Eighty percent of GEOSCOPE stations are still equipped with STS-1 sensors (Figure S1). Because STS-1 is no longer manufactured by Streckeisen, replacing malfunctioning sensors is no longer possible, which leads us to fix them ourselves whenever possible or to install STS-2 sensors instead. STS-2 sensors are known to present higher noise at long periods and require particular conditions during their installation (Hanka 2000). Some island stations or stations close to the coast such as AIS, HDC, FDF, FOMA, MPG, and MBO are equipped with STS-2 seismometers, as are stations operated by GSN (TRIS), CEA/DASE (DZM, TAOE), or CTBTO (ATD). A few stations are equipped with both a vertical STS-1 and a three-component STS-2 (AIS, TRIS) as seen in Table 1 (main text). Our station instruments have a constant response in velocity between 360 s and 10 Hz in the case of an STS-1, and between 120 s and 10 Hz in the case of an STS-2. The details of the recorded channels are listed below.
| Channel | SEED Name | Unit | Flat Response | Sampling Rate | Number of Bits |
|---|---|---|---|---|---|
| Very Long Period | VH | m/s | 360s*–20s | 0.1 sps | 24 or 26 |
| Long Period | LH | m/s | 360s*–2s | 1 sps | 24 or 26 |
| Very Broadband | BH | m/s | 360s*–10Hz | 20 sps | 21 or 24 |
| Mass Position | LM | m/s2 | 0s–10Hz | 1 sps | 16 |
| Temperature | LKI | °C | 1 sps | 16 | |
| Pressure | LDI | Pa | 1 sps | 16 |
The upgraded stations are all equipped with Quanterra type ADC converters, Q4120 series (Q4126-6 channels or Q4128-8 channels) or Q330 series (Q330-6 or Q330-HR).
The stations have been progressively set up with pressure sensors (Streckeisen, Vaisala, or Effa-Druck microbarometers) and handmade thermometers. At the end of 2009, 16 stations were equipped with micro-barometers and nine stations with micro-thermometers (Figure 8B, main text). A systematic installation of environmental sensors enables us to quantify the influence of the environment on seismic noise and to reduce the noise level of seismic data, especially at very long periods.
Many manuals exist regarding the installation of broadband seismometers (Holcomb and Hutt 1992; UCB 1997; Urhammer et al. 1998; Bormann 2002; Widmer-Schnidrig and Kurrle 2006). STS-1 seismometers of the GEOSCOPE network are protected against unfavorable environmental conditions such as wind, high diurnal or seasonal variations of temperature and atmospheric pressure, variations of the magnetic field, corrosion due to humidity, and possible flooding. First, they are enclosed inside metal boxes. Second, they are protected by hermetic glass bells, under partial vacuum, to avoid noise due to atmospheric pressure variations. In some stations, the glass bell is filled with fine Styrofoam seeds. The insulating boxes include internal fresh desiccant and external heat-reflecting blankets. Electric signals are fed through a hermetic plug. Very often, the ceramic plates supporting the seismometers are carefully cemented to the floor. In other cases, these plates are put down on a sand bed, held back by a rigid frame. Barometric variations may cause tilt noise on the ground but not on the ceramic plate. The vertical sensors are always under a vacuum; the quality of the vacuum is checked by adjusting the POS signal. The horizontal components are not always under a vacuum; some stations exhibit a lower noise level without a vacuum inside the glass bells.
Different techniques have been applied to orient the horizontal sensors, such as geodetic gyroscope or magnetic compass measurements or solar sighting. At some stations, it was necessary to use a geodetic gyroscope, for example in long tunnels or deep vaults. Precise orientation of the sensors, when available, was carefully marked on the floor or the pillar.
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The GEOSCOPE team has continuously evolved during the past 25 years. When dedicated scientists, engineers, and technicians have retired, new generations have taken over, fostering the development of new tools to respond to the scientific challenges of their time. Currently, the staff working at IPGP and EOST leads the GEOSCOPE team. They are supported by the groups working at CEA/DASE, IPEV, and IRD.
