of lines S45 and S322. Reflectors continue from line to line and are marked with arrows.

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Figure 27. Three-dimensional surface picked from the lines S312, S432, S28, S29, S30, S31 and S43.

The time picked surfaces, recognised from several parallel and crossing lines, were corrected for offset and offline reflection geometry. The original picks are displayed on the sections with their apparent dips (see APPENDIX 1). The observations are geometrically tilted so, that the shortest distance from CDP is measured along the normal of the reflection plane (reflector is tilted towards the up-dip direction). This corresponds roughly a 3D migration, but is a simplified procedure (Prissang et al. 2004). Table 4 shows the information on the corrected surfaces. Surfaces are displayed in Figure 28.

In Figure 44 in APPENDIX 1 is shown an interesting breakout and discontinuity of a reflecting surfaces ref 9 and ref 10, indicating possible vertical displacement along a subvertical fault. The apparent diffracted velocities near the event match to Stoneley arrivals.

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Table 4. Positions and dips for migrated three dimensional surfaces

Surface

name

Dip direction/ Dip

(degrees from North

and Horizontal)

Two way

travel time

(ms)

Depth (m) Picked from the lines

ref 1 134,30 N/ 16,18 416 -723,8…-623,3 48, 50, 362, 372ref 2 275,16 N/ 63,91 178 -199,8…-131,2 50, 362ref 3 140,32 N/ 18,79 322 -284,5...-251,5 342, 47ref 5 130,87 N/ 11,51 421 -333,7...-273,9 312, 432, 28, 29, 30, 31, 43ref 6 109,62 N/ 33,59 374 -499,0...-419,2 28, 29, 29, 30ref 7 89,22 N/ 10,66 344 -205,8...-162,5 28, 29ref 8 147,09 N/ 8,29 329 -685,4...-664,1 29, 43ref 9

115,20 N /17,86 417 -305,2...-192,0 442, 44, 282, 45, 322, 312, 46, 302

ref 10 128,74 N/ 14,52 439 -252,5...-186,7 442, 302, 45, 46, 312ref 11 138,74 N/ 15,43 423 -298,2...-243,5 432, 322, 45ref 12 219,34 N/ 18,21 427 -331,7...-252,0 342, 47, 35, 48, 45ref 13 226,95 N/ 23,26 435 -350,0...-301,4

4.3 Comparison to borehole data

The picked and geometrically corrected surfaces were transported to AutoDesk environment, where they were displayed with other available data. In Figure 28,Figure 30, and Figure 31 are shown the corrected surfaces, boreholes and other relevant information. The depth match of the reflecting surfaces with borehole observations indicate that selected velocity of 5000 m/s can be assumed to be suitable or almost suitable for the processing. In Table 5 are shown boreholes intersecting the surfaces. The actual velocities deeper in the rock mass are at range 5600-5750 m/s (Enescu et al. 2004), but the approximation used in processing takes into account the lower velocities near surface at 0…150 m depths.

Six different groups of reflectors were deduced.

1. Reflectors ref1 and ref8 are dipping gently to the southeast (134-147/8-16), and are located at 600-700 m depth level. Their corresponding structure category is HZ21. Reflectors found 30-50 m above the indications.

2. Almost similarly oriented ref6, intersecting KR29 (485 m), and located 50-100 m above ref1-ref8 or HZ21 (may form a part of it) at depth level 420-500 m

3. Reflectors ref3, ref5, ref9, ref10 and ref11 form a group showing slightly discontinuous character and varying orientations 128 -140/11-19 in different locations, and forming upper (ref3, ref10, ref11) and lower surface (ref5, ref9). Corresponding structures are HZ20A or BFZ098 and HZ20B.

4. Almost similarly oriented ref7 (89/11) at 150-200 m depth levels near KR29, as projected would be some 40 m above the level of HZ20A, and may indicate displacement in the level of corresponding structures.

5. Ref12 and ref13, dipping gently to the SW, and met in slightly deviating two parts in KR22, KR23, KR25 and KR28 at depth levels 320 – 460 m, at 30 m

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vertical distance. Weaker anomalies in boreholes, or may be mixed with other indications.

6. Ref2 dipping steeply to the west 275/64, met at 150 m in KR25, and projected from different distances to intersect at 345 – 517 m borehole lengths in KR4, KR24, KR28 and KR38. No clear borehole indication. May be difficult to project at correct location due to steep orientation.

