The French National Network of Seismic Survey (RéNaSS)
The French metropolitan territory is an area of moderate seismic
activity compared to the Euro-Mediterranean domain. However,
based on a historical catalogue and one century of instrumental
records the possibility that a major earthquake occurs
on the French motherland should be considered. During the
previous century, the earthquake which occurred at Lambesc
(1909, I0=IX) is the most significant. The recent
earthquakes in the Pyrenees (18/02/96, M=5.2) and in the Alps
(15/07/96, M=4.9) remind us that large and destructive events
could happen in France. Real-time monitoring of the French
seismic activity is the main task of the National Network of
Seismic Survey (
EOST-IPGS, 5 rue René Descartes, F-67084 Strasbourg Cedex
The National Institute of the Science of the Universe
supports since the middle of the seventies a national program to
survey the seismicity of France. Nowadays, RéNaSS gathers
all the regional seismic networks and isolated
seismological stations installed and maintained by the
Observatories of the Science of the Universe (OSU), the
Institute of Physics of the Earth of
Paris and the seismological laboratories
of different universities. The two objectives of RéNaSS are:
Born from the necessity to organise and improve the
instrumental seismic coverage of France at the beginning of
the eighties, RéNaSS is a federation of regional seismic
networks and broad-band seismological stations whose main
components are linked at a central site located in
Strasbourg. The current organisation is as follows:
- A real-time monitoring of the French seismicity including
the distribution as a 'routine service' or as a 'rapid
determination service' of earthquake parameters. This
activity is labelled as a 'public service' mission by the Home
Office and implies a 24h duty.
- To record, collect, archive and distribute the seismic data
(seismograms of local and teleseismic events and earthquakes
parameters) for scientific purposes.
Nowadays, RéNaSS consists of:
- The national headquarters of RéNaSS is in charge of
the rapid determination of earthquake parameters on a 24h schedule, the
collection, the archiving and the distribution of seismograms,
arrival times and source parameters.
- The regional headquarters have the technical and scientific
responsibility of the regional seismic network. They are also the
main partners of local and regional administrative councils.
We distinguish between real-time networks (which directly
contribute to the rapid determination service) and the networks
for which the seismological data are collected afterwards by
either the regional or national centers.
- A short-period university network consisting of 103
seismological stations distributed over 7 regional networks and some
independent stations. These regional dense seismic networks are
located in areas where the historical
and instrumental seismic activity are the most important, thus
allowing both a low triggering threshold and a very precise
location of earthquakes.
- A broad-band network equipped with a high dynamic acquisition
system (Figure 1).
- A central site which is in charge of the real-time monitoring
of the seismic activity and of the routine processing of the
short-period and broad-band networks.
'Real-time' short-period regional seismic networks
The real-time short-period networks are the Rhine Graben network (9 1comp
stations), the Nice hinterland area network (5 1comp and 2 3comp
stations), the Provence network (8 1comp stations) and the region of
Massif Central network (4 1comp and 3 3comp stations). The transmission
of seismological data is achieved using radio-telemetry from the
remote station in the field to a central station equipped with a
continuous data recording system. A PC Linux-based data
acquisition system installed by the central site of RéNaSS
normally complements a regional recording system.
Such a PC-based recording system enables one to look at the seismic
noise in real-time through the Internet simultaneously at
Strasbourg and at the regional headquarters. Upon a detection,
the seismograms and the automatic phase pickings are
automatically transmitted to Strasbourg using the Internet again.
The national broad-band network is currently composed of fourteen
stations equipped with Streckeisen STS2 sensors and two
equipped with Streckeisen STS1 sensors (Figure 1):
There are three regional networks off-line or in near real-time:
the Pyrenean network composed of 20 isolated stations (15 3comp and
5 1comp), the region of Alps network (so-called 'Sismalp') composed
of 44 stations (9 3comp and 34 1comp) and the region of Charentes
network composed of 5 stations (1 3comp).
The data are transmitted to the regional center or to the central
site at Strasbourg using either switched phone links or the
METEOSAT satellite (5 Pyrenean stations). The connections
between the central site and these regional centers is described
later on. Three additional autonomous stations are operated:
Mencas, Dompierre and Brest. These independent stations are
connected with the central site at Strasbourg through a PC-PC link
on a switched phone network.
The stations of Arbois, Calern, Chute-du-Sampolo and
St-Étienne-de-Tinée are under the responsibility of
the university of Nice Sophia-Antipolis (TGRS-RéNaSS network). The stations of
Argentières-La-Bessée, Digne, Grand-Maison and Sixt
are under the responsibility of the Observatory of Grenoble
The remaining sites are directly operated by the national
headquarters at Strasbourg.
- STS 1: Saint-Sauveur-de-Badole (SSB) and Echery (ECH) belonging
to the Geoscope global network.
- STS 2: Arbois (ARBF), Argentières-La-Bessée
(OGAG), Calern (CALN), Chizé (CHIF), Chute-du-Sampolo
(SMPL), Clermont-Ferrand (CFF), Digne (OGDI), Dourbes (DOU,
Belgium), Grand-Maison (OGGM), Arette (ATE), Rennes (RENF),
Saorge (SAOF), St-Étienne-de-Tinée (STET) and
The stations equipped with STS2 sensors are endowed with an
acquisition system called TITAN-ATLAS developed by the
They have been designed by the manufacturer on the basis of a
'request book' issued jointly by the seismologists responsible
for different seismic survey networks. The data are continuously
recorded on a ring buffer of 2 Gb (4 Gb in the near future). It
is possible to record up to 6 channels with a sigma-delta
A/D converter having a 24 bits dynamic range.
The connection with central or regional hubs is made
through switched phone lines.
Figure 1. Location of broad-band stations on the French metropolitan territory.
