During 13 to 29 August 1997 the Geophysical Institute of the Escuela Politecnica Nacional (IG-EPN) in Quito, Ecuador, and the Charles Darwin Foundation installed the first seismographic network ever to be established in the Galápagos Islands, site of the well-documented Gal pagos mantle plume with its active volcanism. The network consists of three telemetered seismic stations located at Pta. Espinosa on the NE end of Fernandina Island (Station FERN; 0°16.0'S, 91°26.7'W, elev. 3 m), on the NE corner of Sierra Negra caldera (Volc n Chico) on Isabela Island (Station VCHI; 0°47.5'S, 91°04.0'W, elev. 1,490 m), and at Bartolome Island, at the E end of Santiago Island (station BART; 0°16.9'S, 90°33.1'W, elev. 100 m). The IRIS project is scheduled to install a wide-band station on Santa Cruz Island in the coming weeks. Once the IRIS device is operative, these four permanent stations will effectively constitute an array in the form of a parallelogram that will cover the western center of the archipelago.

The importance of the new network lies in its ability to monitor the active volcanoes of Fernandina, Volcán Chico, and Sullivan Bay, as well as more distant volcanic centers. In addition the new network will detect tectonic activity generated in this mantle-plume setting or associated with the NNW-SSE and ENE-WSW structural lineaments that apparently control the distribution of volcanoes and that were first recognized by Charles Darwin. The data will also provide better hypocenter locations for seismic events related to subduction of the Nazca and Cocos plates along the South American and Central American coasts.

The instrumentation includes vertical 1-Hz seismometers (Mark Products L-4C) set in massive lavas whose responses have attenuations of 12 to 18 dB. State-of-the-art electronics and radio telemetry as well as solar panels complete the systems. The seismic signals are continuously telemetered to the Charles Darwin Scientific Station located at Academy Bay on Santa Cruz Island. Data acquisition is carried out with the IASPEI software and the events sent via email to IG-EPN for processing.

After only a few days of operation, several low-magnitude A-type earthquakes were detected and tentatively located in the southern part of Isabela Island near Volcán Chico. Several medium-size events, well-located on the South American continent by regional and international seismographic networks, were recorded by the new Gal pagos net. Once the IRIS station is functioning, better identification of locations will be possible. It is hoped that in the future, if funding becomes available, two or three more seismic stations will be installed on other active volcanoes.

This project received financial aid and help from the USAID Mission in Quito, the Charles Darwin Foundation, the Escuela Politecnica Nacional, the Galápagos National Park Service, the Ecuadorian Air Force, the Civil Aviation Authority, Banco del Pacifico, the Ecuadorian Institute Electrification, TAME, ORSTOM, and the Charles Darwin Scientific Station.

Geological Summary. Special announcements or information of general interest not linked to any specific volcano.

Information Contacts: Minard L. Hall, Escuela Politecnica Nacional, Casilla 2759, Quito, Ecuador.