International Seismological Centre - Purpose

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 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 worldwide location service and results from ISC's goal to provide a fully comprehensive list.