Seismic 2D Reflection Processing and Interpretation of ... - Posiva

Working Report 2006-114Seismic 2D Reflection Processing andInterpretation of Shallow Refraction DataIda ÖhmanEero HeikkinenTomas LehtimäkiDecember 2006POSIVA OYFI-27160 OLKILUOTO, FINLANDTel +358-2-8372 31Fax +358-2-8372 3709

Working Report 2006-114Seismic 2D Reflection Processing andInterpretation of Shallow Refraction DataIda ÖhmanEero HeikkinenTomas LehtimäkiPöyry Environment OyDecember 2006Working Reports contain information on work in progressor pending completion.The conclusions and viewpoints presented in the reportare those of author(s) and do not necessarilycoincide with those of Posiva.

Seismic 2D Reflection Processing and Interpretation ofShallow Refraction DataABSTRACTPosiva Oy takes care of the final disposal of spent nuclear fuel in Finland. In year 2001Olkiluoto was selected for the site of final disposal. Currently construction of theunderground research facility, ONKALO, is going on at the Olkiluoto site.The aim of this work was to use two-dimensional reflection seismic processing methodsto refraction seismic data collected from the ONKALO area in year 2002, and to locategently dipping reflectors from the stacked sections.Processing was done using mainly open source software Seismic Unix. After theprocessing, the most distinct two-dimensional reflectors were picked from seismicsections using visualization environment OpendTect. After picking the features fromcrossing lines were combined into three-dimensional surfaces. Special attention wasgiven for the detection of possible faults and discontinuities. The surfaces were givencoordinates and their orientation was adjusted using a geometric procedure, whichcorresponds roughly a 3D migration, transferred to 3D presentation utility andcompared to available geological information.The advantage of this work is to be able to get three-dimensional reflection seismicresults from existing data set at only processing costs. Survey lines are also partlylocated in ONKALO area where extensive surface seismic surveys may not be possibleto perform.The applied processing method was successful in detecting the reflectors. Mostsignificant steps were the refraction and residual statics, and deconvolution. Somedistinct reflectors can be seen at times 20-200 ms (vertical depths 50...500 m). Thesignal gets noisier below 200 ms. Reflectors are best visible as coherent phase betweenthe adjacent traces, but do not raise much above the surrounding noise level. Higheramount of traces to be stacked would emphasis the reflections and their continuitymore.Reflectors picked on crossing lines match well to borehole observations (KR4, KR7,KR24 and KR38) of fracture zones, and get support from geological and hydrologicalmodels of the site. The observed reflections coincide with fracturing intensity and P-wave velocity minima from boreholes. Reflections coincide also rather well to theseparate 3D seismic results from overlapping area.The results demonstrate that seismic measurements intended for refraction interpretationcan also be successfully processed using reflection seismic processing methods.Increasing number of active geophones and shots, and line density, would enhancereliability of the reflections.Keywords: Seismic, reflection, refraction, processing, interpretation, crystalline,bedrock, migmatite, fracture zone, spent nuclear fuel, geological disposal

Seismisen refraktiomittauksen 2D reflektioprosessointi ja tulkintaTIIVISTELMÄPosiva Oy vastaa radioaktiivisen ydinjätteen loppusijoituksesta Suomessa. Vuonna 2001Olkiluoto valittiin ydinjätteiden loppusijoituspaikaksi. Parhaillaan Olkiluotoon rakennetaanONKALOA, maanalaista tutkimustilaa.Tämän työn tarkoituksena on prosessoida ONKALO-alueelta vuonna 2002 kerättyärefraktioseismistä dataa käyttäen heijastusseismiikkaa varten kehitettyjä prosessointimenetelmiä,sekä tulkita pinotuista sektioista loivakaateisia heijastajia.Prosessointi suoritettiin käyttäen pääasiassa vapaan lähdekoodin ohjelmaa SeismicUnix. Prosessoinnin jälkeen selvimmin erottuvat kaksiulotteiset heijastajat poimittiinseismisistä vertikaalileikkauksista OpendTect-ohjelmalla. Poiminnan jälkeen risteävienlinjojen heijastuspiirteitä yhdistettiin kolmiulotteisiksi pinnoiksi. Poiminnassa kiinnitettiinerityisesti huomiota mahdollisiin siirroksiin ja epäjatkuvuuksiin. Pinnoillelaskettiin koordinaatit ja tehtiin asentokorjaus käyttäen menetelmää, joka vastaa karkeasti3D-migraatiota (Paulamäki et al. 2006). Migratoidut pinnat siirrettiin ohjelmaan,jossa ne voitiin esittää kolmiulotteisesti, ja niitä verrattiin olemassa olevaan geologiseeninformaatioon.Työn etuna on se, että heijastusseismisiä 3D-tuloksia saadaan olemassa olevastarefraktiodatasta pelkin prosessointikustannuksin. Mittauslinjat sijaitsevat osittain alueella,jolla laajoja seismisiä mittauksia ei enää ole mahdollista suorittaa, joten jo olemassaolevan datan hyödyntäminen on tärkeää.Käytetyllä prosessointimenetelmällä onnistuttiin tulkitsemaan heijastajat. Tärkeimmättyövaiheet olivat refraktio- ja residuaalinen staattinen korjaus sekä dekonvoluutio. Joitakinselviä heijastuksia nähdään 20 – 200 ms aikavälillä (50 – 500 m vertikaalisyvyys).Signaalin kohina voimistuu 200 ms jälkeen. Heijastukset havaitaan parhaiten koherentinvaiheen perusteella vierekkäisten kuvaajien välillä, koska amplitudi ei kohoa paljoaympäristön kohinatason yläpuolelle. Suurempi pinoamisen kertaluku vahvistaisi heijastuksiaja niiden jatkuvuutta.Risteäviltä linjoilta poimitut heijastajat osuvat hyvin yhteen kairanreikähavaintojen(KR4, KR7, KR24 ja KR38) rikkonaisuusvyöhykkeiden kanssa, ja saavat tukeageologisista ja hydrologisista malleista. Heijastukset korreloivat kasvaneen, rei’istähavaitun rakotiheyden ja seismisen P-aallon minimien kanssa. Samoin yhteensopivuuson hyvä erillisten 3D-heijastustulosten kanssa päällekkäiseltä alueelta.Tulokset osoittavat että refraktiotulkintaa varten tehtävä seisminen mittaus kannattaasuunnitella siten, että myös reflektioprosessointi on mahdollinen. Lisäämällä aktiivistengeofonien ja lähdepisteiden määrää sekä linjatiheyttä heijastukset nähdään luotettavammin.Avainsanat: Seisminen, heijastus, taittuminen, käsittely, tulkinta, kiteinen peruskallio,migmatiitti, rikkonaisuusvyöhyke, käytetty ydinpolttoaine, geologinen loppusijoitus

