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PRSN Instrumentation

     Currently the PRSN operates 25 seismic stations in Puerto Rico, Dominican Republic and British & US Virgin Islands. There are two types of stations; analog stations which consist of a sensor, a communication system, batteries and solar panel, and other peripheral electronic equipment. And digital stations, which consist of the equipment mentioned above and also require a digitizer.

     There are three main types of sensors: Short Term, Broadband and Accelerometer. The short-period and broadband stations are also known as weak motion stations because this stations detect less intense events very well, but when the events are very strong, it may be saturated. The accelerometers are considered strong motion stations because they are designed to record in scale the events of greater intensity.

     Each short period station consists of a Teledyne Geotech S-13 vertical component seismometer, with a natural frequency of 1Hz, a Teledyne Geotech VCO pre-amplifiyer, a REPCO or Monitron radiotransmiter , modulated to a 150 MHz frequency and a 12 V battery that is recharged by solar panels on most of the stations. In early 1992 the SJG seismic station became a 3 component station, with the installation of a Mark L-43D geophone, with a natural frequency of 2Hz and 5500 ohms resistance. The Mona Island and Desecheo stations followed SJG. The broad band station in Cornelia Hill (Cabo Rojo) consists of a Guralp CMG-407 seismometer.

     There are three repeating stations: Cerro Piña in Caguas, Cerro Santa Ana in Maricao and Cerro Punta in Jayuya. In these stations the signals from the different seismic stations are combined and relayed forward by means of radion signals, except the segment betwwen Cerro Punta and Cerro Santa Ana, where the information is transmited via microwave.

     All the signals from the seismic or receiving stations are received directly in real time at the data acquisition center, located in the PRSN office in the Mayagüez Campus of the University of Puerto Rico. The reception equipment consists of antennas and REPCO radio receivers (810-055-03). A Teledyne discriminator separates all the signal, which are then amplified. The data from 8 of the stations is registered simultaneously on the seismographs. Since September, 1991 the IASPEI data acquisition system (Tottingham y Lee, 1989) started running on a PC 386 and recorded the signals of all the stations, once an eventwas detected by at least three stations. This program replaced the INTEL information system that recorded the events on magnetic tape, and was installed by the Lamont-Doherty Earth Observatory. Along with the IASPEI system, since June 1992, the SOUFRIERE developed by the Seismic Research Unit (SRU) of the University of West Indies in Trinidad, had been recording earthquakes on a separate PC installed solely for that program. Once a day, or at the moment of a significant event, the data was transfered from both computers to a third PC where the processing took place. Due to it's continuous recording format, the SOUFRIERE program detected many small earthquakes that were not recorded by IASPEI. On September 1999, both systems were replaced by the ViSeis continuous recording program.

Seismic stations operated by the Puerto Rico Seismic Network in Puerto Rico and Virgin Islands

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