The Nicaraguan Seismic Network registered in May, 1998, a number of 161 seismic events. The majority of them were located in the subduction zone off coast of the Pacific Ocean. An event with macroseismic intensity VI was felt on May 6 in the town of Masaya and surroundings, generated by a shallow earthquake (Mc=3.4) located at an epicentral distance of only 3 km to the city. It was followed by an aftershock swarm which lasted several days. Seismic events occurred in the volcanoes San Cristóbal, Telica, Cerro Negro, Momotombo and Apoyeque. The volcano‑seismic activity of San Cristóbal volcano remained low.
The Nicaraguan Seismic Network counts now with 20 telemetric seismic stations. Ten of them are located in volcano complexes. The data are digitally recorded and processed at Managua data center, which in turn has also a 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 unusual behavior of the seismic signal in the volcanoes would also be reported to enable preventive measures against the negative effects of dangerous phenomena 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, El Salvador, Honduras, Costa Rica, Panama. 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 the front page.