ONKALO 3D Tunnel Seismic Investigations, Olkiluoto 2013

ONKALO 3D Tunnel Seismic Investigations,Olkiluoto 2013

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POSIVA OY

Olki luoto

FI-27160 EURAJOKI, F INLAND

Phone (02) 8372 31 (nat. ) , (+358-2-) 8372 31 ( int. )

Fax (02) 8372 3809 (nat. ) , (+358-2-) 8372 3809 ( int. )

October 2014

Working Report 2014-49

Nicoleta Enescu, Cal in Cosma, Jonathan Crawford

October 2014

Working Reports contain information on work in progress

or pending completion.

Nicoleta Enescu, Cal in Cosma, Jonathan Crawford

Vibrometr ic Oy Cosma

Working Report 2014-49

ONKALO 3D Tunnel Seismic Investigations,Olkiluoto 2013

ABSTRACT

POSIVA Oy conducts bedrock investigations at the spent nuclear fuel final disposal site at Olkiluoto, in western Finland. The purpose of these efforts, which include a significant R&D component, is to ensure compliance with the requirements set forth for the long-term safety of final disposal. The excavation of the access tunnel to the repository hosts the ONKALO underground rock characterization facility. The investigations carried out in ONKALO focus on the bedrock and groundwater conditions prevailing on the final disposal site and how construction work affects them. Deformation zones and hydraulically conductive zones can limit the areas which are suitable for a deposition hole to be placed. The main objective of the tunnel seismic investigations presented here is to develop a seismic investigation technique for deposition area characterization. The field work consisted of 3 receiver lines using 3-component geophones and sources locations using the Vibsist-500 for 6 profiles, the Vibsist-20 for 1 profile (sparse), and a mechanical borehole hammer, MH-70, for 5 profiles for a total of 12 profiles. This investigation took place in the ONKALO demonstration area. Design of the seismic field work is based on previous tunnel seismic works in ONKALO (Cosma et al. 2008 and 2011) and pre-survey numerical modeling for field data and processing (Heinonen et al. 2013). The fieldwork was carried out in June 2013. Tomographic inversion of P-wave first arrival times was done on combined data sets, containing data from several shot-receiver configurations along tunnels and boreholes. The velocity distributions derived by tomographic inversion were verified by comparison with the forward modeled profiles. The Image Point (IP) migration method is characterized by is its ability to accumulate reflection events measured in the time distance data sets into points in the IP domain, which permits the enhancement of coherent backscattered events. The result of the 3D IP migration consists of migrated sections oriented to preferred azimuths, around each receiver line. The seismic surveys described here were used to characterize deformation zones and fractures present in the investigated rock mass, which demonstrated the capability of reflection seismics to detect and locate geological features of diverse character and orientations. The use of the 3D IP migration technique was instrumental for the success of this imaging exercise. The last phase of interpretation applied forward modeling of the seismic events, partially by comparing with geological structures. High quality results were obtained, while operating in tunnel working conditions. Numerous reflectors were visible across multiple profiles and several of those could be directly associated with known geological structures. Using the gypsum plaster in the receiver holes allowed for good contact between the geophones and the tunnel wall which increased the quality of the data. Keywords: 3D tunnel seismic imaging, Seismic reflector characterization around tunnels, 3D Image Point migration, VIBSIST seismic source.

ONKALO TUNNELIN 3D SEISMISET TUTKIMUKSET, OLKILUOTO 2013

TIIVISTELMÄ

POSIVA Oy suorittaa kallioperätutkimuksia käytetyn ydinpolttoaineen loppusijoitus-alueella Olkiluodossa, Eurajoella. Tutkimus- ja kehitystyön tarkoitus on varmistaa loppusijoituksen pitkäaikaisturvallisuuden vaatimusten noudattaminen. Maan pinnalta on louhittu ajotunneli maanalaiseen tutkimustilaan, ONKALOON. ONKALOSSA tehtävät tutkimukset keskittyvät kallioperän ja siinä esiintyvän pohjaveden olosuhteisiin loppusijoitustilojen alueella, ja rakentamisen vaikutukseen näihin tekijöihin. Deformaatiovyöhykkeet ja vettä johtavat vyöhykkeet voivat rajoittaa loppusijoitus-tunnelien ja -reikien sijoittelua. Tässä raportissa esitetyn seismisen tunnelitutkimuksen päätavoite on kehittää seismistä tutkimustekniikkaa loppusijoitusalueen karakterisoimiseksi. Kenttätyöt sisälsivät 3 vastaanotinlinjaa, joissa käytettiin 3-komponettisia geofoneja sekä yhteensä 12 lähdeprofiilia, joissa kuudella profiililla käytettiin Vibsist-500 lähdettä, yhdellä Vibsist-20 lähdettä ja viidellä mekaanista kairanreikävasaraa MH-70. Seismisten kenttätöiden suunnitelma perustui aiempiin seismisiin tunnelitutkimuksiin (Cosma et al. 2008 and 2011) ja ennen tutkimusta tehtyyn numeeriseen mallinnukseen (Heinonen et al. 2013). Tutkimus suoritettiin ONKALON demonstraatio-alueella kesäkuussa 2013. Useista lähde-vastaanotin pareista pitkin tunnelia ja kairanreikiä koostettiin yhdistetty aineisto, jolle suoritettiin P-aaltojen ensisaapujien tomografinen inversio. Näin saatu nopeusjakauma varmistettiin vertaamalla tuloksia suoran mallinnuksen avulla määritettyihin profiileihin. Image Point (IP) migraation avulla voidaan koostaa aika-etäisyys alueessa mitatut heijastusamplitudit IP alueeseen. Tällä tavoin voidaan vahvistaa koherenttia takaisinsirontaa. Tuloksena tuotetaan jokaisen vastaanotinlinjan ympärille haluttuun suuntaan 3D IP -prosessoidut seismiset profiilit. Tässä raportissa kuvattuja seismisiä tutkimuksia käytettiin kallioperässä esiintyvien deformaatiovyöhykkeiden ja merkittävien rakojen karakterisointiin. Tämä havainnol-listaa seismisten heijastustutkimusten mahdollisuuksia havaita, paikantaa ja suunnata erilaisia geologisia piirteitä. Tässä työssä 3D IP-migraatio oli tärkeä työväline. Lopuksi heijastuspiirteiden tulkintaa tehtiin suoran mallinnuksen avulla osittain vertaamalla tunnettuihin geologisiin rakenteisiin. Mittaustulokset ovat korkealaatuisia vaikka työskenneltiin tunneliolosuhteissa. Mitatun aineiston laatua saatiin parannettua käyttämällä kipsiä geofonien ja kallion kontaktin parantamiseen vastaanotinrei'issä. Suuri määrä heijastajia saatiin esiin usealla profiililla ja monet heijastajista voitiin suoraan yhdistää tunnettuun geologiseen rakenteeseen. Avainsanat: seisminen heijastusluotaus, 3D seismiset tutkimukset, seismisten heijastajien karakterisointi, 3D IP-migraatio, VIBSIST seisminen lähde.

