Seismic section
Introduction
The Ebre Observatory was founded by the Society of Jesus in 1904 at the town of Roquetes (northeastern Iberian peninsula). Its geographical coordinates are: 40°49.23N and 0°29.60E. Although since the establishment of the Observatory it was devoted to the study of Solar-Terrestrial physics, a seismological section was created, because at that time it was believed that there could exist a relation between solar activity and seismicity. It is, so, the oldest seismic station in Catalonia and the third in Spain after San Fernando (1898) and Cartuja (1902) both located in the southern part of the Iberian peninsula.
Research lines
- Propagation and attenuation of seismic waves.
- Seismic ambient noise analysis
- Regional seismicity: characteristics, distribution and focal mechanisms.
- Historical seismometry. Reutilization of instrumental data.
- Determination and callibration of magnitude laws.
Instrumentation
The old seismographs
(1904-1913) - The first instruments installed were, on the one hand, a Grablovitz seismograph, with a rather long period, which was very useful for detecting teleseisms. On the other hand, a short period Vicentini microseismograph recording the three components was also operating, which was suitable for recording regional earthquakes. These instruments were purchased directly to Professor Grablovitz in Ischia and Professor Vicentini in Padova and they recorded mechanically on smoked paper.
(1914-1941) - The seismographs of the Observatory were modernized with the installation of a Mainka type horizontal seimograph and a vertical pendulum, all of them built at the Observatory by copying the design of the widespread instruments at that time. Because of their ageing and also because of the existence of more modern instruments, the Grablovitz and Vicentini seismographs stopped working gradually. The outbreak of the spanish civil war affected the normal operation of the seismic section at the Observatory. However, the seismic recording only was interrupted for three months and restarted in July, 1938, although the working conditions were very poor.
(1942-1966) - An improvement of the instrumentation was performed by means of the construction of three new seismographs using the existing pieces of old instruments. Two horizontal Mainka type seismographs of 1500 kg and a vertical pendulum of 635 kg were built under the direction of the jesuits of the Observatory.
Summary table
| Seismograph | Component | M (kg) | To (s) | Amplification | start recording | end recording |
| Grablovitz | NE-SW NW-SE |
12 | 13 | 8 | 1904 | 1918 |
| Vicentini | Z N-S E-W |
50 100 100 |
0.85 2.3 2.3 |
150 90 90 |
1904 1904 1904 |
1936 1916 928 |
| Mainka | N-S E-W |
1501 157 |
14.8 7.8 |
175 60 |
1914 1914 |
1940 1937 |
| Vertical pendulum | NE-SW NW-SE N-S |
316 316 |
2.6 |
125 |
1914 1915 |
1915 1941 |
| Mainka-Ebre | N-S E-W |
1500 1500 |
15.4 10.8 |
275 150 |
1940 1942 |
1966 1966 |
| Vertical pendulum | N-S | 635 | 2.5 | 230 | 1943 | 1961 |
Images
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Current instrumentation
EBR Station (World Wide Standardized Seismograph Network)
In 1966, the electromagnetic seismographs with galvanometric recording started operating at the Observatory. First, three Teledyne Geotech, Benioff type, short period seismographs were installed and later, in 1968, three Sprengnether long period seismographs completed the instrumentation. In 1974 the short period photographic recording was changed to ink by means of some Lennartz electronic amplifiers. These 3 short period seismographs are still in operation. The long period recording was stopped in 2000.
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| Short period (Benioff) and long period (Sprenghnether) sensors installed at a depth of 7 meters on rock |
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| Long period galvanometric recording system |
EROQ station
In 1987 a short period, three component seismic station was installed at 8 km from the Observatory by the Instituto Geográfico Nacional. The signals of the three Kinemetrics SS-1 Ranger seismographs are sent via radio to the Observatory, were ink recording is performed. From the Observatory, seismic signals are sent to the IGN in Madrid via telephone line, where they are digitized. The data are also received via telephone by the Institut Cartogrāfic de Catalunya (ICC) in Barcelona.
Broad band stations
In 1999, a new place located at 20 km from the Observatory was chosen for the installation of a Nanometrics satellite broadband seismic station in collaboration with the IGN. A cave located in the interior of an old church was finally chosen after doing the seismic noise measurements. A Guralp CMG-3T seismometer and a Nanometrics satellite data acquisiton system are in operation at Horta de Sant Joan since 2000. The data are transmitted via satellite to the IGN in Madrid were the receiver antennas are located.
At present, EBR station is equipped with a Wielandt-Streckeisen STS-2 seismometer with a flat velocity proportional response characteristic in the frequency range 8.33 mHz to 40 Hz and a 24-Bit Quanterra Q680-LV datalogger. EBR station contributes data to the Virtual European Broadband Seismograph Network as a part of the MEREDIAN (Mediterranean-European Rapid Earthquake Data Information and Archiving Network) real-time data exchange initiative. In this sense, data streams from the SeisComP/SeedLink server are collected by the Antelope real-time system at the ORFEUS Data Centre.
 STS-2 |
 Quanterra Digitizer |