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Catherine Berge-Thierry * , J.F. Fels, P. Dervin, P. Guéguen,

THE FRENCH PERMANENT ACCELEROMETRIC NETWORK: TECHNOLOGICAL AND PARAMETRICAL CHOICES SCIENTIFIC GOALS AND RESULTS. Catherine Berge-Thierry * , J.F. Fels, P. Dervin, P. Guéguen, S. Nechtschein, D. Hatzfeld, P. Volant, P.Y. Bard, F. Courboulex, P. Dominique, B. Feignier

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Catherine Berge-Thierry * , J.F. Fels, P. Dervin, P. Guéguen,

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  1. THE FRENCH PERMANENT ACCELEROMETRIC NETWORK:TECHNOLOGICAL AND PARAMETRICAL CHOICESSCIENTIFIC GOALS AND RESULTS Catherine Berge-Thierry*, J.F. Fels, P. Dervin, P. Guéguen, S. Nechtschein, D. Hatzfeld, P. Volant, P.Y. Bard, F. Courboulex, P. Dominique, B. Feignier * Institut de Radioprotection et de Sûreté Nucléaire/berssin catherine.berge@irsn.fr http://www-rap.obs.ujf-grenoble.fr C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 1

  2. Technicians and scientists that ensure the maintenance and improvment of the network: • Institut de Physique du Globe de Paris (West Indies), • Laboratoire de Géophysique Interne et de Tectonophysique, • Laboratoire des Ponts et Chaussées, • Institut de Radioprotection et de Sûreté Nucléaire, • Géosciences-Azur, le Bureau de Recherches Géologiques et Minières, • Ecole et Observatoire des Sciences de la Terre de Strasbourg, • Commissariat à l’Energie Atomique, • Observatoire Midi Pyrénées, • Centre d’Etudes Techniques de l’Equipement, • Conseil Général de la Martinique, • Ministère de l’Environnement et du Développement Durable, • Direction de la Recherche et des Affaires Scientifiques et Techniques, • Institut National des Sciences de l’Univers • Université de Bretagne Occidentale • Université de Clermont Ferrand C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 2

  3. Strong motion stations in the 80’s: ~ the NPP map • 0.01g threshold • Analog instruments • (SMA1, SMA2essentially) • Very few events detected • not sensitive enough • inadequacy for a SM • database construction C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 3

  4. Birth of the French Accelerometric Network • Aims of the Network: • Provide accurate data for scientists and engineers • Sensitive threshold, without saturation for strong motion • Instruments developed by a French company Testing phase in most of the seismic areas in France (metropolitan): • Nice, Grenoble, Alps instrumented, • Emphasized significant site effects in sedimentary valleys (Grenoble) • Demonstrated the feasability and accuracy of instruments The Ministry decided sponsoring the RAP, with an objective of 100 stations C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 4

  5. 91 « RAP » stations installed in 2003 Number of stations from 1995 up to 2002 C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 5

  6. RAP Network = RAP stations + Associated SM stations IRSN, BRGM, LDG and Martinique General Council (metropolitan and French West indies) Instrumentation and record processing ≠ RAP stations C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 6

  7. RAP strong motion Database, end of 2003 Evolution of recorded events Evolution of records 2557 seismic events 4510 3 component records C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 7

  8. Weight/dimension: 4 Kg, 260 x 160 x 120 Power requirements: 11.5 – 18 Volt, 2.5 Watt Input voltage full scale +/- 5 Volt +/- 1g Input impedance: 25 Kohm Digitizers: Crystal CS5321+CS5322, sigma-delta, 24 bits. Overall digital noise: 8 counts p-to-p. System clock stability: 5 10-7 External time reference: DCF radio receiver. Data time stamp: internal time + external time. Data storage: trigger records saved on internal 8 Mb Flash memory Communication: serial RS232, to modem or PC RAP station: instrumentation and data processing • Sensors: Kinemetrics (Episensor T), Guralp, • Acquisition system: Titan developed by Agecodagis C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 8