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TABLE OF CONTENTS

ABSTRACT

TIIVISTELMÄ

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

2 FIELD WORK.......................................................................................................... 5

2.1 Survey layout ................................................................................................. 6

2.2 Equipment ...................................................................................................... 9

2.2.1 The VIBSIST-500 seismic source ...................................................... 9

2.2.2 The MH-DW70 mechanical borehole hammer ................................. 10

2.2.3 Receivers and recorder .................................................................... 10

3 DATA PROCESSING ........................................................................................... 13

3.1 Data quality and frequency analysis ............................................................ 13

3.2 Preconditioning of the data profiles .............................................................. 14

3.3 Tomographic inversion ................................................................................. 23

4 RESULTS ............................................................................................................. 29

4.1 3D Image Point migration ............................................................................ 29

4.2 Migrated sections ......................................................................................... 30

4.3 Reflector interpretation ................................................................................. 37

5 DISCUSSION........................................................................................................ 53

6 REFERENCES ..................................................................................................... 55

APPENDIX A. KNOWN STRUCTURES INTERPRETED FROM SEISMIC DATA ...... 57

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3

1 INTRODUCTION

POSIVA Oy conducts bedrock investigations at the spent nuclear fuel final disposal site at Olkiluoto, in western Finland. The purpose of these efforts, which include a significant R&D component, is to ensure compliance with the requirements set forth for the long-term safety of final disposal. The excavation of the access tunnel to the repository hosts the ONKALO underground rock characterization facility. The investigations carried out in ONKALO focus on the bedrock and groundwater conditions prevailing on the final disposal site and how construction work affects them. Deformation zones and hydraulically conductive zones can limit the areas which are suitable for a deposition hole to be placed. Therefore, it is important to develop techniques to characterize these areas before the excavation process begins so they can be taken into account. The main objective of the tunnel seismic investigations carried out in 2013 and presented here is to develop a seismic investigation technique for deposition area characterization. This investigation will develop and test seismic reflection surveys and processing methods which can be used to characterize deformation zones and large fractures in the pre-excavation phase of deposition tunnels. This method can provide information on the orientation and extent of the features in question. The field work consisted of 3 receiver lines using 3-component geophones and sources locations using the Vibsist-500 for 6 profiles, the Vibsist-20 for 1 profile (sparse), and a mechanical borehole hammer, MH-70, for 5 profiles for a total of 12 profiles. This investigation took place in the ONKALO demonstration area (Figure 1). Design of the seismic field work is based on previous tunnel seismic works in ONKALO (Cosma et al. 2008 and 2011) and pre-survey numerical modeling for field data and processing (Heinonen et al. 2013).

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Figure 1. Location of the 2013 3-component seismic surveys in the ONKALO tunnel.

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2 FIELD WORK

The fieldwork was carried out in June 2013, as shown in Table 1. Vibrometric field personnel and their responsibilities are presented in Table 2. The work was supervised by Antti Joutsen from Posiva Oy and Eero Heikkinen from Pöyry Oy.

Table 1. Fieldwork time schedule.

No. Day No. of shots Remarks 1 27.05.13 - Site specific training 2 28.05.13 - Olkiluoto site training 3 29.05.13 - Start-up meeting & begin setup 4 30.05.13 - Setup & calibration of equipment

5 31.05.13 2 Plastering geophones for Line 1 & noise tests. Two source locations

5 03.06.13 83 Production for Line 1 6 04.06.13 26 Production for Line 1 7 05.06.13 - Setup & calibration of borehole hammer 8 06.06.13 44 Production for Line 1 in PH23

9 07.06.13 34 Production for Line 1 in PH23 and PH21. Hammer getting obstructed in PH21

10 08.06.13 6 Hammer installed back in PH21 and obstructed again. Could not retrieve from hole.

11 09.06.13 - Retrieved hammer from PH21. Maintenance at Vibrometric’s base

12 10.06.13 40 Production on Line 1 using Vibsist-250

13 11.06.13 36 Completed Line 1 production. Moving spread

14 12.06.13 - Finish setup of Line 2, plastering geophones & tests

15 13.06.13 67 Production Line 2

16 14.06.13 15 Production Line 2. Repeat of bad source locations

17 17.06.13 35 Production Line 2 in PH21. Setup of borehole hammer

18 18.06.13 38 Production of Line 2 in PH21 19 19.06.13 70 Production of Line 2 in PH23

20 20.06.13 10 Production of Line 2 & moving spread to Line 3

21 21.06.13 - Setting up Line 3, plastering geophones 22 22.06.13 80 Production of Line 3 23 23.06.13 76 Production of Line 3

24 24.06.13 32 Production of Line 3 in PH27 & begin demobilization

25 25.06.13 - Demobilization

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Table 2. Vibrometric field personnel and responsibilities.

Name Responsibility Authority

Calin Cosma Survey design, Acquisition QC, Data processing & Reporting

Project manager

Nicoleta Enescu Survey design, QC, Data processing & Reporting

Contact Person

Cristian Vasile Field operation

Jonathan Crawford Equipment setup, Data acquisition and processing, Reporting

Dan Stanescu Equipment setup, Data acquisition Alexandru Prisaciuc Field operation

2.1 Survey layout

The survey was conducted at a depth of ~420 m in the demonstration area of the ONKALO tunnel. It consisted of 3 receiver lines with 77-80 3 component geophones and source locations along 12 different lines using the Vibsit-500, Vibsist-20, and Mechanical Borehole hammer. The receiver lines were placed in Ajoneuvoyhteys 11 right wall (A11R), ONKALO Access tunnel left wall, and Demonstration Tunnel (DT2R) right wall. The geophones were spaced 50 cm apart in A11R and ONKALO Access Tunnel and 1 m apart in DT2R. The geophones are place in 20 cm holes drilled in the tunnel wall and were secured with gypsum plaster to create a good contact between the geophone and wall. Source locations that were along the same walls as the receivers were placed 50 cm above the receivers. The spacing between receiver locations and source locations can be seen in detail in Table 3.

Table 3. Survey Parameters.

