The Impact of Digital Data on Seismic Bulletins
D Storchak and R J Willemann
Internationally funded to publish a definitive global seismicity bulletin, the ISC has avoided changes that might alter the fundamental content of the Bulletin. This conservative approach has been mandated by the need for hypocentres, magnitudes and other earthquake parameters that are as uniform as possible. It is now possible, however, to compute new locations and magnitudes for the ISC's entire Bulletin back to 1964 and to provide data more flexibly, for example giving users residuals with respect to their own choice of location or earth model. Thus, the ISC could now change models or procedures occasionally as required to best serve seismologists, and compute new parameters of past events according to the updated practices. But seismologists are changing their practices to take better advantage of broadband digital data in studying earthquake physics, earth structure, explosion monitoring, seismic hazards and seismotectonics. To serve all these needs, even more fundamental changes in the Bulletin may be required. Within the next few years, the ISC plans to begin experimental measurement and publication of waveform measurements and earthquake parameters that are not now routinely catalogued. Possible measurements include automated later phase picks, surface wave dispersion, and spectral measurements. Possible earthquake paramters include source time function parameters, waveform-based depths, and relative locations from waveform-based relative arrival times. We welcome input from the community on the parameters and algorithms that are most likely to prove useful and reliable.