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Gérard Ball, Sylvie Barbier, Eric Basier, Pascal Bernard, Françoise Besset, Michèle Bitterly, Sébastien Bonaimé, Jean Borsenberger, Jean-Marc Brendlé, Jean-Michel Cantin, Michèle Caillard, Jean-Michel Cantin, Hugues Castarède, Chantal Condis, Pascal Dayre, Aymeric de Carfort, Anne-Sylvie de Bièvre, Anne Deschamps, Christiane Desfoux, Bernard Dole, Vincent Douet, Jean-François Fels, Danielle Fouassier, Florence Giangrande, Nicole Gillet, Gwénola Guiveneux, Saphira Hounsihoue, Jean-François Karczewski, Jean-Claude Koenig, Jean-Claude Lépine, Nicolas Leroy, Jean-Jacques Lévêque, Denise Lévy, Robert Longeon, Anne-Marie Margotteau, Jeannine Moncouilloux, Michel Morand, Alfred Müller, François Paillous, Constanza Pardo, Geneviève Patau, Sandrine Pelletier, Frédérick Pesqueira, Nicole Pomarel, Annick Pyrolley, Marie-Christine Roche, Olivier Rozier, Jean Savary, Jean-Marie Saurel, Eugène Speisser, Daniel Streng, Jean-Yves Thoré, Jeannot Trampert, and Anne Wermelinger.
It is difficult to name everybody, but we would like to thank all the researchers, engineers, and technicians who have worked and are still working with us in France or in their respective countries, including:
Anis Abdallah, Vitaly Adushkin, Tim Ahern, Nourredine Akacem, Nelson Allende, Donald Anderson, Kent Anderson, Olivier Andrieu, Sok Appadu, Carlos Aranda, Marcelo Assumpcao, Luciana Astiz, Catherine Baldassari, Sergio Barrientos, Sarah Bazin, Hadj Benhallou, Abdelhamid Bendekken, Jonathan Berger, Rosa Bernal, Jesus Berrocal, Mourad Bezzegoud, Mike Blackford, Rémy Bossu, Jacques Bouchez, Jacques Boulesgue, Boris Bukchin, Ray Buland, Rhett Butler, Jean-Philippe Caminade, Jaime Campos, Yves Cansi, Yves Caristan, Claude Cavoit, David Novello Casanova, Philippe Catherine, Eric Clévédé, Jean-Claude Delmond, Roger Decourt, John Derr, Jean-Michel Devaux, V.P. Dimri, Chuck Doll, Bernard Dost, Vincent Douet, Balraj Dunputh, Alexei Egorkin, Bruno Feignier, Célia Fernandez, Roger Foy, Yoshio Fukao, Germinal Gabalda, Luis Gailhardo, Christian Garita, Michel Gissang, Alejandro Gonzalez, Dimitri Gounbin, Larissa Gounbina, Fembe Goutbeek, Philippe Guerendel, Cyril Guinet, Winfried Hanka, Alain Hauser, Andres Heinloo, Mohamed Hfaiedh, Gary Holcomb, Jean-Marie Holl, Robert Hutt, Mohammed Jalludin, Gilbert Juste, Sophie Jymmikone, Brian Kennett, Valentin Kovalev, Vladimir Kulikov, Ogie Kuraica, V.N. Kovaliov, Philippe Kowalski, Carène Larmat, Jean-Louis Laurent, Frédéric Lauret, Thorne Lay, David Lazo, Pierre Lebellegard, Jean-Jacques Lévêque, Anatoli Levshin, Philippe Lognonné, Marc Lointier, Rémy Louat, Raul Madariaga, Karen Mac Nally, Bernard Massinon, Luis Mendes Victor, Yves Ménéchal, Lucien Mollard, Frédéric Moreau, M. Morfin, Eli Morris, Philippe Morisset, Nicolas Moutou, Abdou Salam Ndiath, David Nakedau, Alex Nercessian, Ann Ngo, Caryl Peterson, Jean-Louis Plantet, Kusalya Surya Prakacham, Marino Protti, Herb Mac Queen, Luis Quintanar, Vijaya Raghavan, Andry Ramanantsoa, Gérard Rambolamanana, Ramakrishna Rao, Marc Régnier, Dominique Reymond, Jean Roques, Yang Zhi Rong, Olivier Roult, Gérard Ruzié, Daniel Sampson, Jean-Marie Saurel, William Schillinger, François Schindele, Nikolaï Shapiro, David Simpson, Krishna Singh, Annie Souriau, Spiro Spiliopoulos, Oleg Starovoit, Joseph Steim, Sandy Stromme, Gerardo Suarez, Chad Trabant, Torild Van Eck, Isao Yamada, Abdelkrim Yelles-Chaouch, Jean-Pierre Viodé, Ruoping Wei, Boming Zhang, and the annual scientific and technical teams maintaining the stations of the South Indian Ocean and Antarctica in TAAF territories.