Sources Receivers Location # Spacing(m) Length(m)Location # Spacing(m) Length(m)A11R 85 0.44-1.05 45.39 A11R 80 0.44-0.59 40.30

A5L 26 0.99-1.04 25.14 ONKALO Access Tunnel 77 0.57-0.87 57.03

PH21 72 0.99-1.00 72.01 Demo Tunnel 2 78 0.99-1.03 77.29 PH23 72 0.99-1.00 71.25 Onkalo Access Tunnel 77 0.66-0.91 57.63 Demo Tunnel 2 80 0.81-1.20 79.61 Demo Tunnel 1 11 1.39-1.62 15.17 A11L 65 0.49-0.53 46.01 PH27 32 0.49-0.50 15.52

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A naming convention was created to organize the different combinations of sources and receivers used in this survey. Table 4 explains the locations of both the receivers and sources for each profile. These names will be used for the remainder of the report to describe the different profiles. Figures 2-4 show the layout of these profiles.

Table 4. Naming Convention for the measured sections.

Receiver Location Source Location Profile Name A11R PH21 L11 A11R PH23 L12 A11R A11R L13_s_1_85 A11R A5L L13_s_86_111 A11R ONKALO Access Tunnel L14 ONKALO Access Tunnel PH21 L21 ONKALO Access Tunnel PH23 L22 ONKALO Access Tunnel ONKALO Access Tunnel L23 DT2R DT2R L31 DT2R A11L L32 DT2R PH27 L33 DT2R DT1R L34

Figure 2. Line 1 Layout. Consists of 80 receivers in A11R with source locations in PH21, PH23, A11R, A5L, and ONKALO Access Tunnel.

Detectors Boreole Source Vibsist Source

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Figure 3. Line 2 layout. Consisting of 77 receivers in ONKALO Access Tunnel and sources in PH21, PH23, and ONKALO Access Tunnel.

Figure 4. Line 3 layout. Consisting of 78 receivers in DT2R and sources in DT2R, DT1R, A11L, and PH27.

Detectors Borehole Source Vibsist Source

Detectors Borehole Source Vibsist Source

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2.2 Equipment

2.2.1 The VIBSIST-500 seismic source

A time-distributed swept-impact, the Vibsist-500 hydraulic source, was used for 6 of the profiles (Figure 5).

Energy: 500 J/impact Impact rate: 3 - 20 impacts / sec Impact head: steel rod Hydraulic flow: 15 - 30 l / min Pressure: 150 bar Trigger by accelerometer that was place on the wall beside where the hammer

was hitting The VIBSIST-500 is based on the Swept Impact Seismic Technique (SIST), for which the seismic signals are produced as a series of pulses, according to a specific pre-programmed sequence. The use of the monotonous variation of the impact rate controls effectively the non-repeatability of the impact intervals and achieves a wide bandwidth even when the coupling to the rock or ground is relatively poor.

Figure 5. The Vibsist-500 seismic source used for the ONKALO measurements.

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2.2.2 The MH-DW70 mechanical borehole hammer

The mechanical borehole hammer was used for 5 different profiles. The hammer uses motor-driven springs to release a weight that creates the seismic wave. It propagates through 3 "wedges" that are mechanically controlled to expand outwards from the hammer to make good contact with the walls of the borehole. This source was used to create 10 separate impacts and 10 separate seismograms which were then stacked to increase coherency. This hammer can create up to 300 J/impact. An electronic module is used to start and stop the impacts and clamp and unclamp the wedges.

Figure 6. The MH-DW70 seismic source used for the ONKALO measurements in the boreholes.

2.2.3 Receivers and recorder

Receiver holes were drilled prior to the survey, horizontally into the tunnel wall at ~ 1 m from the ground and were ~40 cm deep. Each borehole was instrumented with a custom made 3-component receiver equipped with OyoGeospace SMC1850/30Hz geophones oriented as follows: the X component vertical, the Y component horizontal along the tunnel axis and Z the component horizontal, perpendicular to the tunnel wall, as shown in Figure 7. These were installed in the short holes drilled on the tunnel wall, being secured, for good contact, with gypsum plaster. The seismograms were recorded on a Summit II Plus 24-bit seismic data recording system with 241 channels (Figure 8), and subsequently decoded to produce 0.25 s seismic traces. Each Summit II Plus module has two channels and 3 of these modules were placed in a bag for a total of 6 channels per bag. These bags were hung on hooks that were placed between every 2nd receivers so 1 bag contained enough channels for two 3-component receivers. Table 5 and Table 6 show the technical specifications and parameters of the recording system respectively.

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Figure 7. Illustration of a hole where one three components receiver was mounted.

Figure 8. Seismic acquisition in the ONKALO tunnel.

Figure 9. Receiver bag setup for ONKALO

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Table 5. Technical specifications of the Summit II Plus system.

Table 6. Registration parameter of the Summit II Plus system.

Registration parameter Value for Vibsist-500 Value for MH-DW70 Sample rate (ms) 0.100 0.100 Trace length (ms) 23680 256 Pre-trigger (ms) 10 10 No. of channels 241 241 No. of sweeps 2 10 (stacks)

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3 DATA PROCESSING

3.1 Data quality and frequency analysis

The data was analyzed for possible malfunctions of the system like high noise levels, coordinates location errors, time delays and trace order. Errors, when found, were corrected. In order to do this, trace inspection and spectral analysis of the data has been carried out. Typical amplitude spectra for Vibsist-500, for source 21 of L23, is shown in Figure 10. Figure 11 displays the average spectra for the mechanical borehole hammer, L21 source 29.

X

Y

Z

Figure 10. Amplitude frequency spectra analysis for L23, source 21 (Vibsist-500).

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X

Y

Z

Figure 11. Amplitude frequency spectra analysis for L21, source 29 (MH70).

3.2 Preconditioning of the data profiles

Data were automatically decoded by the VIBSIST shift and stack procedure. A few shot gathers needed to be re-stacked due to malfunctioning of the pilot trace recording. Both the Vibsist and the borehole hammer profiles were processed in similar manner to keep the procedure consistent for the entire project. Pre-processing and data conditioning tasks with relevant parameters are presented in Table 7. For comparison reasons all the examples shown in this section are made for L23 and L21.

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Table 7. Pre-Processing and data conditioning tasks and parameters.

TASK DESCRIPTION KEY INPUT VALUES

1 SHIFTRA Static corrections Picked times after corrections for Vibsist profiles only

2 FILTER Band-pass filter 500 Hz -1500 0-phase

3 ADECAY Equalizes amplitudes by distance from source

Coefficient of 1.25

4 SPECTRA Calculates the amplitude spectra

5 HARMON Removes harmonic ringing (seen mostly of X-component)

25 frequencies, 10 Hz separation

6 AGC Equalizes amplitudes, saves gains

200 samples window

7 CNOISEOFF Suppress S-waves and Tunnel waves multiples

21 trace panel, on source gather, v= 3000-3200 m/s

8 CNOISEOFF Suppress S-waves and Tunnel waves multiples

21 trace panel, on detector gather, v= 2900-3600 m/s


10 CNOISEOFF Suppress S-waves 7 trace panel, -4 ms to 15 ms from estimate. On source and detector gather.

11 CNOISEOFF Suppress S-waves 41 trace panel, 15 ms from estimate to end of trace. On source and detector gather


13 CNOISEOFF Suppresses P wave first arrivals11 trace panel, on receiver and source gather, static corrected picked times, -5 ms to 10 ms from estimate.

