An Assessment of Seismic Body-wave Magnitudes Published by the Prototype International Data Centre

Abstract

A significant initiative in the reporting of global seismicity began in January 1995 with the publication of daily “Reviewed Event Bulletins” (REB's), a few days in arrears. This work was and still is done in the context of international efforts aimed at verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). When it was finalized in 1996 the CTBT specified that the seismic monitoring network of the International Monitoring System (IMS) would consist of 50 primary stations contributing data continuously to an International Data Centre (IDC) in Vienna, plus 120 auxiliary stations that record continuously but contribute data to IDC only on request (Richards, 2002). Until IDC began daily operations on 21 February 2000, the daily REB was published by the Prototype International Data Centre (PIDC) and a predecessor organization. We shall refer to all the REB's from 1 January 1995 to 20 February 2000 as having been published by PIDC. This paper focuses on the PIDC teleseismic body-wave magnitudes ( mb ). They are important as a modern effort to measure short-period magnitudes based on what is expected to become a fixed network of global stations, all operating in a standardized way. Although seismic magnitudes are intended to be a characteristic of the source, it is well known that in practice they are influenced by numerous additional factors such as the particular set of stations reporting individual magnitudes, the instrument responses, and the details of how each station magnitude is assigned. Global bulletins of seismicity, including mb values, have long been reported, months in arrears, by the Preliminary Determination of Epicenters (PDE) and Earthquake Data Report (EDR) of the U.S. Geological Survey's National Earthquake Information Center (USGS NEIC). They have also been reported, about two years in arrears, by the International Seismological Centre (ISC), based in England. To obtain its …