1. The LINES prototypes of optical seismometers and tiltmeters :
New instruments for geophysical monitoring offhshore ?
Pascal Bernard
IPGP, France
HIGH RESOLUTION GEOPHYSICAL MONITORING IN CHALLENGING CONDITIONS
Far offshore, deep boreholes, volcanoes, mountains, landslides…
Géosciences Montpellier: J. Chery, (F. Boudin) borehole and long base tiltmeter
IPGP (Paris) – P. Bernard, A. Nercessian, C. Brunet, J. Couteau, Seismometry
ESEO (Angers) – G. Plantier, (A. Sourice), M. Feuilloy, R. Feron, control/ processing
ENS : F. Boudin, long base tiltmeter
OSE-LAAS (Toulouse) H-C Seat, M. Cattoen, opto-electronics
LSBB (Nice) - S. Gaffet - Site for underground tests

2. ANR LINES: Geosciences Montpellier, LAAS-OSE Toulouse, EOST, IPGP
Borehole tiltmeter
L=1 m
Long Base tiltmeter
L=150 m
Seismometer
Geophone 2 Hz
= 1308 nm
mirror
Mobile target
Laser fiber
collimateur
Fabry-Pérot cavity  : Interference of the 2 reflected beams

3. Optical interferometry for measuring displacement
Reaches the best accuracies of commercial instruments (<0.1-1 nm),
with the advantages
+ the optical fiber between mechanical sensor and optical system can be several km long
+ better stability with time (no electronic drift at the sensor)
+ long fiber insensitive to EM perturbations (lightning, telluric currents, industrial environment, high voltage power lines…)
+ small size mechanical sensor
+ sensor less sensitive to high temperature (no electronic component)
+ sensor simple, robust, and unexpensive
Application for natural hazard real time monitoring in difficult environment:
far offshore, deep borehole, mountain/volcanoes,…

4. LINES project at LSBB, France
Since 2012
3 prototypes at
Laboratoire Souterrain à Bas Bruit de Rustrel
(LSBB)
1 seismometer
1 borehole tiltmeter
1 long base hydrostatic titlmeter

5. Principle of the instrument: Fabry Perot interferometry
+ phase analysis of two reflected beams in quadrature /2
Current generation and modulation + laser diod + fiber + optomechanical sensor + fiber + photodiod + demodulation + real-time calculation of target displacement on computer

6. OPTICAL SEISMOMETER :
ORIGINAL DESIGN AND PERFORMANCE

7. Geophone Sercel Horizontal 2 Hz
+ 3 km optic fiber at LSBB

8. N displacement (m) for the Sumatra M=8.7 earthquake at LSBB
30 minutes , frequency 0.01 – 3 Hz
STS2
GAS
STS2
SISMO-LINES
LASER SEISMOMETER
3 km long fiber
Geophone 2 Hz

9. 10 s 1 m N displacement (m) for the Sumatra M=8.7 earthquake at LSBB
50 seconds, frequency 0.1 – 10 Hz
GAS – STS2 VBB seismometer
SISMO-LINES – 2 Hz geophone - 3 km fiber
10 s
1 m
STS2
GAS
LASER SEISMOMETER
3 km long fiber
Geophone 2 Hz

10. N displacement (m) for the Sumatra M=8.7 earthquake at LSBB
STS2
GAS
LASER SEISMOMETER

13. Opto-electronic control WIFI
Offshore test « Sea Test Base » Lanveoc, ISEN, France
→ spring 2018 PC
internet
Opto-electronic control
Seismometer LINES
3 component
Geophones Sercel 2 Hz
+1 comp. 10 Hz
+1 « zero displ. »
WIFI
Sismo
LINES
optical cable
OBS
GURALP
Seismometer
500 m
9 m

14. OPTICAL LONG BASE TILTMETER
PRESENT DESIGN AND PERFORMANCE

15. Maturation industrial program with the SATTs AxLR et TTT (2014-2018)
Laser Control PC
3 prototypes
One sensor of 150 m length for the CERN
2 sensors for the TIGF compagny (reservoir Lussagnet) on 150x150m
150 m
Déport par fibre optique sur 300 m 15