1TABLE OF CONTENTSABSTRACTTIIVISTELMÄ1 INTRODUCTION .............................................................................................. 32 SOURCE DATA ................................................................................................ 52.1 Surface seismic data............................................................................. 52.2 Background information ........................................................................ 83 DATA PROCESSING ....................................................................................... 94 INTERPRETATION......................................................................................... 294.1 Two dimensional reflectors ................................................................. 294.2 Three dimensional surfaces ................................................................ 304.3 Comparison to borehole data.............................................................. 335 CONCLUSIONS.............................................................................................. 41REFERENCES ........................................................................................................... 43APPENDIX 1. STACKED SEISMIC SECTIONS AND PICKED REFLECTORS. ....... 45

31 INTRODUCTIONPosiva Oy takes care of the final disposal of spent nuclear fuel in Finland. In year 2001Olkiluoto was selected for the site of final disposal. Currently construction of anunderground research facility, ONKALO, is going on at the Olkiluoto site. SuomenMalmi Oy has carried out shallow refraction seismic surveys in 2001 and 2002 in orderto determine the overburden thickness and to study seismic P-velocity on bedrocksurface and to locate e.g. possible fracture zones (Ihalainen 2003). In year 2001 surveylines from S1 to S27 were measured (15,4 km in total) and in year 2002 survey linesfrom S27 to S69 (17,57 km in total).The aim of this work was to use two-dimensional reflection seismic processingmethods to refraction seismic data collected from the ONKALO area, and to locategently dipping reflectors from the processed survey lines.Processing applied open source software Seismic Unix (SU) (Stockwell & Cohen2002). Processing included reading and re-arranging the data set, removal of noisytraces, geometric spreading correction, bandpass filtering, refraction and residualstatics, deconvolution, airwave muting, automatic gain control, normal moveout andstacking. The goal was to find the best possible processing parameters for the seismicdata set. The refraction measurement array is not optimized for reflection processingwhich leads to quite small 2D fold, approximately only 4, which makes the processinga demanding task.After the processing two-dimensional reflectors will be picked in 3D visualizationenvironment and combined into three-dimensional surfaces. Special attention will begiven for the detection of possible faults and discontinuities.The advantage of this work is to be able to get three-dimensional reflection seismicresults from existing data set at only processing costs. Survey lines are also partlylocated in ONKALO site where extensive surface seismic surveys may not be possibleto 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 wascarried out by Ms. Ida Öhman of Pöyry Environment. Techniques were discussedthrough with and advised by Dr. Christopher Juhlin of Uppsala University, Dr. CalinCosma and Mr. Mircea Cozma of Vibrometric and Mr. Tomas Lehtimäki and Mr. EeroHeikkinen of Pöyry Environment. Mr. Lehtimäki organised the raw data and computedthe geometric conversion of picked surfaces. Mr. Jorma Nummela of PöyryEnvironment converted the surfaces into AutoDesk and Surpac Vision 3D visualisationsoftware.

52 SOURCE DATA2.1 Surface seismic dataOriginal refraction seismic data was collected from Olkiluoto during the summer andautumn 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 velocitiesin the bedrock surface, using refraction intercept time and generalised reciprocal(GRM) interpretation techniques on 2D lines. The interpretations were furtherexamined and merged onto maps of soil thickness and velocity (Lehtimäki 2003).Table 1 displays the information about the survey lines selected for the seismicprocessing. 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 forthe seismic processing were selected to get the best possible coverage of the ONKALOarea 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 distancebetween these points.Line name Northing start Easting start Northing end Easting end Length m28 6791770 1525650 6792010 1525650 240282 6791995 1525650 6792230 1525650 23529 6791727,5 1525700,00 6791980 1525700 252,530 6791800 1525750 6791950 1525750 150302 6791920 1525750 6792250 1525750 33031 6791770 1525800 6791920 1525800 150312 6791900 1525800 6792230 1525800 33032 6791740 1525850 6791890 1525850 150322 6791890 1525850 6792232,5 1525850 342,533 6791830 1525950 6792250 1525950 42034 6791795 1526050 6792137,5 1526050 342,5342 6792047,75 1526050 6792230 1526050 182,2535 6791805 1526150 6792292,5 1526150 487,5362 6791960 1526250 6792192,5 1526250 232,5372 6792030 1526300 6792170 1526300 14043 6791950 1525490 6791950 1525730 240432 6791950 1525720 6791950 1526230 51044 6792000 1525500 6792000 1525650 150442 6792000 1525655 6792000 1525790 135443 6792000 1526130 6792000 1526280 15045 6792050 1525547,5 6792050 1526330 782,546 6792100 1525480 6792100 1525900 42047 6792150 1525340 6792150 1526390 105048 6792250 1526030 6792250 1526170 14050 6792381,32 1526028,9 6792146,76 1526261,02 234,56