Table 5. Corrected surfaces and intersecting boreholes.

Surface Intersecting

or

projected

boreholes

Length of

true or

projected

intersection

(m)

Closest

distance (m)

Other projected

lengths (m) from

greater distance

(planarity

considered)

Borehole confirm

ref 1 KR4 705 180 KR7 661, KR29 684 ref 8 KR4

KR7KR29

697 686 709

228 258 199

Near match in KR4 (760) and KR7 (690), clearly above zone in KR29.

ref 6 KR29 485 intersecting KR4 641, KR7 517 No particular indications in boreholes

ref 2 KR25 150 107 KR4 516, KR24 346, KR28 423, KR38 389

Steep zone may be difficult to match. KR4 and KR38 anomaly zones.

ref 3 KR22 KR25 KR28

370 323 367

7250107

KR4 292, KR7 215, KR23 413, KR24 319, KR29 285, KR38 309

10-20 m above distinct anomalies in all boreholes

ref 5 KR4 KR24 KR38

313 325 319

989286

KR7 267, KR22 386, KR23 410, KR25 342, KR28 386, KR29 298

at distinct anomaly locations in all boreholes

ref 7 KR29 185 80 KR4 242, KR7 195, KR22 324, KR23 325, KR24 244, KR25 284, KR28 312, KR38 241

Reflector indication above anomalies in boreholes.

ref 9 KR4 KR7KR29 KR38

348 268 288 359

884186 150

KR22 445, KR24 368, KR25 409, KR28 433

at or near anomaly locations in all boreholes

ref 10 KR4 KR7

291 228

130 intersecting

KR22 369, KR24 307, KR25 326, KR28 326, KR29 266, KR38 300

slightly above or at anomaly locations in all boreholes

ref 11 KR4 KR24 KR28 KR38

292 311 364 303

16 30738

KR7 299, KR22 364, KR25 319, KR29 283

slightly above or at distinct anomaly locations in all boreholes

ref 12 KR22 KR25 KR28

414 350 456

28intersecting 91

KR4 401, KR7 429, KR24 409, KR29 547, KR38 407

ref 13 KR22 KR23 KR25 KR28

380 442 325 443

20485093

KR4 397, KR7 443, KR24 404, KR29 593, KR38 404

Small anomalies, alteration, fracturing in boreholes. May become mixed with other intersections.

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In Figure 28 are shown the picked surfaces and boreholes with bedrock features, e.g. brittle fracture zones (BFZ, Paulamäki et al. 2006), or hydraulically conductive features (HZ, Ahokas & Vaittinen 2007) and different lithological units. Reflections match better to the fractured section locations than the rock type variation.

From the intersections of for example borehole KR07 and two blue surfaces ref9 and ref10, can be seen that the surfaces match with these features in the geological model (Paulamäki et al. 2006). These fit well with borehole observations in KR4, KR7, KR24 and KR38 when projected along the plane. Also reflector intersection at borehole KR25 (ref 12) gets some support from the borehole data (Julkunen et al. 2004).

In Figure 29 is shown a vertical section along the borehole KR07. Red intersection lines of ref9 and ref10 match well with HZ20A and fairly with HZ20B and their borehole intersection depths (Ahokas & Vaittinen 2007).

Figure 28. 3D view (from the south-west) of interpreted surfaces, boreholes (KR), bedrock features and lithological units intersected in boreholes. ONKALO is shown in yellow.

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Figure 29. Section along the KR07.

In Figure 30 are shown the features HZ20A (green) and HZ21 (violet) (Ahokas & Vaittinen 2007 in prep.) and in Figure 31 the brittle fracture zone OL-BFZ098 (turquoise) of geological model (Paulamäki et al. 2006). Surfaces ref10 and ref11 match well with the upper layer (HZ20A) and surface ref1 with the lower layer (HZ21) in Figure 30 (Ahokas & Vaittinen 2007). Ref 9 in Figure 31 matches with the OL-BFZ098, and may indicate it could continue towards borehole KR29 (280 – 330 m, met at 330-331 m). Surface ref5 is located near the borehole KR29 and could be combined with the surface ref9 and therefore also be part of the OL-BFZ098.

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Figure 30. 3D view (from the south-west) of interpreted surfaces, boreholes (KR), HZ20A (green) and HZ21 (violet) and ONKALO (yellow).

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Figure 31. 3D view (from the south-west) of interpreted surfaces, boreholes (KR), OL-BFZ098 (turquoise) and ONKALO (yellow).

