The International Seismological Centre (ISC) is a non-governmental, non-profit making organization charged with the final collection,analysis and publication of standard earthquake information from all over the world.
Earthquake effects have been noted and documented from the earliest times, but it is only since the development of earthquake detecting instruments within the last hundred years that a proper study of their occurrence has been possible. The need for international exchange of readings was soon recognized by Professor John Milne, whose work resulted in the International Seismological Summary being set up immediately after the First World War.
After Milne's death, the International Seismological Summary operated with funding principally from colleges of U.K. universities under the directorship of several professors of seismology at Oxford University, and Sir Harold Jeffreys (Cambridge).
The present International Seismological Centre was formed in Edinburgh in 1964, with Dr. P.L. Willmore as its first director, to continue the work of the International Seismological Summary (ISS), which was the first gathering of all observations of earthquakes world-wide.
In 1970, with the help of UNESCO and other international scientific bodies, the Centre was reconstituted as an international non-governmental body, funded by interested institutions from various countries. Initially there were supporting members from seven countries, now there are more than 50, and member institutions include national academies, government departments and universities. Each member contributing a minimum unit of subscription or more, appoints a representative to the Centre's Governing Council, which meets every two years to decide the Centre's policy and operational programme. Representatives from UNESCO and the International Association of Seismology and Physics of the Earth's Interior also attend these meetings. The Governing Council appoints the Director and a small Executive Committee to oversee the Centre's operations.
Most of the ISC budget is financed by Members' subscriptions but since 1978 a new category of Associate Membership has been available to organizations in the commercial sector, such as insurance offices, engineering enterprises and exploration companies, which have a professional need for the Centre's results, and wish to contribute to its continuing operations. Both members and associate members are afforded certain privileges.
In 1975, the Centre moved to Newbury in southern England to make use of better computing facilities there. The Centre subsequently acquired its own computer and in 1986 moved to its own building at Pipers Lane, Thatcham, near Newbury. The internal layout of the new premises was designed for the Centre and includes not only office space but provision for the storage of extensive stocks of ISS and ISC publications and a library of seismological bulletins, journals and books.
Since 1957 the manipulation of the large volume of data has been mainly carried out by computer. Up until then ISS locations were determined manually with the help of a large globe. The ISC now uses a network of workstations accessing a relational database of nearly 50 Gbytes of on-line data.
The analysis of the earthquake data is undertaken in monthly batches and begins after at least 18 months to allow the information used to be as complete as possible. Although much of the work would be impossible without the Centre's large suite of computer programs, the final editing of events large enough to be detected by several independently operated networks is always carried out by seismologists who scrutinize the output for unlikely events and chance misassociation of readings.
During analysis the computer program first groups origin estimates from different agencies and then associates the individual station readings with the most likely event. In a typical month more than 200,000 station readings are analysed leading to an average of 10,000 events per month being identified, of which some 4,000 require manual review. Misassociations and other discrepancies are rectified and the remaining unassociated readings are searched for new events and previously unreported earthquakes are added to the database. The total number of events listed each month is several times greater than those obtained by any other world-wide location service and results from ISC's goal to provide a fully comprehensive list.
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