Modernizing the ISC location procedures: model evaluation (2007)

2nd Workshop
SW004, IUGG General Assembly, Perugia, Italy, 2007

The first workshop on modernizing ISC location procedures was held during the 2005 Santiago IASPEI General Assembly. Using a list of 156 well-located test events (GT0/GT5) selected from the IASPEI collection of Ground-Truth events, a number of prominent seismologists studied the effects of different location algorithms on location accuracies. The first workshop participants recommended that the ISC considers changing from the Jeffreys-Bullen (JB) velocity model, currently used in operations to locate seismic events, to a modern spherical Earth model with consistent travel-time tables for all major seismic phases. In particular the AK135 velocity model was recommended as the best candidate for this purpose.

To ensure that introducing new travel times into the ISC operation does not cause unwanted or unforeseen biases, the ISC was asked to produce its Bulletin for several data months using the AK135 model as well as JB. The version of the ISC Bulletin with JB and AK135 solutions, covering the period of Jan-Oct 2004, is now available to the seismological community. We encourage seismologists to use their local knowledge of different geographic and tectonic regions to conduct critical comparisons of the ISC JB and the experimental ISC AK135 locations.

The workshop in Perugia is planned as a combination of a poster and oral sessions. On day one the details of comparisons are to be presented during the poster session. On day two we plan a sequence of short 3-5 minute presentations from all poster authors, briefly informing the audience on the geographical area of interest, methods/additional data used as well as the main results of analysis. These short presentations are to be followed by discussion, which should result in a specific recommendation to the ISC Governing Council.

Approximately 15'000 events in Jan-Oct 2004 were located by the ISC using both JB and AK135 models

Those wishing to participate should submit abstracts to IUGG General Assembly: SW004 and contact the conveners so that the workshop could be planned in advance.


Johannes Schweitzer, NORSAR, P.O. Box 53, N-2027 Kjeller, Norway. Phone: +47-63805940, e-mail:

Dmitry Storchak, ISC, Pipers Lane, Thatcham, Berkshire, United Kingdom, RG19 4NS. Phone: +44-1635-861022, e-mail: