The Nicaraguan Seismic Network located in January, 1998, a relatively low number of 99 seismic events. The mayority of them were located in the subduction zone off coast of the Pacific Ocean. Seismic events occurred also in the volcanoes San Cristóbal, Telica, Cerro Negro, Momotombo. There were felt several seismic events in the Cofradía seismic zone, near Managua, but only two of them was recorded by the seismic net.
The activity of San Cristóbal volcano calmed down, the seismic tremor was much lower than in the previous months and there was little visible volcanic activity in the crater. The seismic station at Telica volcano did not work well in the beginning of January. In the second half of the month it was observed that the relativly stable seismic activity which prevailed in the prevous months (about 150 events per day) changed into another mor unstable state. The number of events differs strongly from day to day and periods of tremor occur.
With the help of two specialists of the US Geological Survey the data processing equipment for the volcano monitoring in Nicaragua was improved in the Seismic Data Center of INETER. The center can now not only detect and register seismic events in the volcanoes but performs a continous recording of the seismic amplitude (RSAM) and the spectral parameters of stronger signals (SSAM).
The Nicaraguan Seismic Network counts with 19 telemetric seismic stations, 9 of them located in volcano complexes. The data are digitally recorded and processed at Managua data center, which in turn has also set of seismometers . Any seismic event detected by the data acquisition routine is processed regularly within a short time by the seismologist on duty. In case of a strong event the system emits an acoustic signal and the seismologist determines immediately the parameters of the event and sends within minutes a report to the Nicaraguan authorities and the mass media. Any inusual behaviour of the seismic signal in the volcanoes would also be reported to enable preventive measures against the negative effects of dangerous fenomena in the volcanoes (beginning eruption, land slides, strong degassing).
The Monthly Bulletin is published in the first days of the following month, after having revised the preliminary data. It is distributed in Nicaragua to governmental organizations and mass media, in Central America to cooperating institutions in Guatemala, Honduras, Costa Rica, Panamá. Furthermore it is sent to several cooperating institutions in South America, North America and Europe. Phase data and waveforms can be obtained writing to the address on first page.