6Figure 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 geophonespacing was 5 meters but at the both ends and in the middle of an array it wassupplemented to 2,5 meters.Dynamite (35%) charges of 15-120 g were used as seismic source. The number ofshots for each array was nine, of which four were in-line offset shots 30-120 metersoutside the array and the rest at the both ends and in the middle of an array. Distancesbetween the shotpoints varied from 20 to 30 meters.Line number 342 was surveyed using one meter geophone spacing and elevenshotpoints on each 24 m long array.Recording was done using type 10B, 4,5 MHz vertical geophones with 374 Ohm reelmanufactured by Mark Product’s (Houston, USA) (Ihalainen 2003). Acquisition wascarried 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 thereferences Ihalainen (2003).

7Figure 2. Survey array. At the line 342 geophone spacing was 1 meter and the numberof shots 11.Seismic data was recorded to 409,6 ms (Figure 3 and Figure 4). Quality of the stackeddata is quite good down to 200 ms but after that it gets noisier. Quality of the data alsovaries substantially from line to line as can be seen from Figure 3 and Figure 4. Forexample lines S33 and S34 are located over a rocky outcrop and due to that the data isquite noisy and therefore harder to process with uniform work flow settings. As can beseen in Figure 3, in good data for example first arrivals (P-wave), S-wave and airwaveare easily detected. In the case of a noisy data (Figure 4) this is a lot harder.PShot 1 Shot 2 Shot 3SShot 4AirwaveFigure 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 theline 30. AGC has been performed. Trace number on X-axis and two way travel time inseconds on Y-axis.

8Shot 1 Shot 2 Shot 3 Shot 4SPAirwaveFigure 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-axisand two way travel time in seconds on Y-axis.2.2 Background informationThe processed and interpreted seismic results were compared and validated to set ofexisting knowledge on the site.The seismic velocities and signal frequency range have been investigated in precedingseismic VSP works (Enescu et al. 2004). Distribution of velocity data and velocityanomaly locations in boreholes have been extracted from borehole geophysicallogging, e.g. Julkunen et al. (2004), Lahti & Heikkinen (2005). Petrophysicalproperties of Olkiluoto lithology, and the elastic contrasts, were considered duringprior modelling by Mr. Tomas Lehtimäki (Saksa 2006, in preparation) for geometricalobservability, frequency range and attenuation; and by Dr. Christopher Juhlin inUppsala for considerations of, e.g., stacking fold and signal to noise ratio.Geometrical information on potentially reflecting bedrock features have been reviewedfrom bedrock model descriptions. These include features interpreted on basis ofhydrological model data (Ahokas & Vaittinen 2007), geological observations(Paulamäki et al. 2006), and interpretations based on multidisciplinary bedrockproperty classifications (Vaittinen et al. 2003). Results can be also directly comparedand reviewed against VSP and 3D seismic interpretations on the site (Enescu et al.2004, Juhlin & Cosma 2006).

93 DATA PROCESSINGThe aim was to perform reflection seismic processing for two-dimensional seismiclines, surveyed originally for refraction seismic interpretation. Advantage of this workis to get three-dimensional reflection seismic results from the existing data at onlyprocessing costs. Processing was based on a processing flow of SKB studies presentedin Juhlin et al. (2001, 2004) and testing of processing to data set of this report for lineS28, 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 locatepossible subvertical faults.Before seismic interpretation the survey data must be carefully processed. Theprocessing steps are presented in Table 2. Line S28 is used here to exemplify theprocessing steps (see processing flow in Table 2). Practically no reflectors can be seenin 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 thoughautomatic gain control (AGC) is applied to data at the end of processing, it has beenapplied to images in order to make the visualization more illustrative. AGC improvesvisibility of late-arriving events in which attenuation or wavefront divergence hascaused amplitude decay.The most important processing steps to bring the reflections visible were refractionstatics and deconvolution. The goal was to find the processing parameters that could beeasily 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 andweathered layers. Deconvolution will sharpen the signal signature and remove multiplewaves from reflections. During deconvolution, adding noise serves also as frequencyequalization (spectral whitening).

10Figure 5. Raw shot gather from the line S28 with automatic gain control. First nineshots on line. Trace number on X-axis and two way travel time in seconds on Y-axis.Table 2. Processing flow and parameters.Processing stepParameters1. Convert SEG2 data into SEGY (Figure 5)2. Remove noisy traces3. Set geometry4. Geometric spreading correction 1,5Multiply by t5. Bandpass filter (Figure 8) 30-60-400-600 Hz6. Refraction statics (Figure 11)7. Set CDP numbers8. Deconvolution (Figure 12) Minlag: 0,01msMaxlag: 40 msStart of autocorrelation: 0 offset: 100 ms; maxoffset: 120 sEnd of autocorrelation: 0 offset: 300 ms; maxoffset: 400 msNoise: 1 %9. Bandpass filter 0-100 ms: 70-140-300-450 Hz50-200 ms: 60-120-300-450 Hz150-500 ms: 50-100-270-400 Hz10. Mute (Figure 14) Linear velocity: 340 m/sWidth: 0 offset: 10 ms; max offset: 15 msTaper before hard mute: 1000 samples11. Automatic Gain Control (AGC) Window: 50 ms12. Residual statics (Figure 16)13. Normal Moveout (NMO) (Figure 17) Velocity: 5000 m/sStretch mute: 4Number of points to taper: 100014. Stack (Figure 21 a) )