14 SR&DTCHG Cut file Cut of pretrigger, cut length to 150 ms

15 ADDMUL Multiply output (14) with gain (6)

Multiply, scale=1


100 samples window

17 CNOISEOFF Suppress ringing 17 trace panel, on gain output from (16)

18 ADDMUL Multiply output (16) with median (17)

Multiply, scale=1


3-component AGC to be used for migration

20 SHIFTRA Static corrections First arrivals shifted to 5750 m/s Data pre-processing, not included in Table 7, consisted of:

Separation of the three components vertical (X), horizontal (Y) and perpendicular to the wall (Z) from the 240 channels records.

Incorporation of the geometric information into the data files. Frequency analysis and filtering. The main frequency band of the S and P

waves was estimated to be 500-1500 Hz. Frequencies below 500 Hz were low frequency ringing and tunnel wave noise.

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The following figures show the progression of the preconditioning of the data to be used for migration. In these images it can be seen that before any processing the S-waves, tunnel waves, and P-waves dominate the profile but after processing they have been removed very well.

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X

Y

Z

Figure 12. L23 Vertical component (X), horizontal component (Y), perpendicular to the tunnel wall component (Z), source 21 before any processing.

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X

Y

Z

Figure 13. L23 Vertical component (X), horizontal component (Y), perpendicular to the tunnel wall component (Z) for source 21 after removal of S-waves and tunnel waves.

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X

Y

Z

Figure 14. L23 Vertical component (X), horizontal component (Y), perpendicular to the tunnel wall component (Z) for source 21 after removal of P-waves.

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X

Y

Z

Figure 15. L21 Vertical component (X), horizontal component (Y), perpendicular to the tunnel wall component (Z) for source 29 before any processing.

21

X

Y

Z

Figure 16. L21 Vertical component (X), horizontal component (Y), perpendicular to the tunnel wall component (Z) for source 29 after removal of S-waves and tunnel waves.

22

X

Y

Z

Figure 17. L21 Vertical component (X), horizontal component (Y), perpendicular to the tunnel wall component (Z) for source 29 after removal of P-waves.

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3.3 Tomographic inversion

Tomographic inversion of P-wave first arrival times was done on two combined data sets, one containing all arrival times from Line 1 (A11R) and 2 (ONKALO Access Tunnel) together and another one containing all arrival times from Line 3 (DEMO Tunnel 2). Arrival times were picked on all measured profiles, with the best possible accuracy. An initial P-wave velocity distribution was estimated from the arrival times measured on data sets with the source in boreholes, as these source positions were not be influenced by EDZ and are more representative for velocity estimates in the investigated rock block. Once the initial velocity distribution was computed, the first arrival times were estimated for all the measured profiles to generate time estimates and create a ray structure in the investigation plane. For all profiles measured with the source on the tunnel wall, the P-wave picked times were adjusted considering the estimates derived from the velocity distribution obtained by inversion. Finally, all picked P-wave first arrival times were concatenated in the 2 sets, one including all profiles measured along Lines 1 and 2 (Figure 2 and Figure 3) and another including all profiles measured along Line 3 (Figure 4). The final P-wave velocity distribution was computed by tomographic inversion from these 2 time sets using the ray structure determined in the first stage of inversion and a constraint of the velocities in the 3000-6000 m/s velocity range. The results are shown in Figure 18 and Figure 19.

Figure 18. P-wave velocity distribution derived by tomographic inversion from times measured on Lines 1 and 2. Velocity range is shown from 5600 to 6000 m/s.

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Lower velocities that appear near tunnel edges, as displayed in Figure 18, may be associated to the presence of EDZ, while throughout the rest of the rock, in the tomographic plane, we observe a fairly homogeneous velocity distribution. An exception to this is the slightly slower velocity extending further into the wall around the middle of the Line 1 receivers. Similarly to the velocity distribution determined from the Lines 1 & 2 data, lower velocity, which may be associated to the presence of EDZ, is also observed along the receiver positions, as well as, the rock between Demo Tunnel 2 and Demo Tunnel 1, for the velocity distribution derived from the Line 3 data set. The lower velocity zone which extends further into the rock near the end of the receiver line (top left of the tomogram shown in Figure 19) may be due to a combination between the presence of EDZ along the tunnel and poor ray coverage in that corner.

Figure 19. P-wave velocity distribution derived by tomographic inversion from times measured on Lines 3. Velocity range is shown from 5600 to 6000 m/s.

The velocity distributions derived by tomographic inversion were verified by comparing the arrival times forward modeled using them and the associated curved ray paths with the arrival times picked on each measured profile. Figures 20-28 present examples of this comparison on 4 separate measured profile, displaying images of both shot and receiver gathers.

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Figure 20. L12 source 40 (all receivers). Modeled times in black, picked times in green.

Figure 21. L12 receiver 36 (all sources). Modeled times in black, picked times in green.

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Figure 22. L14 source 1. Modeled times in black, picked times in green.

Figure 23. L14 receiver 70. Modeled times in black, picked times in green.

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Figure 27. L31 receiver 49. Modeled times in black, picked times in green.

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4 RESULTS

4.1 3D Image Point migration

A 3D Image Point migration (Cosma et al., 2010) algorithm was used to create 3D oriented migrated sections from all data profiles measured in ONKALO. The Image Point (IP) migration method is characterized by its ability to accumulate reflection events measured in the time distance data sets into points in the IP domain (Figure 28). In the IP space, coherency enhancement is achieved two fold, firstly because non-coherent noise migration artifacts and coherent patterns due to other wave types and multiples are suppressed, and secondly by 3D point cluster building. Therefore, reflections from segments of planes with transverse dimensions larger than a few wavelengths are enhanced.

Figure 28. Illustration of the 3D IP migration process. The wave front produced at the Source Sm is reflected at point V before reaching the receiver Rn. The orientation of the reflector P at point V is uniquely determined by the source - receiver geometry and the velocity field. The planar reflector P is in turn uniquely associated with the point IP, defined as the reflected image of the origin O on the plane P. Using all the processed data sections, the following steps were used to calculate the oriented 3D migrations:

1. Create a 3D structure, migration space, using a set of geometrical parameters (X, Y and Z), to define the extent of each migrated section and its coverage, with a cell size of 0.5 x 0.5 x 0.5 meters.

2. Create the Image Point space, using cylindrical coordinates (as shown in Figure 28) and the velocity model determined by tomographic inversion.

