SEISMIC NOTES
INFORMATIVE BULLETIN OF THE PUERTO RICO SEISMIC NETWORK

No. 1 - 1998

INSTRUMENTATION AND ANALYSIS OF SEISMIC DATA IN PUERTO RICO

The seismometers with their respective seismographs and seismograms, are the instruments that serve as a starting point to be able to locate an earthquake, to calculate their magnitude and rupture mechanism of the Earth. The first seismic stations settled in Japan in 1880, later in Italy, and on 1887 in Berkeley, which is the oldest seismic station in continuous operation in the Western Hemishpere.

The first seismic station in Puerto Rico was installed in 1903 in the Fort of Count de Mirasol in Vieques.

Sismographic registry of one of the strongest reports (October 25) of the earthquake of October 11 of 1918 according to what was registered by the Vieques station.

The station was changed in 1926 to Guaynabo and in 1965 to Cayey, to the facilities of the Geophysical Observatory of San Juan which belongs to the United States Geologic Service (USGS). The data collected by this station
was merged with the seismic information data base of the USGS and for the region of Puerto Rico only events with greater magnitudes of 4-4.5 were reported.

In 1974 began the installation in Puerto Rico of a short period seismic network. This network, the Puerto Rico Seismic Network (PRSN), was installed by the USGS for the Electric Energy Authority (AEE) that was interested in studying the microseismicity of Puerto Rico to be able to evaluate the seismic vulnerability of the island for the construction of nuclear plants in Guayama and the North Coast. In 1982 the AEE passed the responsibility of the PRSN to the Center for Power and Environmental Studies of the UPR in Mayaguez and in 1987 to the University of Puerto Rico at Mayaguez. Since that year, the PRSN operates as a dependency of the Department of Geology of the Faculty of Arts & Sciences of the University of Puerto Rico at Mayaguez. At the present time, it is responsible by the maintenance, operation of the seismic instrumentation, processing, and the analysis and distribution of information of the seismic events of the region of Puerto Rico.

At the present time the PRSN operates fourteen short period stations, two of which are for the Army Corps of the United States to detect any change of seismic activity in the areas of the Cerrillos dams and Portugués at Ponce, and a three components broadband station in Maricao. The signals of the short period stations are sent directly or through repeaters to the data acquisition center in the facilities of the PRSN at the University of Puerto Rico at Mayaguez. Since 1991, there are computers that gather and make preliminary analysis of the signals and record registries of earthquakes. The data of eight of the stations are also registered in paper in the traditional drums.