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Bormann, P., ed. (2002). IASPEI New Manual of Seismological Observatory Practice. Potsdam, Germany: GeoForschungsZentrum Potsdam, ISBN 3-9808780-0-7.
Holcomb, L. G., and C. R. Hutt (1992). An Evaluation of Installation Methods for STS-1 Seismometers. USGS Open File Report 92-302.
Hanka, W. (2000). Which parameters influence the very long period performance of a seismological station? Examples from the GEOFON network; http://www.gfz-potsdam.de/geofon/manual.
UCB Seismological Laboratory at Berkeley (1997). Guidelines for installing broadband seismic instrumentation; http://www.seismo.berkeley.edu/seismo/bdsn/instrumentation/guidelines.html .
Urhammer, R. A., W. Karavas, and B. Romanowicz (1998). Broadband seismic station installation guidelines. Seismological Research Letters 69, 15–26.
Widmer-Schnidrig, R., and D. Kurrle (2006). Evaluation of installation methods for Streckeisen STS-2 seismometers, http://www.geophys.uni-stuttgart.de/~widmer.
Wielandt, E., and G. Streckeisen (1982). The leaf-spring seismometer: Design and performance. Bulletin of the Seismological Society of America 72, 2,349–2,368.
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Figure S1. FDSN and GEOSCOPE networks in 2000, with indication of sensors at GEOSCOPE stations (80% of stations equipped with STS-1 sensors and 20% of stations equipped with STS-2 sensors).
Figure S3. GEOSCOPE data from 1982 to 2009
Figure S5. Distribution of the GEOSCOPE stations in 2000 with indication of the state of the art at that time. Remotely accessible stations corresponded to a phone line transmission, for large events only (Ms > 6.5).
Figure S6. Real-time link between the RER station (La Réunion Island) to the GEOSCOPE Data Center in Paris. More than 3 km of optic fiber has been deployed to conduct the signal outside the tunnel. Then, an ethernet bridge loads the signal to the roof of the St. Benoit College, where ADSL is operating.
Figure S7. All large earthquakes of year 2009 for which source mechanism parameters have been determined by Clévédé and Patau (2009, personal communication). See also http://geoscope.ipgp.fr.
Figure S8. The CNATOI (Centre National d’Alerte aux Tsunamis dans l’Océan Indien/National Center of Tsunami Warning in the Indian Ocean) initiated the upgrade of the six existing GEOSCOPE stations located in the Indian Ocean (AIS, ATD, CAN, CRZF, DRV, PAF, RER) where possible satellite data transmission was available, as well as the installation of two new sites (MAD/FOMA and ROD. At present: data is stored at the GEOSCOPE Data Center in Paris and can be fetched by all operational tsunami warning centers around the world, such as PTWC, JMA, GITEWS, ATWS, etc. In the future, data are planned to be sent to a unique local warning center.
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