3. Filter and enhance the IP space 4. Compute the migrated sections, from the 3D IP space calculated for each

measured data set. 5. Where appropriate, perform geometrical stack in 3D space coordinates of

individual migrations obtained in step 4.

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The result of the 3D IP migration consists of migrated sections oriented to preferred azimuths, selected this time to coincide with the investigation plane, containing both the source and receiver locations. The main section corresponds to 0°, while a flipped section was also computed at 180°, where relevant.

4.2 Migrated sections The results of the entire processing exercise are the 3D migrated sections, computed in a horizontal plane, around each receiver line and displayed in Figure 29 to Figure 42. These were used for interpretation, to generate a 3D map of the main identifiable structures, which may be further correlated with geological structures such as faults, fractures or lithological contacts.

Figure 29. L11 migrated section (0° & 180°), investigation layout as shown in Figure 2.

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Figure 33. L11 and L21 migrated sections (added, 0° & 180°).

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Figure 34. L13_s_1_85 migrated section (0°), investigation layout as shown in Figure 2.

Figure 35. L13_s_86_111 migrated section (0°), investigation layout as shown in Figure 2.

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Figure 37. L23 migrated section (0°), investigation layout as shown in Figure 3.

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Figure 38. L31 migrated section (0°), investigation layout as shown in Figure 4.


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Figure 42. L32, L33, and L34 migrated sections (added, 0° and 180°).

4.3 Reflector interpretation

The interpretation phase consists, mainly, of computing the 3D locations and orientations of the main reflectors, by using the velocity determined as part of the processing and the measured coordinates of the shot points and receivers. To this point, the results of previous investigations and the current site model were not used; the geometrical estimates being obtained by cross fitting amongst migrated sections.

The 3D target localization cannot be done unambiguously from a single line of shot points and receivers because of the non-determination of the azimuth of a reflector. Such ambiguity may be removed if the shot - receiver geometry is diverse, with respect to the orientation of the target. The result of the cross fitting procedure are presented in Figure 43 to Figure 49. The interpreted reflectors are marked with colored lines on the migrated sections and labeled with reflector numbers, as presented on the first column in Table 9. Reflectors were picked and classified based on their continuity within each profile and persistence from profile to profile. This applies to events corresponding to features with a lateral extent comparable with or larger than the typical wavelength, which has been in this case about 5m.

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A practical approach to resolving the site geometry relies on the simultaneous interactive fitting among several profiles measured along different tunnels or boreholes and migrated at different angles around those. The dip direction estimate is obtained by comparing migrated sections computed at different orientations around a tunnel. Theoretically, a reflector imaged in a migrated section is perpendicular on that section, though some variability appears. The first column in Table 9 is the event number, which is the same as the label of the reflector curves shown in the profiles displayed in Figure 43 to Figure 49. The width of the reflective elements shown in the 3-D plots of Figure 50 to Figure 56 is 5m, which corresponds to +/- one mean wavelength. The second column is the Length (m) from a reference point along the tunnel (given in Table 10) to the reflector intersection with the tunnel (or its extension) around which the data was migrated. This parameter is relevant for interpretation only for the reflectors actually intersecting the tunnel. For the others, it is only a mathematical way of describing the position of the reflector relative to the tunnel axis. The interpreted dips of the reflectors are given in the third column and the dip directions in the fourth column. These were determined interactively, in several steps, seeking the best reflector fit among all interpreted migrated sections. In each profile, reflectors are classified in three categories. Major events, appearing as well defined and continuous, belong to the first category (Visibility mark = 2). The weaker reflectors, visible but overridden by stronger events of other orientations belong to the second category (Visibility mark = 1). If the position and orientation of an event are determined from other profiles but the event does not appear as visible in the current profile, it is categorized as a third class (Visibility mark = 0). The profile where a reflector is visible is given in the fifth column, while its visibility appears in the eighth column of Table 9. The sixth and seventh columns list the extent where the reflector is visible on the migrated section, by giving the first and last trace where the reflector is observed. Since the migrated sections are computed in the 3D space, the difference between these two numbers gives the observable length of the reflector, considering that the distance between two traces in the migrated sections is 0.5m. Columns 9th to 11th in Table 9 give the coordinates of the crux point that, together with the coordinates of the Origin chosen for interpretation, fully characterizes the reflector element. For all seismic data interpreted the origin for interactive interpretation (Crux origin) is given in Table 8. Having a common origin facilitates further integration of interpreted reflectors, among several profiles measured from boreholes or from surface.

39

Table 8. Reflector interpretation conventions.

Reflector Visibility 2 Clear

1 Weak

0 Not visible

Crux origin N

Crux origin E

Crux origin elevation

2189.20 5762.54 -420.92

Figure 43. Horizontal migrated sections (0° on the left and 180° on the right) computed from the 2D data recorded in L11 and L12, with the interpreted reflector marked with coloured lines.

40

Figure 44. Horizontal migrated sections (0° on the left and 180° on the right) computed from the 2D data recorded in L21 and L22, with the interpreted reflectors marked with coloured lines.

41

Figure 45. Horizontal migrated sections (0° on the left and 180° on the right) computed from the 2D data recorded in, with the interpreted reflectors marked with coloured lines.

Figure 46. Horizontal migrated sections (0° on the left and 180° on the right) computed from the 2D data recorded in L32, L33, and L34, with the interpreted reflectors marked with coloured lines.

42

Figure 47. Horizontal migrated sections (from sources 1-85 on the left and from sources 86-111 on the right) computed from the 2D data recorded in L13, with the interpreted reflectors marked with coloured lines.

Figure 48. Horizontal migrated sections (0° on the left and 180° on the right) computed from the 2D data recorded in L23, with the interpreted reflectors marked with coloured lines.

43

Figure 49. Horizontal migrated sections (0° on the left and 180° on the right) computed from the 2D data recorded in L31, with the interpreted reflectors .marked with coloured lines.

The following images show various 3D views of the interpreted reflector elements. The solid blue lines mark the source and receiver locations, while the thick black lines mark outlines of the tunnels in the investigation area.

Figure 50. Interpreted 3D reflector elements, together with L11 and L12 migrated sections.

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Figure 51. Interpreted 3D reflector elements, together with L12 and L22 migrated sections.

Figure 52. Interpreted 3D reflector elements, together with L13 migrated sections.

45



46


Figure 56. Interpreted 3D reflector elements, together with L32, L33, and L34 migrated sections.

47

Table 9. Interpreted Reflector Parameters.

Refl # Intersect

length (m) Dip (°)

Dip Dir (°)

Profile 1st rec.