In Figure 32 the picked surfaces are shown with the results of 3D survey (Juhlin & Cosma 2006) on stacked sections (same processing phase). The reflection amplitude maxima are seen on the same arrival times in both sections. The 3D survey suggests that many of these reflectors seen in 2D lines, are discontinuous in character over longer distances.

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Figure 32. Matching events in the stacked 2D (Line S46, see APPENDIX 1) and 3D sections (for 3D before dip moveout and migration, Juhlin & Cosma 2006). View to the Southeast.

Evidently the reflecting surfaces correspond to geological structures, e.g., brittle fault zones met at the borehole intersections. These can be confirmed e.g. from KR4, KR7, KR25 and KR29 at borehole depths shown in Table 5 above. The discontinuities on the surfaces suggest slight vertical displacements (faults), though the large scale continuity of the surfaces on the same depth level can be confirmed.

According to location, ref9 (dark blue in Figures 28 - 32) can be met in KR4, and may continue on slightly different level to borehole KR29, matching with BFZ098 with slight vertical offset (330 m). The ref10 (light blue in Figures 28 – 32) is met upper in the borehole KR7 and would match well HZ20A. The ref1 (red) is fitting well with HZ21. There is no direct borehole control for the reflector nearby, but evidently the strongly fractured section in KR4 and KR7 would match this feature. It is not seen continuously in 2D line sections due to low S/N, but in 3D the event is clear and continuous.

In Figure 33 is shown line number S46 and boreholes KR4 and KR7 with P-wave velocity and density logging results. The velocity minima in logging match with the reflectors marked with red arrows. The reflectors ref3, ref5, ref9, ref10 and ref11 seem to correlate to this feature, being slightly offset (or faulted) in different parts, and showing slightly varying orientations 128 -140/11-19 in different locations. Projected intersection point is in KR4 290 m and in KR7 230 m, slightly above true position, like at 315-320 m in KR4.

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Figure 33. Line number S46 and boreholes KR4 (on the left) and KR7 with P-wave velocity (blue) and density (green), a view from the North. The reflector at 130 – 150 ms time is clearly seen in the image, and will match also the borehole geophysical velocity minima and fracturing indications (borehole length 220 m in KR7 and 320 m in KR4). Borehole trace is in yellow; please note the boreholes are off-plane.

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5 CONCLUSIONS

Aim of this work was to process two-dimensional refraction seismic data collected from the ONKALO area using reflection seismic processing methods and to locate gently dipping reflectors from the processed survey lines. This was a demanding task because of a small fold, approximately only four. Survey lines S28-S35, S43-S48, S282, S302, S312, S322, S342, S362, S372, S432, S442, S443, S50 measured in 2002 were selected for the seismic processing. After the processing the two dimensional reflectors were picked in OpendTect visualization environment and combined into three-dimensional surfaces. Special attention was given for the detection of faults and discontinuities. The surfaces were transferred to 3D presentation utility and compared to available geological 3D information (Paulamäki et al. 2006).

Processing was done mainly using free seismic data processing package Seismic Unix (SU). The most important processing steps were the refraction statics and deconvolution. Without these steps and careful selections of parameters it was not possible to see any clear reflectors in stacked sections (Figure 20 a) and Figure 21 b)). Same processing parameters were applied to the whole seismic data set but refraction and residual statics needed to be computed separately for each survey line. Residual statics was the most time-consuming processing step.

Result of this work was a set of two-dimensional seismic sections and three-dimensional surfaces picked from these sections presented in 3D presentation utility. Quality of the seismic data was quite good down to the 200 ms (400 m) but after that signal-to-noise ratio decreases, which can be seen in the seismic sections (APPENDIX 1). Therefore reflectors are mainly found from the upper parts of the data. If the shots are located near the geophones, airwave covers most of the data down to 200 ms (400 m). Processing was completed successfully, as clear two-dimensional reflectors were detected from the data. In 3D these reflectors continue from line to line and construct surfaces which can be compared to borehole observations.

Refraction statics were calculated quite roughly using picked first breaks and replacement velocity of 5000 m/s in order to get the best possible coverage of the ONKALO area within the available schedule. In practise the applied procedure led to adequate accuracy of the results. Another option could have been to use for example a method called seismic travel time tomography (ray tracing) to determine static corrections and near-surface velocity variations (Bergman et al. 2004).

