The International Seismological Centre is a non-governmental, nonprofit organisation charged with the final collection, definitive analysis and publication of global seismicity. The ISC was formed in 1964 as an international organisation independent of national governments that would carry on the work of the International Seismological Summary in collecting and analyzing seismic data from around the world, and particularly to handle increased flow of data from the World-Wide Standard Seismograph Network, also established that year. The ISC considers its prime task to be the collection and re-analysis of all available earthquake seismic date in order to produce definitive data on earthquakes. The ISC's catalog is considered "the most complete and authoritative final depositary of global earthquake parameter data."
Purpose
The main scientific goal of the Centre is the definitive compilation of earthquake information and the readings on which they are based. Collection of reports of earthquake effects is also an important part of its operation and the Centre recomputes the location and occurrence time of earthquakes worldwide, making use of all available information. 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 online 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 scrutinise 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 worldwide location service and results from ISC's goal to provide a fully comprehensive list.
Data products
The data the ISC collects and processes forms the basis of several data products.
ISC Bulletin
The is the main collection of ISC data, organised by events. After approximately two years all of the data collected for an event is reviewed and the hypocenters and magnitudes recalculated; the Reviewed Bulletin is "regarded as the definitive record of the Earth's seismicity." Most of the other data products are subsets of the Bulletin.
ISC-EHB Bulletin
The original contains events from 1960 to 2008 whose hypocentres were recalculated by the algorithm of. This has been replaced by the , which extends the catalog to 2013.
ISC-GEM Catalogue
The catalogs magnitude 5.5 or greater earthquakes suitable for modeling and assessing seismic hazard and risk. Epicentral locations and hypocentral depths were recalculated from original travel time data using a consistent velocity model. Magnitudes are expressed as moment magnitude scale, taken either from reliable published values of seismic moment or from recalculated values of surface wave or body wave magnitude, converted to Mw using empirical relationships.
The database contains 9280 earthquakes and explosions whose hypocenters have been located within 10 km or less, often in conjunction with on-site studies. These events have seen selected to better "see" the Earth's structure, and to provide references to which seismic networks can be more accurately calibrated.