Last rec

Visibility

Crux N Crux E Crux El

1 -377.68 48 160 L11&L21_000 1 40 1 2224.1 5749.9 -454.3

1 -377.68 48 160 L11&L21_180 1 45 2

1 -899.82 48 160 L12&L22_000 1 50 2

1 -899.82 48 160 L12&L22_180 1 60 2

1 99.84 48 160 L12_86_111 65 110 2

1 -79.84 48 160 L13_1_85 1 30 1

1 179.91 48 160 L14_000 145 200 1

1 -147.23 48 160 L23 1 33 1

1 100 48 160 L32&33&34_000 65 165 1

2 76.71 37 198 L11&L21_000 40 140 1 2204.3 5767.4 -442

2 76.71 37 198 L11&L21_180 93 150 1

2 120 37 198 L12&L22_000 22 93 2

2 120 37 198 L12&L22_180 65 145 1

2 37.51 37 198 L12_86_111 35 70 2

2 -17.51 37 198 L13_1_85 1 45 2

2 117.44 37 198 L14_000 120 180 2

2 117.44 37 198 L14_180 135 200 1

2 -827.83 37 198 L23 25 125 1

2 -63.3 37 198 L31 1 120 2

2 154.68 37 198 L32&33&34_000 55 100 1

3 407.98 89 280 L13_1_85 60 120 2 2200.8 5697 -419.8

3 -308.85 89 280 L14_000 1 70 1

3 -308.85 89 280 L14_180 10 80 1

3 77 89 280 L32&33&34_000 60 115 1

3 77 89 280 L32&33&34_180 100 155 2

4 -84 80 258 L14_000 1 39 1 2174 5691.2 -408.1

4 -84 80 258 L14_180 1 40 2

4 -28.67 80 258 L31 1 90 1

4 118.4 80 258 L32&33&34_180 50 140 2

5 245.39 89.8 274 L13_1_85 60 120 2 2192.9 5710.2 -420.7

5 -146 89.8 274 L14_000 6 75 2

5 -146 89.8 274 L14_180 1 70 2

5 59.72 89.8 274 L32&33&34_180 57 118 2

6 513.72 54 174 L12&L22_000 1 90 2 2200.8 5761.3 -429.4

6 513.72 54 174 L12&L22_180 1 70 1

6 24.99 54 174 L12_86_111 65 111 1

6 -4.99 54 174 L13_1_85 1 40 1

6 105 54 174 L14_000 115 165 1

6 105 54 174 L14_180 140 200 1

6 -112.7 54 174 L23 1 35 2

48

(continuation of Table 9)

Refl # Intersect

length (m) Dip (°)

Dip Dir (°)

Profile 1st rec.

Last rec

Visibility


7 -1559.06 51 165 L12&L22_180 1 60 2 2204.7 5758.4 -433.9

7 41.96 51 165 L12_86_111 25 75 2

7 -21.96 51 165 L13_1_85 1 45 2

7 122.01 51 165 L14_000 105 185 2

7 122.01 51 165 L14_180 138 200 2

7 -100.32 51 165 L23 1 60 2

7 29.88 51 165 L31 45 60 2

55 104.67 45 100 L13_1_85 45 85 2 2188.8 5764.9 -418.6

55 -5.73 45 100 L14_000 59 106 1

55 21.73 45 100 L23 25 75 1

55 -15.63 45 100 L32&33&34_180 1 40 1

56 -54.57 71 180 L11&L21_000 1 400 2 2183.9 5762.5 -419.1

56 -64.36 71 180 L11&L21_180 1 70 2

56 24.79 71 180 L13_1_85 50 60 1

56 75.2 71 180 L14_000 125 150 2

56 75.2 71 180 L14_180 130 150 2

56 -77.37 71 180 L23 1 55 2

56 31 71 180 L32&33&34_000 5 60 2

8 33.84 84.3 244.7 L12_86_111 35 60 2 2207.4 5801 -425.2

8 -13.84 84.3 244.7 L13_1_85 1 50 2

8 113.59 84.3 244.7 L14_000 145 200 2

8 113.59 84.3 244.7 L14_180 140 200 2

8 151.4 84.3 244.7 L23 106 157 2

8 364.54 84.3 244.7 L31 100 200 2

8 -270.24 84.3 244.7 L32&33&34_000 1 50 2

9 -21.73 50 31.35 L12&L22_180 1 45 1 2175.8 5754.4 -434

9 55.68 50 31.35 L13_1_85 65 111 2

9 -262.27 50 31.35 L23 25 125 2

10 20 28 168 L31 54 112 1 2195.7 5761.2 -433.5

11 974.39 60 211 L23 30 120 2 2180.3 5757.2 -415

11 27 60 211 L31 60 117 2

11 62.7 60 211 L32&33&34_180 1 70 1

12 -237.08 14 163 L23 20 120 2 2191.9 5761.7 -432.2

12 91 14 163 L32&33&34_180 15 125 2

13 83.25 65 55 L13_1_85 90 120 2 2171.5 5737.3 -435.3

13 126 65 55 L32&33&34_180 40 161 2

14 -60.96 87 10 L11&L21_180 1 65 2 2175.6 5760.1 -421.6

14 -92.12 87 10 L23 30 80 2

14 29 87 10 L32&33&34_000 1 57 2

49


Refl # Intersect

length (m) Dip (°)

Dip Dir (°)

Profile 1st rec.