Fold was quite small, which has an effect on stacked sections. With a bigger fold reflectors would have been clearer and have a bigger amplitude, which would have made the interpretation easier. From the stacked sections (Figure 21 a) and Figure 24)we can see that reflectors are mainly seen because of their phase coherence.

Dips and locations of three-dimensional surfaces were corrected using the procedure which corresponds roughly a 3D migration (Prissang et al. 2004). Migrated three-dimensional surfaces were transported to AutoDesk environment, where they were displayed with other data. Depth of the reflectors was determined using the approximate velocity of 5000 m/s. Selecting the velocity e.g. either 5000 m/s, or 5500 m/s, will lead to approx. 10% error in the depth axis.

Because of an airwave, that covers most of the reflectors in the upper parts of the inline shots, one option would have been to remove all the traces with offsets bigger than

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some specified limiting value. This could have reduced noise and made the reflectors clearer, but on the other hand decreased fold. Effective survey would apply longer offsets to cover steeper reflector surfaces, and more fold in stacking.

Processing and interpretation succeeded well because clear two-dimensional reflectors were seen in processed data and corrected three-dimensional surfaces matched well with other data. Quality of the measured data was reasonably good. The obtained high frequencies allowed good resolution of observations. Depth accuracy of converted reflector events is of order of 10% of depth. According to results processing was worthwhile to perform and results were got from the existing data with only the processing costs. Picked surfaces matched well with the borehole control data and 3D survey results. Great advantage was to get information from the ONKALO site where extensive surface seismic surveys may not be possible to perform any more.

The line coverage 100 x 100 m seemed to be sparse to decide on same features on parallel lines. The crossline control of reflectors allowed detection of several 3D surfaces, which are limited in the area. More precise mapping of the subsurface features would require not only higher fold and offset in survey setup, but also denser line coverage, which demands will practically lead to a need for 3D reflection array.

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REFERENCES

Ahokas, H. & Vaittinen, T. 2007. Hydrological model 2006. Under preparation.

Bergman, B., Tryggvason, A. & Juhlin, C. 2004. High-resolution seismic traveltime tomography incorporating static corrections applied to a till-covered bedrock environment. Geophysics, 69, pp 1082-1090.

Enescu, N. , Cosma, C. & Balu, L. 2004. reflection seismics using boreholes at Olkiluoto in 2003 – from investigation design to result validation. Volume 1. Working report 2004-62, 167 p.

Ihalainen, M. 2003. Seismiset refraktioluotaukset Eurajoen Olkiluodossa vuonna 2002. Olkiluoto: Posiva Oy. 97 p. Työraportti 2003-12.

Interpex Limited, http://www.interpex.com, 30.10. 2006. Shareware.

Juhlin, C., Palm, H. & Bergman, B. 2001. Reflection seismic imaging of the upper crystalline crust for characterization of potential repository sites: Fine tuning the seismic source. SKB Technical Report TR-01-31, 49 p.

Juhlin, C., Palm, H. & Bergman, B. 2004. Reflection seismic studies performed in the Laxemar area during 2004. Oskarshamn site investigation. SKB, Stockholm. Report P-04-215, 53 p.

Juhlin, C. & Cosma, C. 2006. A 3D seismic pilot study at Olkiluoto, Finland. Acquisition and Processing. Posiva Working report, in preparation.

Julkunen, A., Kallio, L. & Hassinen, P. 2004. Geophysical borehole logging in boreholes KR23, KR23B, KR24, KR25 and KR25B at Olkiluoto, Eurajoki in 2003. Posiva Working Report 2004-17. 67 p.

Lahti, M. & Heikkinen. E. 2005. Geophysical borehole logging of the boreholes KR23 extension, KR29 and KR29b at Olkiluoto 2004. Posiva Working Report 2005-17, 77 p.

Lehtimäki, T. 2003. Supplementary Interpretation of Seismic Refraction Data at Olkiluoto. Olkiluoto: Posiva Oy. 42 p. Working Report 2003-63.

Li, Xinxiang. 1999. Residual statics analysis using prestack equivalent offset migration. Calgary, Alberta. 141 p. Thesis.

OpendTect, 2006 http://www2.opendtect.org/, 7.11.2006. Open Source Seismic Interpretation System.

Paulamäki, S., Paananen, M., Gehör, S., Kärki, A., Front, K., Aaltonen, I., Ahokas, T., Kemppainen, K., Mattila, J. & Wikström, L., 2006. Geological model of the Olkiluoto Site. Version 0. Posiva Working report 2006-37, 355 p.