  9. Time constant for LTA 30 s Time constant for STA 1 s Triggering threshold 4 or 6 depending on site Pre-event 10 s Trigger record minimum duration 30 s Trigger record maximum duration 100 s • Trigger mode (STA/LTA) • Sampling: 125 sps • FIR filters (time delays removed during processing) • « Titan » format (serial type) • Data stored on a 8 Mb Flash Memory memory is full within 4 ou 5 days (~ 50 records) Operations performed « on site » (regional RAP center) C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 9

  10. RAP Central Site FTP servers Regional Centers Seismic catalogues Interogating stations & retrieving records Regional Center Maintain stations RAP Central Site Offset Removal (SAC) Storage, checking- validation Distribution through the RAP WEB site C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 10

  11. Durance Tricastin Grenoble The IRSN – Associated Network The Moyenne Durance Fault Network: Velocimetry + Accelerometry C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 11

  12. Sampling 200 sps Internal FBA23 Characteristic frequency: 50Hz, damping 70%, dynamic >135dB from 0.01 to 50hz Frequency range usable for data 40% of the sampling using digital anti-aliasing filters, ie [0 to 80Hz] for 200 sps. Internal Episensor  Frequency range 0 to 200Hz, dynamic >145dB Final anti aliasing filter no causal, linear response for the phase, pure delay Triggering with a threshold 0.5 to 1mg depending on the stations Filter linked to the trigger IIR Bandpass filter : classic strong [0.1Hz-12.5Hz] with 200sps IRSN stations acquisition parameters K2/Etnas (kinemetrics) C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 12

  13. IRSN strong motion data processing StandardKinemetrics method : Strong Motion Analysis for computing corrected accelerograms V2 format • Opening of the event file recorded by a K2 or Etna acquisition system (.EVT), • Writing IRSN raw data in CDMG format (V1 File) • Removing the continuous component (offset evaluated on the entire event file), • Instrumental correction • Integrating (including a high pass filter) velocity and displacement time series • Writing IRSN corrected data in CDMG format (V2 File). C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 13

  14. 1st decimation factor  (instrumental correction) [1]keeping the maximum number of samples for corrected data Half length of filter operator: low pass filter for offset correction, [10] Acceleration decimation factor: high pass filter of acceleration during the offset correction, [10] Velocity decimation factor: high pass filter of velocity for the high-pass filter step, [10] Displacement decimation factor: high pass filter of displacement for the high-pass filter step, [10] Terminal frequency: final frequency of the Ormsby low pass filter (instrumental correction) [50] Roll-off width: width of the Ormsby low pass filter (instrumental correction) [3] Corner frequency : corner frequency for Ormsby high pass filter (offset correction and high pass filtering of velocity and displacement) [0.25] Roll-off width - Ormsby high pass filter - (offset correction and high pass filtering of velocity and displacement) [0.1] IRSN strong motion data processing IRSN processing: TRIFUNAC Branch • Storage in the database • Distribution via • RAP WEB site RAP Central Site Corrected IRSN data (under RAP format) C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 14

  15. 3 other associated networks maintained by: - BRGM (16 in French West Indies) - LDG (2) - Martinique General Council (28) Geosig instruments (processing not described in this contribution) C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 15

  16. RAP « weak motion » records Significant amplifications (duration, amplitude) in sedimentary valleys C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 16

  17. The Mw=5,1 « Besançon » event (23/02/2004)recorded by RAP Network • compute Moment magnitude, • compare recorded acceleration with predicted one, C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 17

  18. Conclusions • Until the 90’s strong motion recorded associated to detection • (NPP site safety) • French Accelerometric Network: scientific and engineering aims • - beginning of structural instrumentation, • - improvement of geological site characterization • Moderate Metropolitan Seismicity conducted the choice of low • threshold for RAP stations (trade-off): • - this strategy allows the recording of weak motion (site effects) • necessity to increase the Flash memory to avoid any loss of data • in case of communication failures (aftershocks) • Federation of the scientific and user communities to improve • the network and the data distribution C. Berge-Thierry et al., 26- 27 May 2004, Strong Motion Record Processing 18

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