11Processing was performed using free seismic data processing package Seismic Unix(SU) (Stockwell & Cohen 2002). Refraction seismic data SEG-2 format was convertedinto SEG-Y format before importing into SU (Table 2, item 1), using sharewaresoftware IXseg2segy (Interpex Ltd). Number of samples in SEG-2 format was limited,and conversion was preferred rather than down sampling. In down sampling somefeatures 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 locatednear 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, item3). 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, shotnumber, geophone number, shot position, geophone position, common depth point(CDP) position and offset must be set. Common depth point is a common reflectingpoint at depth on a reflector (see Figure 6). In the case of planar layers, CDP is ahalfway point between a source and a receiver as illustrated in Figure 6. In this workthe CDP locations have been computed assuming that reflectors are planar. Geometrywas read from the ASCII file, which was created with Microsoft Excel, and applied todata using Seismic Unix. Example of geometry file is shown inFigure 6. Definition of a common depth point in the case of a planar reflector.

12Table 3. Example of a geometry file from the line 28. First 12 traces.TracenumberShotnumberGeophonenumberShotposition mGeophoneposition mCDPposition mOffset m1 1 1 -60 0 -30 602 1 2 -60 2,5 -28,75 62,53 1 3 -60 5 -27,5 654 1 4 -60 7,5 -26,25 67,55 1 5 -60 12,5 -23,75 72,56 1 6 -60 17,5 -21,25 77,57 1 7 -60 22,5 -18,75 82,58 1 8 -60 27,5 -16,25 87,59 1 9 -60 32,5 -13,75 92,510 1 10 -60 37,5 -11,25 97,511 1 11 -60 42,5 -8,75 102,512 1 12 -60 45 -7,5 105Geometric spreading correction (Table 2, item 4) was applied to seismic data by1,5multiplying amplitude data by t . Selection of parameter was based on a testing andreferences (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 followingparameters.lower cutoff frequency: 30 Hzlower plateau frequency: 60 Hzupper plateau frequency: 400 Hzupper cutoff frequency: 600 HzPurpose of this preliminary filtering was to remove the highest and the lowestfrequencies. Selection of parameters was based on a raw spectrum. Example of aspectrum from the line S28 is shown in Figure 7. The frequency varies from very lowto very high frequencies. Shot gather after the preliminary filtering is shown in Figure8. Reflectors are not yet visible.

13Figure 7. Original spectrum from the line S28. Traces 297-363. Selection ofparameters for preliminary filtering was based on this spectrum in order to remove thehighest and lowest frequencies.

14Figure 8. Shot gather from the line S28 after the preliminary filtering with automaticgain control. First nine shots. Trace number on X-axis and two way travel time inseconds on Y-axis.Refraction static corrections (Table 2, item 6) were calculated using Microsoft Exceland were applied to data after the preliminary filtering. Values of static correctionsmust be integers in milliseconds. The purpose of the refraction static corrections was toeliminate the effect of the weathering layer and the surface elevation variations (seeFigure 9). Refraction statics calculation was based on a first P-wave direct arrivaltimes (first breaks, see Figure 3). Refracted first breaks represent the base of aweathering layer.SHOTRECEIVERSURFACEWEATHERING LAYERv = 5000 m/sFigure 9. Refraction static corrections eliminate the effect of the weathering layer andthe surface elevation variations. Arrows represent the value of correction applied totrace located between the shot and the receiver.The static error was removed from each trace by computing the theoretical first breaksusing the replacement velocity of 5000 m/s and trace offset. Correction was obtainedby subtracting theoretical first break from observed first break. After applyingrefraction static corrections to seismic data, the base of weathering layer becomes a

15new datum and elevation differences between the shot and the geophone and betweenthe geophones are eliminated (Figure 9). Because depth of the real weathering layermay 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 previousinterpretations (Ihalainen 2003, Lehtimäki 2003), which leads to +/- 0,8 ms error intwo 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 errorand 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 lowvelocity volumes near surface. These may be defined using ray-tracing inversion offirst 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 theapproach is easy and fast and therefore adequate and reasonable to perform. Exampleof a shot gather before and after the refraction statics is shown in Figure 10 andFigure 11.Figure 10. First three shots with AGC from the line S28 after the preliminary filteringbut without refraction statics. Trace number on X-axis and two way travel time inseconds on Y-axis.

16Figure 11. First three shots with AGC from the line S28 after the preliminary filteringand refraction statics. Trace number on X-axis and two way travel time in seconds onY-axis.Deconvolution (Table 2, item 8) applied Wiener predictive error filtering. Aim was torecover high frequencies, attenuate multiples, equalize amplitudes, produce a zerophasewavelet and generally affect the wave shape. Deconvolution was performedusing the following parameters and is one of the most important processing steps.First lag of prediction filter: 0,0001 sOperator length: 0,040 sStart of autocorrelation window: min offset 0,1 s, max offset 0,12 sEnd of autocorrelation window: min offset 0,3 s, max offset 0,4 sNoise: 1 %Stacked sections were compared with and without deconvolution in Figure 21 a) andFigure 21 b), respectively. Figures indicate the effect of deconvolution. After thedeconvolution the data was filtered (Table 2, item 9) with similar filter as beforedeconvolution, using parameters shown below.0-100 mslower cutoff frequency: 70 Hzlower plateau frequency: 140 Hzupper plateau frequency: 300 Hzupper cutoff frequency: 450 Hz

1750-200 mslower cutoff frequency: 60 Hzlower plateau frequency: 120 Hzupper plateau frequency: 300 Hzupper cutoff frequency: 450 Hz150-500 mslower cutoff frequency: 50 Hzlower plateau frequency: 100 Hzupper plateau frequency: 270 Hzupper cutoff frequency: 400 HzShot 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 inthe shot gathers where the shot point is located between the geophones because of theairwave.Figure 12. Shot gather from the line S28 after deconvolution and second filtering withAGC. Reflectors can be seen under 130 ms and 200 ms marked with red and bluearrows respectively. Airwave is marked with orange arrow. Trace number on X-axisand 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 offsetgathers (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

18after 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-arrivingevents 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 ismarked 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 (seeFigure 12). Some residual errors still remain, which must be corrected for. Theseerrors can be seen after deconvolution as displacements in first breaks and the reflectedevents. The residual statics (Table 2, item 12) are plus-minus errors with respect to thelong wavelength trend of travel time anomalies due to the near-surface effects (Li1999). Corrections were applied to traces by picking the first break maxima andcomputing their differences to the theoretical first breaks, which were computed duringthe refraction statics.