Prissang, R., Hellä, P., Lehtimäki, T., Saksa, P., Nummela, J. & Vuento, A. 2004. Identification of mineable blocks in dimension stone rock masses. In Hardygóra, M., Paszkowska, G. & Sikora, M. (eds): Mine Planning and Equipment Selection 2004. Taylor & Francis Group, London, Great Britain. p. 69-74. ISBN 04 1535 937 6

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ReflexW, User’s Manual, Version 3.0, K.J Sandmeier, Zipser Straße 1, D-76227 Karlsruhe, Germany. 345 p.

Saksa, P., Lehtimäki, E. & Heikkinen, E. 2006. Surface 3D reflection seismics – Implementation at the Olkiluoto site. Posiva Working Report , in preparation.

Stockwell, J. Jr. & Cohen, J. 2002. The New SU User’s Manual. 141 p. http://www.seismo.unr.edu/

Vaittinen, T., Ahokas, H., Heikkinen, E., Hellä, P., Nummela, J., Saksa, P., Tammisto, E., Paulamäki, S., Paananen, M., Front, K. & Kärki, A. 2003. Bedrock model of the Olkiluoto site, version 2003/1. Posiva Working Report 2003-43, 266 p.

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APPENDIX 1. STACKED SEISMIC SECTIONS AND PICKED REFLECTORS.

Figure 1. Stacked section from the line S28.

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Figure 2. Reflectors from the line S28.

ref 7

ref 5

ref 6

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Figure 3. Stacked section from the line S282.

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Figure 4. Reflectors from the line S282.

ref 9

Single 1 Single 2

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Figure 5. Stacked section from the line S29.

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Figure 6. Reflectors from the line S29.

ref 7

ref 9

ref 6

ref 8

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Figure 7. Stacked section from the line S30.

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Figure 8. Reflectors from the line S30.

ref 6

ref 5

Single 3

Single 4 Single 5

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Figure 9. Stacked section from the line S302.

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Figure 10. Reflectors from the line S302.

ref 5

ref 10

ref 9

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Figure 11. Stacked section from the line S31.

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Figure 12. Reflectors from the line S31.

ref 5

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Figure 13. Stacked section from the line S312.

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Figure 14. Reflectors from the line S312.

ref 10

ref 9 ref 5

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Figure 15. Stacked section from the line S32.

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Figure 16. Reflectors from the line S32.

ref 5

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Figure 17. Stacked section from the line S322.

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Figure 18. Reflectors from the line S322.

ref 9

ref 11

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Figure 19. Stacked section from the line S33.

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Figure 20. Reflectors from the line S33.

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Figure 21. Stacked section from the line S34.

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Figure 22. Reflectors from the line S34.

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Figure 23. Stacked section from the line S342.

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Figure 24. Reflectors from the line S342.

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Single 6 Single 7

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Figure 25. Stacked section from the line S32.

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Figure 26. Reflectors from the line S35.

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Single 8 Single 9

Single 10Single 11

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Figure 27. Stacked section from the line S32.

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Figure 28. Reflectors from the line S362.

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Single 12

Single 13

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Figure 29. Stacked section from the line S372.

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Figure 30. Reflectors from the line S372.

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Figure 31. Stacked section from the line S43.

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Figure 32. Reflectors from the line S43.

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Single 14

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Figure 33. Stacked section from the line S432.

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Figure 34. Reflectors from the line S432.

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Single 15 Single 16

Single 17

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Figure 35. Stacked section from the line S44.

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Figure 36. Reflectors from the line S44.

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Single 18

Single 19

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Figure 37. Stacked section from the line S442.

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Figure 38. Reflectors from the line S442.

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Figure 39. Stacked section from the line 443.

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Figure 40. Reflectors from the line S443.

Single 20

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Figure 41. Stacked section from the line S45.

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Figure 42. Reflectors from the line S45.

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Figure 43. Stacked section from the line S45.

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Figure 44. Reflectors from the line S46.Vertical reflector indicates possible vertical displacement along a subvertical fault.

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Single 21

Single 22

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Figure 45. Stacked section from the line S47.

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Figure 46. Reflectors from the line S47.

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Single 23

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Figure 47. Stacked section from the line S48.

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Figure 48. Reflectors from the line S48.

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Figure 49. Stacked section from the line S50.

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Figure 50. Reflectors from the line S50.

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