The national headquarters at Strasbourg are responsible for the
daily exploitation of the 69 stations linked to Strasbourg.
Approximately 2500 local earthquakes per year are processed.
The parametric data are distributed on a daily and a weekly
basis both as classical paper bulletins and electronic
reports through the Internet. The flow chart of the general
operations at the national center is shown in Figure 2. At
Strasbourg, raw data (seismograms) and parameter data (phase
pickings, earthquake location and magnitude) are immediately
accessible on the RéNaSS website.
Figure 2. Synoptic scheme of the data processing at the national headquarters.
The seismic duties of RéNaSS consist of a routine survey
of the national and worldwide seismicity from seismic signals
(seismograms) collected through the regional seismic networks and
isolated stations using different transmission links
(radio-telemetry, switched or dedicated phone lines, Internet,
satellite). These duties also include the distribution of obtained
earthquake parameters and the archiving and distribution of the
raw data, the phase picking and the hypocenter parameters.
Seismograms are continuously analysed and phases picked
automatically. When several phase pickings become available,
an initial location of the event is obtained using an algorithm
depending on the 'probable' nature of the earthquake
(local, regional, teleseismic). The estimated location and magnitude
are compared with globaly obtained event detections and, if appropriate,
an alarm is declared.
In case of such an alarm, the seismologist on duty comes
to the data center and collects all the available information from
other seismic networks or agencies - the national headquarters
at Strasbourg are in permanent connection through the Internet with
other national or international seismological institutions - .
An improved location is obtained and within 60 minutes after the
earthquake occurred its parameters are made publicaly available.
In other cases, the events are routinely processed each morning.
Data are then stored in the data base where they are
made available through a website for either scientific purposes or general
public information and a monthly bulletin is published.
The national headquarters of RéNaSS is also responsible
for the fast determination of large events, and has to
inform the civil authorities when an earthquake has been felt.
This kind of activity of fast determination requires
scientists on duty, 24 hours per day and seven days per week.
The scientific applications of the short-period regional seismic
networks concern mainly studies on seismic tomography and
seismotectonics including some local studies on the instrumental
seismicity and the seismic hazard. With seismic tomography,
very new results were obtained for deep structure investigations
in the Pyrenees, Alps, Rhine Graben and the Armorican Massif.
Additional studies on seismic anisotropy at a regional scale or
local scale provide new results on deformation at depth
related with recent or old orogenies. A main contribution to
seismotectonics based on data obtained by these regional networks
is the new seismotectonic zoning map. Papers based on focal mechanisms
are regularly published.
Publications on the two large earthquakes which occurred
recently in France address the seismogenesis processes acting in
The scientific output of broad-band data concerns mainly source
studies and new structural models of Europe.
At the central headquarters at Strasbourg we are presently developing
automatic procedures to retrieve moment tensors of large earthquakes
within near-real time and well in advance of any field actions:
On a long-term, the calculation of new structural models and the
constitution of a data base of focal mechanisms and centroid
moment tensors of moderate to large earthquakes - similar of
what is currently existing at a worldwide scale -
would largely contribute to a better knowledge of regional
tectonics and seismic hazard in France.
A list of publications to date is available.
RéNaSS is an operating network for the real-time seismic
surveillance of France as well as for its scientific activity.
Its federal structure allows a strong regional presence. In
addition, its 'university' label has a great impact towards the
general public and the media. Its main forces are:
- The seismic moment of all earthquakes having a magnitude
M>4 and located in France or its immediate surroundings.
- The seismic moment and the focal mechanism for all
earthquakes located in the same area with a magnitude M>4.5.
- A continuous link with the general public and a systematic
educational information by a seismologist in case of destructive earthquakes.
- Continuous upgrade of the information in case of a seismic crisis.
- On site intervention in case of a major earthquake.
- A positive scientific output of the data.
RéNaSS is constantly improving its professionalism, which
implies to work on a better homogeneity of all used instrumental
equipment and a greater strictness in collecting and archiving
the seismic data on a long-term basis, which, at the end, is the
main and primary mission of seismological observatories. Among
the future objectives, a better instrumental coverage of the
territory and a more user-friendly and complete access to all
possible 'earthquake' information are on the top of the list.
Concerning the instrumental covering RéNaSS
will be instrumentally and technically improved by:
Concerning the dispatching of the earthquake information,
both the regional and national headquarters will act on:
- The addition of a four stations network located in the region
- The progressive and systematic replacement of 1 component by
3 components seismometers; in addition, some networks will be
equipped with long period sensors.
- Upgrading and securing the computer-based fast determination.
- The use of satellite for data transmission: the fast
development of satellite technology with reduced costs compared
to the rapidly increasing technical, administrative and financial
difficulties to maintain radio-telemetry transmissions which motivate
a transition to new technologies.
RéNaSS will not exist without a strong, positive and
unfailing support by INSU (CNRS) since the idea was born at the
beginning of the eighties. The Ministry of Education, Research
and Technology (MENRT) contributes significantly to the
development of this Observatory task. Seismic surveillance would
not be possible without the following Observatories of the
Science of Universe: Clermont-Ferrand, Grenoble, Paris, Toulouse,
Strasbourg. Different universities contribute to maintain this
activity through a strong staff support:
Marseille St-Jérôme (UMSJ), Nice Sophia-Antipolis
(UNSA) and La Rochelle (ULR). Many scientists, engineers,
technicians, students have been and are currently involved in
RéNaSS. Without their contribution, nothing would have
- The data base access from a large set of services.
- The improvement of the distribution tools: GIS and voice server.
Table 1. List and coordinates of broad-band stations.
||Clermont Ferrand (63)
||09/1995 (closed 10/1998)
||Station of Geoscope
||Station of Geoscope