Existing Infrastructure for International Exchange of Seismic Data Raymond J. Willemann GEM Technology, Washington, D.C. IASPEI:Includes commissions for discussion and to establish standards ISC:Collects, merges,and re-distributes seismic bulletin data FDSN:Helps broadband seismic networks to co-ordinate their activities

The International Association of Seismology and the Physics of the Earth’s Interior (IASPEI) is one of 7 associations that comprise the International Union for Geodesy and Geophysics. IASPEI Objectives The primary objectives of IASPEI fall into three categories: Promotion of the scientific study of problems related to earthquakes and other seismic sources, the propagation of seismic waves, and the Earth's internal structure, properties, and processes. Initiation and coordination of the conduct of research and of scientific exchanges and discussions that are dependent on cooperation among a number of countries. Facilitation of research and education in basic and applied seismology, especially in countries that are in the process of working towards full scientific development.

At IASPEI’s 32 nd General Assembly in Sapporo, Japan during 2003, the association adopted this resolution: IASPEI Resolution RECOGNIZING the need to accurately locate earthquakes and determine earthquake size, and compile complete earthquake bulletins, URGES all operators of seismic stations and networks to deposit unique station codes with the international registry maintained by the International Seismological Centre and by the World Data Centre for Seismology, Denver, and to freely share the coordinates of all seismic stations, URGES all operators of seismic stations and networks to keep accurate record of instrument response and performance.

Why It Is Useful To Have Data from More Stations Seismology is advancing beyond computing “formal” estimates of uncertainty that are based on questionable statistical assumptions. To estimate “absolute” location uncertainty, seismologists must calibrate new techniques using very accurate locations. Many seismologists accept a location computed by a local network as absolutely accurate within 5 kilometers only if it is computed from arrival times at stations At least one of which is within 30 km of the earthquake At least ten of which are within 250 km of the earthquake With a very good distribution around the earthquake Local networks may be re-configured frequently to meet new needs, so using their data depends on detailed knowledge of the network. Thus, seismologists recognize that there may be advantages from arranging some exchanges of local network data individually.

How Much Data Should be Exchanged Internationally Regional networks cover a broader area but with somewhat more sparsely distributed stations. Regional networks usually have a more standardized configuration, so data from them can be used with greater confidence by more seismologists. Many seismologists accept a location computed by a regional network as absolutely accurate within 20 kilometers if it is computed from arrival times at seismic stations that are all within 1000 km of the earthquake have very good distribution around the earthquake To achieve a very good distribution around an earthquake often requires at least ten seismic stations. Because China is so large, several hundred stations are needed to achieve a good distribution of regional stations around all of the earthquakes in China.

Role of the ISC The International Seismological Centre (ISC) has facilitated international exchange of seismic bulletin data since ISC collects and merges seismic bulletin data from more than 100 seismic networks, and provides the resulting combined bulletin without charge to seismologists all over the world. est.

Stations Reporting to the ISC Blue triangles show station locations. Green, yellow and red shading shows least distance to stations with good distribution around an earthquake.

The China Earthquake Administration (CEA) sends a monthly bulletin to the ISC. But it is based on only 24 stations in China. ISC is funded by contributions from more than 50 seismological organizations, including the CEA.

Measures of absolute location accuracy are much worse for earthquakes in China than in most other countries that monitor earthquakes well.

FDSN The FDSN is a “mutual help” organization, within which network operators share ideas, software, and a data archive. The FDSN provides a forum for: developing common minimum standards in seismographs (e.g. bandwidth) and recording characteristics (e.g. resolution and dynamic range); developing standards for quality control and procedures for archiving and exchange of data among component networks; coordinating the siting of additional stations in locations that will provide optimum global coverage.

Summary Knowledge of earthquake hazard can advance as a result of unrestricted sharing of seismic data, including seismic station information, bulletins, and waveforms. The International Association for Seismology and the Physics of the Earth’s Interior (IASPEI) urges all seismic networks to share information about all seismic stations. Seismologists would recognize unrestricted distribution of a CEA seismic bulletin based on several hundred stations in China as an important and significant improvement in data exchange. The International Seismological Centre (ISC) provides a reliable and very efficient mechanism for internationally exchanging seismic bulletin data. The Federation of Digital Seismograph Networks (FDSN) can provide assistance in sharing data from many more stations, including multiple networks within any country.