16. No-contact measurement with the new HLS longue base
for the CERN laboratory
Fogale
voie1 CERN
150 m
First TIDES Observation

17. Noise analysis 10-7 rad GPS measurement
Power spectral density, Comparison of ILB with other sensor Fogale (Capacitive), GPS and Lily (bubble/resisitivity) Borehole tiltmeter
GPS measurement
10-7 rad
15 months recording
ILB 140 m Fogale capacitive sensor used by the CERN
ILB 150 m used in LSBB site
borehole tiltmeter (example LILY)
GPS measurement

18. LONG BASE OPTICAL TILTMETER:
2 POSSIBLE DESIGNS
In construction at ENS
To be tested offshore in Lesser Antilles in spring 2019
on a 5 km optical cable
P2(t)
P1(t)
t

19. Offshore applications :
optical cable only, with
seismometers,
pressiometers, tiltmeters,...
land
sea
Comparison of ILB LINES and LVDT results (from Earth tide measurements)
power
control
up to 40 km 19 19 19

20. - OPTICAL SEISMOMETER : present : - 2 Hz geophone (needs leveling)
- power 100 W
- fiber 10 km
future :
- 10 Hz oscillator, miniaturize < 4 cm, omnitilt
- offshore
- power < 10W
- fiber 50 km ?
OPTICAL LONG BASE TILTMETER
Present :
- measure of water level
- installation in tunnels
- power 100 W
Future  :
- measure of membrane deformation
- installation in horizontal borehole
- installation offshore
- low power
Other optical instruments :
accelerometers, broad band seismometers, pressiometers, acoustic sensors... -

21. Comparison of ILB LINES and LVDT results (from Earth tide measurements)21 21 21

22. Comparison between optical and LVDT measurement
Hydrological
loading
Hydrological
unloading
Hydrological
loading
Cumulative rain in surface
40 nanorad/month

23. M =7.1, Mexico Earthquake

24. HIPERSIS PROJECT – 2017-2018 – IPGP-ESEO – ANR, France
NEW OPTICAL SEISMOMETER
TARGET DESIGN AND PERFORMANCE
Sensor :
Miniaturization : < 4 cm :
- boreholes, antennas
- omnitilt
- more robust
- resonance 2Hz-> 10 Hz
Control/recording system :
integration, low power, low cost

26. Rennes Earthquake M=3.9 2017-09-28 9 Optical pendulum CMG40
Optical pendulum
CMG40
L22, optical
2 Hz
GAC, optical
10 Hz
TRILIUM 120

28. OFFSHORE OPTICAL PRESSIOMETER
Differential pressure between two cavities
separated by a deformable membrane
Nominal sensitivity of the membrane:
d=1 m for 0.1 mm water P
i.e.,
d=1 nm for = and L=100 m
Membrane wafer sil-tronix 0.2 mm

29. ANR « HIPERSIS »
sismo optique 10 Hz – 4 cm – omnitilt
Developpement algorithmes
FUI « MIRZA »
Calibration pendule optique ; inclinomètre optique de forage hrizontal;acquisition intégrée faible consommation
SATT-OUEST « SISMO-MARIN » : printemps 2018
Installation au Sea Test Base du sismo optique 4 comp (3x2 Hz + 1 x 10Hz)
500 m de cable, 8 m de profondeur
Intégration contrôles/processing
EU INTERREG  CARAÏBE  « PREST » : printemps 2019
Installation aux Saintes du sismo optique 4 comp
+ 2 pressiomètres optiques + 1 inclinomètre longue base optique
4 km de cable, 30 m de profondeur
Cibles envisagées de capteur optique sismo et géodésie offshore, en discussion :
Chili : subduction - Iquique / Valparaiso
Antilles : subduction – Guadeloupe/Martinique
Grèce : Golfe de Patras
Naples : baie de Pozzuoli
Marmara ?

30. Measurement from ILB LINES
Difference between LVD Tand ILB LINES measurements
Comparison of ILB LINES and LVDT results (from Earth tide measurements) 30 30 30