19Original first breaks were picked to zero amplitude (crossover). This work appliedmaximum 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 +/- 2m which corresponds to 2 ms shift in two way travel time. In Figure 15 is shown ashot gather and in Figure 20 b) a stacked section before the residual statics and inFigure 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 staticswere not applied to the data from the survey lines S33 and S34 because reliable pickingof 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 online.

20Figure 16. Shot gather from the line S28 after the muting and residual statics. Tracenumber 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 theseparation between seismic sources and receivers and must be performed prior tostacking. NMO velocity used was 5000 m/s and stretch mute 4. Samples with NMOstretch exceeding stretch mute were zeroed. Shot gather after the normal moveout isshown in Figure 17. In Figure 18 is shown a detailed example of the first shot fromthe line S28. Originally first breaks and reflecting events are hyperbolic but NMOstraightens them up.

21Figure 17. Shot gather from the line S28 after the normal moveout. Trace number onX-axis and two way travel time in seconds on Y-axis. First 4 shots.

22Figure 18. First shot from the line S28 before and after NMO. Red line demonstrateshow NMO straightens up first breaks.After NMO data can be stacked (Table 2, item 14). First it must be sorted intocommon depth point gathers, which means that data is sorted by its CDP position, andCDP positions must be changed into CDP numbers. Traces with the same CDP numberare stacked. CDP numbers are integers and calculated based on a position of eachCDP. 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 minimumfold one. Figure 19 demonstrates principle of stacking. In the line 342 geophonespacing was smaller so bin is 1 meter. Each stacked sample is divided by the squareroot of non-zero values stacked. Final stacked section from the line S28 is shown inFigure 21 a). Only the first 300 ms of the data are displayed because of a low signalto-noiseratio in the lower parts of the data.

23a)CDP position b)CDP numberFigure 19. a) Traces before stack b) Same traces after stack. Six traces within 2,5 mbin (red and green lines in figure a) ) are stacked. Corresponding stacked traces aremarked with red and green arrows in figure b). In reality CDP positions are notequally spaced and therefore fold varies.

24a) b)Figure 20. a) Stacked section without refraction and residual statics from the line S28down 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. CDPnumber on X-axis and two way travel time in seconds on Y-axis.

25a) b)Figure 21. a) Final stacked section from the line S28 down to 300 ms using a wiggletrace 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 numberon X-axis and two way travel time in seconds on Y-axis.

26Figure 22. Stacked section without refraction and residual statics from the line S342down to 300 ms. CDP number on X-axis and two way travel time in seconds on Y-axis.

27Figure 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.

28Figure 24. Final stacked section from the line S342 down to 300 ms using a wiggletrace display. CDP number on X-axis and two way travel time in seconds on Y-axis.

294 INTERPRETATIONAfter the seismic processing has been performed for the selected set of refractionseismic survey lines, data was interpreted. First step was to examine two dimensionalstacked sections, which can be found from the APPENDIX 1, and to locate possiblereflectors. After this, two-dimensional stacked sections were imported into thevisualization environment OpendTect (OpendTect 2006) and reflectors were picked in3D.4.1 Two dimensional reflectorsTwo dimensional seismic data from the survey lines shown in Figure 1, was processedusing the processing parameters in Table 2. The result was a set of stacked seismicsections which can bee seen in APPENDIX 1 using variable density display. Thesetwo-dimensional sections can be used to locate the reflectors but the actual picking isdone in 3D. Taking a closer look at the reflector below 130 ms in lines S28, S29, S30and S31, it can be seen continuing from line to line. Very clear reflectors can be seen inseveral lines but for example in line S47 only few weak ones are seen. Reflectors aremostly found from the upper parts of the seismic sections. This is due to the lowersignal-to-noise ratio (see shot gathers, Figure 5) in the later times of the data (greaterdepths). This can also be seen from the stacked sections (see APPENDIX 1). Twodimensionalreflectors are shown in APPENDIX 1.Some reflectors may not appear to be very clear in first place, and may be hard todetect from individual lines. Different image colour settings, aspect ratios and scaleswere 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 and362) the reflectors are marked with red arrows.In APPENDIX 1 scale is 1:5000 in order to display data more clear. Picking was easierwith stretched X dimension in 3D.Depth of the reflectors is determined using the approximate velocity of 5000 m/s. Thevelocities used in static correction and NMO give a generic idea on the real velocitiesin bedrock. However the true velocity has to be confirmed using velocity fitting ondiffractions seen on seismic sections, from external sources (VSP data and 3Dreflection data) and with using a borehole control. Processing has applied a phaseconsistent (zero phase) work flow. Correctness of depth axis will rely on recognition ofcorrect phase of the reflected arrival, e.g. ¼ - ½ wavelength late picks will meanapprox. 5-10 m too deep depth level or the reflection. Selecting the velocity e.g. either5000 m/s, or 5500 m/s, will lead to approx. 10% error in the depth axis.

