Data Collection at the International Seismological Centre
R J Willemann and D A Storchak (2001)
Seismological Research Letters, 72, 440-453.
The International Seismological Centre (ISC) prepares a global seismicity catalog that is intended to represent a comprehensive summary of hypocenters and phase readings for all sufficiently large earthquakes. There is no firm definition of "sufficiently large" and in practice the completeness threshold varies from place to place [Willemann, 1999]. But the original intention was to relieve seismologists of the need to gather readings from multiple sources and re-compute locations as part of individual research projects. At a minimum, therefore, the ISC aims to include all earthquakes in its Bulletin that might be recorded by more than one independently operated network. Thus, the mission of the ISC has grown as data collection becomes more comprehensive.
The completeness of the ISC Bulletin, in terms of both earthquakes and phase readings, is essential to its utility for research. Completeness is facilitated by the ISC's status as a non-governmental, non-profit organization in working relations with UNESCO and by waiting nearly two years for final analyses of regional and national bulletins from around the world. As a result, the ISC Bulletin includes more than twice as many earthquakes annually as any other global seismicity catalog, and for most earthquakes more phase readings. The cumulative Bulletin database thus is the preferred resource for a variety of global and broad regional studies in seismology ranging from seismicity [e.g., Engdahl et al., 1998] to tomography [e.g., Bijwaard et al., 1998; Hilst et al., 1997].
The enormous task of producing a comprehensive global bulletin is accomplished by building on, rather duplicating, the analysis that is carried out at individual stations and networks. The sources from which data analyses are collected and the means by which they are integrated into a processing system limit the completeness and accuracy of the ISC Bulletin. Our purpose in this paper is to explain the system in order to help seismologists understand these limitations and avoid misinterpretions.
Complete paper in PDF format (Copyright 2001 by the Seismological Society of America. Made available by permission)