IDA Update

Holly Given, Project IDA, University of California, San Diego

Happy Anniversary! 1995 marks 20 years of Project IDA, the first globally deployed, digitally recorded network to expand significantly the bandwidth of seismology by making fundamental new observations of the Earth's free oscillations. Also, on August 6 of this year, our friend Dr. Cecil H. Green celebrated his 95th birthday. Along with their numerous other gifts to academic geophysics, Cecil and his late wife Ida Green were early patrons of the IDA Network. The first IDA grant from NSF to principal investigators Freeman Gilbert and Jonathan Berger was backed by a pledge from the Greens to buy instruments and the first IDA station began operating near Canberra, Australia (CAN) in January 1975, quickly followed by stations NNA and PFO. The continued support of the Greens helped the IDA Network to reach a steady-state configuration of about 20 stations by 1983. This "original configuration" IDA Network using modified feedback gravimeters was a unique facility for many kinds of seismological studies.

By the mid-1980's, broadband seismographic systems that could accurately record ground motions from a few milliHertz to a few Hertz were a reality. The vision of a broadband network with 100 stations or more uniformly covering the globe required a coordinated effort by the university community, and led to the formation of the IRIS Consortium in 1985. Project IDA, again with help from Cecil and Ida Green, committed to upgrade and expand the IDA Network as an integral part of the IRIS program. The first of the new generation of broadband IRIS/IDA stations were PFO and ESK installed in 1986.

Today, Project IDA operates 27 stations of the Global Seismographic Network, including six new locations since the last IDA Update in the Fall 1994 IRIS Newsletter; three of these are on islands in the Southern hemisphere, and three are on continents in the Northern hemisphere. Stations ASCN and SHEL are located on Ascension Island and the Island of Saint Helena, respectively. Both small islands are territories of the United Kingdom in the southern Atlantic Ocean. Both use Teledyne Brown KS54000 borehole seismometers as the basic broadband sensors and Streckeisen STS-2s as short-period sensors; SHEL is the first IRIS station to deploy the STS-2 in a shallow (6 meter) borehole using a "cradle" designed at IGPP that allows remote leveling. Saint Helena, where Napoleon I died in exile in 1821, is in some ways the most remote IRIS/IDA station. There is no airport, and a mail/passenger ship calls once per month. ASCN and SHEL are accessible in near-real time and participate in the IRIS SPYDER system. ASCN began operation on October 1, 1994, and SHEL on June 19, 1995.

Station MSEY is located on the island of Mahe, Republic of the Seychelles, in the Indian Ocean. It began operation on May 15, 1995 with a KS54000 borehole seismometer and a Guralp Systems CMG-3T in a shallow (6 meter) borehole as the short-period sensor. MSEY is the first IRIS/IDA station to co-locate continuously recorded, geodetic quality GPS data in collaboration with the GPS Networks and Operations group at Jet Propulsion Laboratory. The seismometer borehole casing itself, cemented to granitic rock to 100 meters depth, forms the fiducial benchmark for the GPS receiver. An antenna mount designed by JPL engineers can be removed and accurately re-installed if work is required in the borehole. MSEY is accessible in near-real time.

Picture: GPS antenna mount and benchmark coupled to the seismometer casing wellhead at MSEY (Mahe Island, Seychelles; photo by Garth Franklin, JPL).

Station JTS, near the small town of Las Juntas de Abangares ("Juntas") in northwest Costa Rica, began operation on April 23, 1995. It is a joint station with Costa Rica's national network operated by the Volcanological and Seismological Observatory of Costa Rica (OVSICORI) under the direction of Dr. Federico Guendel. JTS is located on former mining property; the current owner, who is also the station operator, relocated from Switzerland some years ago to explore for gold. For a sensor environment, we enlarged an old dynamite storage tunnel and built a pier about 13 meters back into the hillside for the STS-1, STS-2, and FBA-23 sensors, adding doors to provide some isolation from the outside. A dedicated phone line was installed from JTS to OVSICORI, which is on the Internet. Costa Rica has officially submitted JTS for use in the "GSETT-3" experiment on global seismic data exchange currently being carried out by the United Nations Conference on Disarmament.

Station NIL in Nilore, northern Pakistan, is in collaboration with the Pakistan Institute of Nuclear Science and Technology (PINSTECH), which had previously operated a station at this location with a Teledyne Geotech KS36000 borehole sensor. NIL began operation as an IRIS GSN station December 18, 1994 using the KS54000 borehole sensor with an STS-2 and FBA-23 deployed on a pier in a nearby building. NIL became accessible in real time in October.

KURK in Kurchatov, Kazakhstan, is located on the grounds of the former Soviet underground nuclear test site near Semipalitinsk and is operated by the National Nuclear Center of Kazakhstan. The sensors (STS-1's, STS-2, and FBA-23) are in an instrument room in a 25-meter deep vault complex. KURK began operation March 26, 1995. KURK is not yet accessible in real time. More on the configuration of IRIS (GSN) stations operated by Project IDA can be obtained by accessing our home page (select "map of IDA stations" and then click on the station's symbol).

On July 21, 1995, RPN (Easter Island, south Pacific Ocean) became the sixth IRIS/IDA station that is an Internet node with full-period connectivity, thanks to a cooperative agreement with NASA and the University of Chile. These stations provide routine and continuous real-time telemetry of broad band (BH*) and very long period (VH*) data.

Site preparation has been nearly completed at CMLA (Cha de Macela, Sao Miguel Island, Azores) and EFI (Mt. Kent, East Falkland Islands) and are the next installations planned. Site reconnaissance trips were recently carried out in Uganda, and the Cocos (Keeling) Islands in the Indian Ocean. We are happy to announce the addition to our staff of development engineer Arthur Endress. Art is familiar to many in geophysics from his long career in the instrument group at Teledyne Geotech; recently he has worked as a field engineer for Schlumberger International. Field technician Phil Porter also has joined Project IDA after acquiring years of valuable experience with the Kyrgyzstan Network (KNET) group at IGPP.

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