30Figure 25. Example of a weak reflector continuing from line S48 to line S50 to lineS362. It would be hard to locate the reflector from the single lines without the helpfrom the crossing lines.4.2 Three dimensional surfacesTwo-dimensional stacked sections were imported into OpendTect visualizationenvironment, where reflectors were picked. Sections were displayed using variabledensity display. In an intersection of two lines, reflectors may continue from line toline which allows three dimensional picking. Example of reflectors continuing fromline to line is shown in Figure 26. Reflectors picked from crossing lines, constructsurfaces. After all the relevant surfaces and reflectors were picked, they were mergedinto larger surfaces. Still some single two-dimensional reflectors remain.Example of a three-dimensional surface is shown in Figure 27. This surface consists ofreflectors 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 inAPPENDIX 1. 2D reflectors constructing surfaces are named according to the surfacename and single reflectors with a prefix ‘single’. Surfaces were mainly in focus butalso some single reflectors can be found interesting (see below). Normally the highamplitude reflectors are not continuous over the whole survey area, but display ratherbroken and some times discontinuous character. Also abundant diffracted energy (steep

31events) indicates presence of offsetting or terminating structures. Steep events aremostly seen on ca. 1400-1600 m/s velocities (Stoneley waves), some residuals ofairwave can be seen, too (340 m/s). Some diffracted P or S-waves are also seen onsome locations. F-K filtering at -2000 …0…+2000 m/s window remove these eventsand make the S/N ratio of deeper sections better.Figure 26. Intersection of lines S45 and S322. Reflectors continue from line to line andare marked with arrows.

32Figure 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, werecorrected for offset and offline reflection geometry. The original picks are displayed onthe sections with their apparent dips (see APPENDIX 1). The observations aregeometrically tilted so, that the shortest distance from CDP is measured along thenormal of the reflection plane (reflector is tilted towards the up-dip direction). Thiscorresponds roughly a 3D migration, but is a simplified procedure (Prissang et al.2004). Table 4 shows the information on the corrected surfaces. Surfaces are displayedin Figure 28.In Figure 44 in APPENDIX 1 is shown an interesting breakout and discontinuity of areflecting surfaces ref 9 and ref 10, indicating possible vertical displacement along asubvertical fault. The apparent diffracted velocities near the event match to Stoneleyarrivals.

33Table 4. Positions and dips for migrated three dimensional surfacesSurfacenameDip direction/ Dip(degrees from Northand Horizontal)Two waytravel time(ms)Depth (m)Picked from the linesref 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 9442, 44, 282, 45, 322, 312,46, 302115,20 N /17,86 417 -305,2...-192,0ref 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...-301,44.3 Comparison to borehole dataThe picked and geometrically corrected surfaces were transported to AutoDeskenvironment, where they were displayed with other available data. In Figure 28,Figure 30, and Figure 31 are shown the corrected surfaces, boreholes and otherrelevant information. The depth match of the reflecting surfaces with boreholeobservations indicate that selected velocity of 5000 m/s can be assumed to be suitableor almost suitable for the processing. In Table 5 are shown boreholes intersecting thesurfaces. 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 thelower 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), andare located at 600-700 m depth level. Their corresponding structure category isHZ21. Reflectors found 30-50 m above the indications.2. Almost similarly oriented ref6, intersecting KR29 (485 m), and located 50-100m above ref1-ref8 or HZ21 (may form a part of it) at depth level 420-500 m3. Reflectors ref3, ref5, ref9, ref10 and ref11 form a group showing slightlydiscontinuous character and varying orientations 128 -140/11-19 in differentlocations, 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, asprojected would be some 40 m above the level of HZ20A, and may indicatedisplacement in the level of corresponding structures.5. Ref12 and ref13, dipping gently to the SW, and met in slightly deviating twoparts in KR22, KR23, KR25 and KR28 at depth levels 320 – 460 m, at 30 m

34vertical distance. Weaker anomalies in boreholes, or may be mixed with otherindications.6. Ref2 dipping steeply to the west 275/64, met at 150 m in KR25, and projectedfrom different distances to intersect at 345 – 517 m borehole lengths in KR4,KR24, KR28 and KR38. No clear borehole indication. May be difficult toproject at correct location due to steep orientation.Table 5. Corrected surfaces and intersecting boreholes.SurfaceIntersectingorprojectedboreholesLength oftrue orprojectedintersection(m)Closestdistance (m)Other projectedlengths (m) fromgreater distance(planarityconsidered)ref 1 KR4 705 180 KR7 661, KR29 684ref 8 KR4KR7KR29697686709228258199Borehole confirmNear match in KR4(760) and KR7(690), clearly abovezone in KR29.ref 6 KR29 485 intersecting KR4 641, KR7 517 No particularindications inboreholesref 2 KR25 150 107 KR4 516, KR24 346,KR28 423, KR38 389ref 3ref 5KR22KR25KR28KR4KR2437032336731332572501079892KR4 292, KR7 215,KR23 413, KR24 319,KR29 285, KR38 309KR7 267, KR22 386,KR23 410, KR25 342,KR38 319 86KR28 386, KR29 298ref 7 KR29 185 80 KR4 242, KR7 195,KR22 324, KR23 325,KR24 244, KR25 284,KR28 312, KR38 241ref 9ref 10ref 11ref 12ref 13KR4KR7KR29KR38KR4KR7KR4KR24KR28KR38KR22KR25KR28KR22KR23KR25KR28348268288359291228292311364303414350456380442325443884186150130intersecting163073828intersecting9120485093KR22 445, KR24 368,KR25 409, KR28 433KR22 369, KR24 307,KR25 326, KR28 326,KR29 266, KR38 300KR7 299, KR22 364,KR25 319, KR29 283KR4 401, KR7 429,KR24 409, KR29 547,KR38 407KR4 397, KR7 443,KR24 404, KR29 593,KR38 404Steep zone may bedifficult to match.KR4 and KR38anomaly zones.10-20 m abovedistinct anomaliesin all boreholesat distinct anomalylocations in allboreholesReflector indicationabove anomalies inboreholes.at or near anomalylocations in allboreholesslightly above or atanomaly locationsin all boreholesslightly above or atdistinct anomalylocations in allboreholesSmall anomalies,alteration,fracturing inboreholes. Maybecome mixed withother intersections.