Last rec

Visibility


15 97.68 75 60 L12&L22_000 135 170 2 2234.3 5840.6 -396.8

15 97.68 75 60 L12&L22_180 130 170 2

16 74 87 305 L11&L21_000 45 90 2 2150.3 5818.2 -424.5

16 74 87 305 L11&L21_180 90 153 2

16 259.4 87 305 L13_1_85 40 120 2

17 10 69 185 L11&L21_180 30 110 2 2195 5763.1 -423.2

17 143.08 69 185 L12&L22_000 15 95 2

17 88.07 69 185 L14_000 150 170 2

17 88.07 69 185 L14_180 150 175 2

17 -130.91 69 185 L23 1 55 2

18 -92.54 82 325 L11&L21_000 1 25 2 2214.5 5744.8 -416.6

18 -92.54 86.5 324.2 L11&L21_180 1 20 2 2215.4 5743.7 -419

18 91.85 86.5 324.2 L12_86_111 55 85 2

18 -71.85 86.5 324.2 L13_1_85 1 50 2

18 172.06 86.5 324.2 L14_000 117 190 2

19 158.51 87.1 292.8 L11&L21_180 235 289 2 2130.4 5902.4 -428.5

19 130.87 87.1 292.8 L12&L22_180 190 230 2

20 159.89 87.9 282.5 L11&L21_180 282 320 2 2153.1 5926.1 -427

20 141.17 87.9 282.5 L12&L22_180 230 270 2

21 224.43 84 295 L11&L21_180 315 375 2 2104.2 5944.7 -442

21 193.38 84 295 L12&L22_180 255 315 2

22 241.22 85.5 292.4 L11&L21_180 360 400 2 2104.6 5968 -438.4

22 213.06 85.5 292.4 L12&L22_180 307 370 2

23 91.72 85.2 260.6 L11&L21_000 174 183 2 2207.2 5871.9 -430.2

23 88.01 85.2 260.6 L12&L22_000 176 177 2

23 169.82 85.2 260.6 L12_86_111 80 120 2

23 249.46 85.2 260.6 L14_000 180 200 2

23 249.46 85.2 260.6 L14_180 180 200 2 2207.2 5871.9 -430.2

24 132.44 85.3 257.6 L11&L21_000 256 264 2 2221.6 5910.1 -433.5

24 130.62 85.3 257.6 L12&L22_000 258 262 2

25 48.09 69.3 50.6 L11&L21_000 49 88 1 2221.5 5801.8 -401.7

25 69.64 69.3 50.6 L12&L22_000 55 129 2

25 51.02 69.3 50.6 L12_86_111 65 95 1

25 130.83 69.3 50.6 L14_000 180 200 2

25 365.91 69.3 50.6 L23 95 160 2

25 - n/a 69.3 50.6 L31 40 150 2

25 n/a 69.3 50.6 L32&33&34_000 20 85 1

50


Refl # Intersect

length (m) Dip (°)

Dip Dir (°)

Profile 1st rec.

Last rec

Visibility


26 124.03 79.7 186.6 L11&L21_000 1 55 2 2225.8 5766.8 -427.6

26 248.08 79.7 186.6 L12&L22_000 25 123 2

26 248.07 79.7 186.6 L12&L22_180 30 90 2

26 40.07 79.7 186.6 L12_86_111 66 80 2

26 -210.11 79.7 186.6 L23 1 35 2

26 -12.34 79.7 186.6 L31 1 60 1

26 102.43 79.7 186.6 L32&33&34_000 65 155 1

27 -128.82 87 8 L11&L21_000 1 45 1 2157.4 5758.1 -422.6

27 -128.82 87 8 L11&L21_180 3 64 2

28 79.19 87 274 L11&L21_000 130 160 2 2182.5 5858.8 -426

28 230.6 87 273.5 L12_86_111 60 110 2

28 -210.6 87 274 L13_1_85 1 32 2

28 310 87 274 L14_000 120 200 2

28 310 87 274 L14_180 106 198 2

29 101.02 70.5 207.1 L11&L21_000 30 90 1 2245.2 5791.2 -443.2

29 101.02 70.5 207.1 L11&L21_180 70 155 2

29 143.71 70.5 207.1 L12&L22_000 85 155 2

29 -179.26 70.5 207.1 L31 1 70 1

29 271.41 70.5 207.1 L32&33&34_000 69 149 2

30 -644.27 86.2 165 L11&L21_180 1 50 1 2252.8 5745.5 -425.3

30 -11.96 86.2 165 L31 1 25 1

30 102 86.2 165 L32&33&34_000 140 185 2

31 -81.38 86.7 161.8 L11&L21_180 1 65 1 2198.1 5759.6 -421.5

31 -316.84 86.7 161.8 L12&L22_000 1 70 2

31 -316.84 86.7 161.8 L12&L22_180 1 55 1

31 25.14 86.7 161.8 L12_86_111 60 90 1

31 -5.14 86.7 161.8 L13_1_85 1 40 1

31 105.21 86.7 161.8 L14_000 135 175 1

31 -59.73 86.7 161.8 L23 1 20 1

31 37.18 86.7 161.8 L32&33&34_000 48 68 2

32 -280.75 86.9 161.2 L11&L21_000 1 35 1 2231.1 5748.3 -423.3

32 -280.75 86.9 161.2 L11&L21_180 1 45 1

32 -501.09 86.9 161.2 L12&L22_180 1 30 1

32 72.56 86.9 161.2 L12_86_111 70 100 1

32 74.3 86.9 161.2 L32&33&34_000 126 149 2

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Refl # Intersect

length (m) Dip (°)

Dip Dir (°)

Profile 1st rec.

Last rec

Visibility


33 -110.34 87 157 L11&L21_000 1 25 1 2208.9 5754.2 -422

33 -110.34 87 157 L11&L21_180 1 70 2

33 -264.91 87 157 L12&L22_000 1 30 2

33 -264.91 87 157 L12&L22_180 1 47 2

33 -26.85 87 157 L13_1_85 1 30 1

33 126.95 87 157 L14_000 130 170 1

33 43.24 87 157 L31 77 87 2

33 46.72 87 157 L32&33&34_000 70 92 2

34 -207 89.1 158.1 L11&L21_000 1 35 1 2227.8 5747 -421.6

34 -207 89.1 158.1 L11&L21_180 1 40 1

34 74.08 89.1 158.1 L12_86_111 65 100 2

34 154.17 89.1 158.1 L14_000 170 200 1

34 21.41 89.1 158.1 L31 35 44 2

34 68.58 89.1 158.1 L32&33&34_000 111 135 2

35 158.14 86.8 223.6 L11&L21_000 166 234 2 2290.9 5859.6 -428.8

35 183.65 86.8 223.6 L12&L22_000 225 265 2

36 144.29 86.8 223.6 L11&L21_000 138 218 2

36 169.85 86.8 223.6 L12&L22_000 185 255 2

37 178.27 87.5 207.4 L11&L21_000 89 148 2 2292.7 5816.2 -426.1

37 226.98 87.5 207.4 L12&L22_000 180 250 2

38 175.63 88.1 241.7 L11&L21_000 283 320 2 2276.5 5924.6 -426.9

38 175.63 88.1 241.7 L11&L21_180 320 350 2

38 185.68 88.1 241.7 L12&L22_000 315 350 2

39 169.97 86.2 230.9 L11&L21_000 225 260 1 2292 5889.3 -431.7

39 188.24 86.2 230.9 L12&L22_000 261 330 2

40 295.93 86 156.2 L11&L21_000 1 90 2 2114.8 5795.3 -415.2

40 295.93 86 155 L11&L21_180 45 158 2 2109.8 5799.6 -414.8

40 -33.68 86 155 L14_180 1 32 2

41 392.89 85.3 156.5 L11&L21_000 1 85 2 2094 5803.9 -412.3

41 392.89 85.3 156.4 L11&L21_180 32 153 2

41 248.05 85.3 156.4 L12&L22_180 35 95 1

42 174.63 87.3 149 L11&L21_000 1 88 2 2126.3 5800.3 -417.5

42 174.63 87.3 149 L11&L21_180 55 131 2

42 77.73 87.3 149 L12&L22_180 25 145 1

43 325.79 87.3 155.1 L12&L22_180 20 118 2 2068.9 5818.3 -414.6

44 336.2 87.7 151.4 L11&L21_180 110 180 2 2083.4 5820.3 -416

44 226.97 87.7 151.4 L12&L22_180 20 121 2

52


Refl # Intersect

length (m) Dip (°)

Dip Dir (°)

Profile 1st rec.

