HA3, Juan Fernandez Islands, Chile

The Juan Fernández Islands — of which Robinson Crusoe Island is the largest — is a sparsely inhabited island group situated in the Southern Pacific Ocean about 670 km west of the Chilean mainland. Volcanic in origin, the islands have a total area of 181 km² and a population of about 630, virtually all of whom reside in the capital, San Juan Bautista, on the north coast.  Administratively, the archipelago belongs to Chile's Region of Valparaíso, which also includes Easter Island.
The archipelago was originally discovered by chance on 22 November 1574 by the Spanish sailor Juan Fernández, who was sailing between Peru and Valparaíso and deviated from his planned course. He named the islands Más Afuera, Más a Tierra, and Islote de Santa Clara. In the 17th and 18th century it was used as a hideout for pirates and as a penal colony.

These isolated islands were home to the sailor Alexander Selkirk for four years and inspired Daniel Defoe’s famous adventure novel, Robinson Crusoe, published in 1719.  This fictional autobiography was most likely influenced by the real-life events of Selkirk, a Scottish castaway who lived on the Pacific island of Más a Tierra whose name was changed to Robinson Crusoe Island in 1966, which today hosts the International Monitoring System's (IMS) infrasound station IS14.

The volcanic origin is more than obvious in some parts of the island. Like Easter Island, the Juan Fernández Archipelago is up to four million years old. Its three islands, Robinson Crusoe, Alexander Selkirk and Santa Clara, are the only elevations of an extensive submarine ridge that is approximately 400 km long and 50 km wide.

The three islands of the archipelago rise steeply out of the Pacific, with few beaches and a limited number of protected bays, possibly formed by ancient volcanic craters.

HA3 covers large areas of the Southern Pacific Ocean and the Southern Ocean. Essentially identical in design to the hydroacoustic station in Cape Leeuwin, Australia, this is one of six IMS hydrophone stations, which utilizes an underwater microphone (hydrophone) to detect signals originating from underwater explosions.

The isolated location far from major human settlements or traffic make the Juan Fernández Islands an ideal site for both IMS stations which are located there, HA3 and infrasound station IS14. The Central Processing Facility (CPF) of the both IMS stations is housed in the capital town of San Juan Bautista. From here the data are transmitted in near real time to the International Data Centre halfway around the world in Vienna, Austria.

All four CTBT verification technologies are represented in Chile: Apart from HA3 and IS14, Chile hosts two auxiliary seismic stations, one other infrasound station and two radionuclide stations. 

Testing and Certification

The Factory Acceptance Test and Integration Testing for HA3 were completed in 2002, as was the installation of shore processing equipment in the shore facility. The link to the Global Communication Infrastructure (GCI) was approved in early 2003, after which the underwater segment was installed and data flow to Vienna was established. After a 2003 operations training and station visit, HA03 was transferred to IDC operations.

Two underwater cables, 41 km and 28 km long respectively, connect the electronics bottles to the shore facility and are stabilized in shallow water to reduce wave-induced water motion. The station’s primary power source is provided by the town of San Juan Bautista but there is also a back-up generator provided at the station itself. The two triplets of hydrophones were tested through analyses of over 30 events, such as a major 5.9 magnitude earthquake that occurred in Mexico, 6,375 km from the station, but was picked up clearly by one of the hydrophones. The data availability was tested between March and July 2003 and was found to function at 99.9%, exceeding the 97% requirement. HA03 was therefore certified on 14 November as the fourth of a total of 11 hydroacoustic stations. Learn more about how the hydroacoustic technology works.