35In Figure 28 are shown the picked surfaces and boreholes with bedrock features, e.g.brittle fracture zones (BFZ, Paulamäki et al. 2006), or hydraulically conductivefeatures (HZ, Ahokas & Vaittinen 2007) and different lithological units. Reflectionsmatch better to the fractured section locations than the rock type variation.From the intersections of for example borehole KR07 and two blue surfaces ref9 andref10, 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, KR24and KR38 when projected along the plane. Also reflector intersection at boreholeKR25 (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 intersectionlines of ref9 and ref10 match well with HZ20A and fairly with HZ20B and theirborehole 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 inyellow.

36Figure 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 ref11match 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 becombined with the surface ref9 and therefore also be part of the OL-BFZ098.

37Figure 30. 3D view (from the south-west) of interpreted surfaces, boreholes (KR),HZ20A (green) and HZ21 (violet) and ONKALO (yellow).

38Figure 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 amplitudemaxima are seen on the same arrival times in both sections. The 3D survey suggeststhat many of these reflectors seen in 2D lines, are discontinuous in character overlonger distances.

39Figure 32. Matching events in the stacked 2D (Line S46, see APPENDIX 1) and 3Dsections (for 3D before dip moveout and migration, Juhlin & Cosma 2006). View to theSoutheast.Evidently the reflecting surfaces correspond to geological structures, e.g., brittle faultzones 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 thesurfaces suggest slight vertical displacements (faults), though the large scale continuityof 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 maycontinue on slightly different level to borehole KR29, matching with BFZ098 withslight vertical offset (330 m). The ref10 (light blue in Figures 28 – 32) is met upper inthe borehole KR7 and would match well HZ20A. The ref1 (red) is fitting well withHZ21. There is no direct borehole control for the reflector nearby, but evidently thestrongly fractured section in KR4 and KR7 would match this feature. It is not seencontinuously in 2D line sections due to low S/N, but in 3D the event is clear andcontinuous.In Figure 33 is shown line number S46 and boreholes KR4 and KR7 with P-wavevelocity and density logging results. The velocity minima in logging match with thereflectors marked with red arrows. The reflectors ref3, ref5, ref9, ref10 and ref11 seemto correlate to this feature, being slightly offset (or faulted) in different parts, andshowing slightly varying orientations 128 -140/11-19 in different locations. Projectedintersection point is in KR4 290 m and in KR7 230 m, slightly above true position, likeat 315-320 m in KR4.

40Figure 33. Line number S46 and boreholes KR4 (on the left) and KR7 with P-wavevelocity (blue) and density (green), a view from the North. The reflector at 130 – 150ms time is clearly seen in the image, and will match also the borehole geophysicalvelocity minima and fracturing indications (borehole length 220 m in KR7 and 320 min KR4). Borehole trace is in yellow; please note the boreholes are off-plane.

415 CONCLUSIONSAim of this work was to process two-dimensional refraction seismic data collectedfrom the ONKALO area using reflection seismic processing methods and to locategently dipping reflectors from the processed survey lines. This was a demanding taskbecause 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 2002were selected for the seismic processing. After the processing the two dimensionalreflectors were picked in OpendTect visualization environment and combined intothree-dimensional surfaces. Special attention was given for the detection of faults anddiscontinuities. The surfaces were transferred to 3D presentation utility and comparedto 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 anddeconvolution. Without these steps and careful selections of parameters it was notpossible 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 refractionand residual statics needed to be computed separately for each survey line. Residualstatics was the most time-consuming processing step.Result of this work was a set of two-dimensional seismic sections and threedimensionalsurfaces 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 thatsignal-to-noise ratio decreases, which can be seen in the seismic sections (APPENDIX1). Therefore reflectors are mainly found from the upper parts of the data. If the shotsare located near the geophones, airwave covers most of the data down to 200 ms (400m). Processing was completed successfully, as clear two-dimensional reflectors weredetected from the data. In 3D these reflectors continue from line to line and constructsurfaces which can be compared to borehole observations.Refraction statics were calculated quite roughly using picked first breaks andreplacement velocity of 5000 m/s in order to get the best possible coverage of theONKALO area within the available schedule. In practise the applied procedure led toadequate accuracy of the results. Another option could have been to use for example amethod called seismic travel time tomography (ray tracing) to determine staticcorrections and near-surface velocity variations (Bergman et al. 2004).Fold was quite small, which has an effect on stacked sections. With a bigger foldreflectors would have been clearer and have a bigger amplitude, which would havemade 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 procedurewhich corresponds roughly a 3D migration (Prissang et al. 2004). Migrated threedimensionalsurfaces were transported to AutoDesk environment, where they weredisplayed with other data. Depth of the reflectors was determined using theapproximate velocity of 5000 m/s. Selecting the velocity e.g. either 5000 m/s, or 5500m/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 inlineshots, one option would have been to remove all the traces with offsets bigger than

42some specified limiting value. This could have reduced noise and made the reflectorsclearer, but on the other hand decreased fold. Effective survey would apply longeroffsets to cover steeper reflector surfaces, and more fold in stacking.Processing and interpretation succeeded well because clear two-dimensional reflectorswere seen in processed data and corrected three-dimensional surfaces matched wellwith other data. Quality of the measured data was reasonably good. The obtained highfrequencies allowed good resolution of observations. Depth accuracy of convertedreflector events is of order of 10% of depth. According to results processing wasworthwhile to perform and results were got from the existing data with only theprocessing costs. Picked surfaces matched well with the borehole control data and 3Dsurvey results. Great advantage was to get information from the ONKALO site whereextensive 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 onparallel lines. The crossline control of reflectors allowed detection of several 3Dsurfaces, which are limited in the area. More precise mapping of the subsurfacefeatures would require not only higher fold and offset in survey setup, but also denserline coverage, which demands will practically lead to a need for 3D reflection array.