Last rec

Visibility


45 106.13 87.1 287.5 L11&L21_180 181 212 2 2155.3 5870.2 -426.7

45 83.36 87.1 287.5 L12&L22_180 115 165 2

45 931.03 87.1 287.7 L12_86_111 1 80 2

45 -911.03 87.1 287.5 L13_1_85 1 60 2

45 1009.21 87.1 287.5 L14_000 75 155 2

45 1009.21 87.1 287.5 L14_180 70 140 2

46 125.34 87.1 286.9 L11&L21_180 195 248 2 2151.2 5887.6 -427.5

46 102.99 87.1 286.9 L12&L22_180 165 205 2

47 -664.87 88.8 222.7 L32&33&34_180 1 85 2 2102.2 5682.4 -418.4

48 793.69 88.7 227.4 L32&33&34_000 10 42 2 2194 5767.8 -421.1

49 -32.42 88.2 278 L32&33&34_000 1 22 2 2187.1 5777.6 -421.4

50 -85 88.1 212.7 L32&33&34_180 1 69 1 2140.1 5730.9 -419

51 -35.27 88.3 208.5 L32&33&34_180 1 100 1 2148.5 5740.4 -419.5

52 499.31 84.9 294.7 L12_86_111 1 45 2 2186.1 5769.2 -421.6

52 -479.02 84.9 294.7 L13_1_85 26 98 2 2186.1 5769.2 -421.6

52 585.68 84.9 294.7 L14_000 60 115 2 2186.1 5769.2 -421.6

52 97.51 84.9 294.7 L31 160 190 2 2186.1 5769.2 -421.6

53 80 85.6 224.5 L23 76 129 2 2167.6 5741.3 -418.6

54 n/a 84.5 293.3 L12_86_111 1 50 2 2204.4 5727.3 -417.3

54 n/a 84.5 293.3 L13_1_85 21 105 2 2204.4 5727.3 -417.3

54 n/a 84.5 293.3 L14_000 55 130 2 2204.4 5727.3 -417.3

Table 10. Coordinates for the reference points used to calculate the Length given in the second column of Table 9.

Profile Name Northing (m) Easting (m) Elevation (m) L11 2191.724 5782.290 -421.100 L12 2154.958 5791.828 -421.251 L13_s_1_85 2204.335 5791.240 -422.582 L13_s_86_111 2185.945 5783.420 -421.758 L14 2112.397 5752.343 -418.459 L21 2191.724 5782.290 -421.100 L22 2154.958 5791.828 -421.251 L23 2143.977 5739.704 -419.642 L31 2227.566 5691.677 -418.385 L32 2158.438 5749.281 -420.130 L33 2158.438 5749.281 -420.130 L34 2158.438 5749.281 -420.130

53

5 DISCUSSION

One of the tasks of the seismic survey carried out in the ONKALO access tunnel was to test the suitability of 2D / 3D reflection seismic for detecting and locating geological features of diverse character and orientations. The results obtained and described here proved this to be a successful test, as the seismic surveys done in 2013 could be used to characterize deformation zones and fractures present in the investigated rock mass. High quality results were obtained, while operating in tunnel working conditions. The use of the 3D IP migration algorithm was instrumental for the success of this imaging exercise. The migrated sections shown in Figure 29 to Figure 42 display several strong reflectors, which, were interpreted to form a set of 3D reflectors, where numerous reflectors were visible across multiple profiles. Several interpreted reflectors may be directly associated with known geological structures, supplied by Posiva, for verification during the interpretation process. These are shown in Appendix A. As with previous work performed in 2007 and 2009, creating a good and detailed model (or prediction) of the geological and hydrological features of the repository area requires that integrated modeling is carried out using all geological, hydrological and geophysical data. It is expected that this integrated approach will be done by Posiva Oy in order to update the current site model in the investigated area. By using the 3-component geophones with source locations along tunnel walls, as well as, within horizontal boreholes in the rock it was possible to image geological seismic reflectors at many different orientations. Using the gypsum plaster in the receiver holes allowed for good contact between the geophones and the tunnel wall which increased the quality of the data.

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55

6 REFERENCES

Cosma, C., Balu, L. & Enescu, N., 2010. 3D VSP migration by Image Point Transform, Geophysics, vol. 75, no. 3, May-June 2010; p. S121–S130, 10.1190/1.3396316. Cosma, C., Cozma, M., Balu, L. & Enescu, N., 2008. Rock mass seismic imaging around the ONKALO tunnel, Olkiluoto 2007, Posiva Working report 2008-64, 29p. Cosma, C. and Enescu, N., 2001. Characterization of fractured rock in the vicinity of tunnels by the swept impact seismic technique. International Journal of Rock Mechanics and Mining Sciences: 38, p. 815-821. Cosma, C., Enescu, N., Balu, L. and Jacome, M. 2011. ONKALO 3D Tunnel Seismic Investigations at Olkiluoto in 2009. Posiva Working report 2011-21, 76p. Cosma, C., Enescu, N. & Heikkinen, E., 2010. Very high resolution hard rock seismic imaging for Excavation Damage Zone characterization. Near Surface 2010 – 16th European Meeting of Environmental and Engineering Geophysics Zurich, Switzerland, 6 - 8 September 2010. Cosma, C., Enescu, N., Lahti, M., Heikkinen, E. and Ahokas T., 2010. High Resolution 3D Tunnel Seismic Reflection at Olkiluoto, Finland. 72nd EAGE Conference & Exhibition, Barcelona, Spain, 14 - 17 June 2010, M035. Heinonen, S., Enescu, N., Danesh, A. and Heikkinen, E., 2013. Memo: Seismic Forward Modeling in Olkiluoto.

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57

APPENDIX A. KNOWN STRUCTURES INTERPRETED FROM SEISMIC DATA

The following are images show the details of individual reflectors that may be associated with known structures previously identified in the geological model of the investigated area.

Figure 57. Details for reflector 1, corresponding to brittle fracture zone DSM-BFZ002.

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Figure 58. Details for reflector 2, corresponding to brittle fracture zone DSM-BFZ004.

Figure 59. Details for reflector 3, corresponding to brittle fracture zone DSM-BFZ005a.

59

Figure 60. Details for reflector 4, corresponding to brittle fracture zone DSM-BFZ005b.

Figure 61. Details for reflector 5, corresponding to brittle fracture zone OL-BFZ045.

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61



62


Figure 67. Details for reflector 9, corresponding to long fracture LF 1.

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Documents

ONKALO 3D Tunnel Seismic Investigations, Olkiluoto 2013