43REFERENCESAhokas, H. & Vaittinen, T. 2007. Hydrological model 2006. Under preparation.Bergman, B., Tryggvason, A. & Juhlin, C. 2004. High-resolution seismic traveltimetomography incorporating static corrections applied to a till-covered bedrockenvironment. Geophysics, 69, pp 1082-1090.Enescu, N. , Cosma, C. & Balu, L. 2004. reflection seismics using boreholes atOlkiluoto in 2003 – from investigation design to result validation. Volume 1. Workingreport 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 uppercrystalline crust for characterization of potential repository sites: Fine tuning theseismic source. SKB Technical Report TR-01-31, 49 p.Juhlin, C., Palm, H. & Bergman, B. 2004. Reflection seismic studies performed in theLaxemar 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 inboreholes 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 KR23extension, KR29 and KR29b at Olkiluoto 2004. Posiva Working Report 2005-17, 77 p.Lehtimäki, T. 2003. Supplementary Interpretation of Seismic Refraction Data atOlkiluoto. Olkiluoto: Posiva Oy. 42 p. Working Report 2003-63.Li, Xinxiang. 1999. Residual statics analysis using prestack equivalent offsetmigration. Calgary, Alberta. 141 p. Thesis.OpendTect, 2006 http://www2.opendtect.org/, 7.11.2006. Open Source SeismicInterpretation 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 OlkiluotoSite. 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

44ReflexW, User’s Manual, Version 3.0, K.J Sandmeier, Zipser Straße 1, D-76227Karlsruhe, 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 theOlkiluoto site, version 2003/1. Posiva Working Report 2003-43, 266 p.

45APPENDIX 1. STACKED SEISMIC SECTIONS AND PICKED REFLECTORS.Figure 1. Stacked section from the line S28.

46ref 7ref 5ref 6Figure 2. Reflectors from the line S28.

47Figure 3. Stacked section from the line S282.

48Single 1Single 2ref 9Figure 4. Reflectors from the line S282.

49Figure 5. Stacked section from the line S29.

50ref 7ref 9ref 6ref 8Figure 6. Reflectors from the line S29.

51Figure 7. Stacked section from the line S30.

52Single 3ref 5Single 4Single 5ref 6Figure 8. Reflectors from the line S30.

53Figure 9. Stacked section from the line S302.

54ref 5ref 10ref 9Figure 10. Reflectors from the line S302.

55Figure 11. Stacked section from the line S31.

56ref 5Figure 12. Reflectors from the line S31.

57Figure 13. Stacked section from the line S312.

58ref 5ref 9ref 10Figure 14. Reflectors from the line S312.

59Figure 15. Stacked section from the line S32.

60ref 5Figure 16. Reflectors from the line S32.

61Figure 17. Stacked section from the line S322.

62ref 11ref 9Figure 18. Reflectors from the line S322.

63Figure 19. Stacked section from the line S33.

64ref 13Figure 20. Reflectors from the line S33.

65Figure 21. Stacked section from the line S34.

66ref 13Figure 22. Reflectors from the line S34.

67Figure 23. Stacked section from the line S342.

68Single 7Single 6ref 12ref 3Figure 24. Reflectors from the line S342.

69Figure 25. Stacked section from the line S32.

70ref 12Single 8Single 9Single 10Single 11ref 1Figure 26. Reflectors from the line S35.

71Figure 27. Stacked section from the line S32.

72Single 12Single 13ref 2ref 1Figure 28. Reflectors from the line S362.

73Figure 29. Stacked section from the line S372.

74ref 1Figure 30. Reflectors from the line S372.

75Figure 31. Stacked section from the line S43.

76Single 14ref 5ref 8Figure 32. Reflectors from the line S43.

77Figure 33. Stacked section from the line S432.

78ref 5ref 11Single 15Single 16Single 17Figure 34. Reflectors from the line S432.

79Figure 35. Stacked section from the line S44.

80Single 18ref 9Single 19Figure 36. Reflectors from the line S44.

81Figure 37. Stacked section from the line S442.

82ref 10ref 9Figure 38. Reflectors from the line S442.

83Figure 39. Stacked section from the line 443.

84Single 20Figure 40. Reflectors from the line S443.

Figure 41. Stacked section from the line S45.85

86ref 10ref 10ref 9ref 11ref 12Figure 42. Reflectors from the line S45.

87Figure 43. Stacked section from the line S45.

88ref 10ref 10ref 9Single 22Single 21Figure 44. Reflectors from the line S46.Vertical reflector indicates possible verticaldisplacement along a subvertical fault.

Figure 45. Stacked section from the line S47.89

90ref 9Single 23ref 12ref 3Figure 46. Reflectors from the line S47.

91Figure 47. Stacked section from the line S48.

92ref 12ref 1Figure 48. Reflectors from the line S48.

93Figure 49. Stacked section from the line S50.

94ref 2ref 1Figure 50. Reflectors from the line S50.