Summary report of the workshop on the U.S. use of surface waves for monitoring the CTBT Page: 4 of 16
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Surface waves are well suited to be the first topic for such a small CTBT workshop
for three reasons.
1) It became apparent at the Orlando meeting that several research groups in academia,
industry, the National Laboratories, and AFTAC are working on related research problems
in utilizing surface waves in monitoring the CTBT. Although this work is being
performed at different scales (regional, continental and global) and in several different (but
overlapping) geophysical areas, there is considerable common ground for comparison,
peer-review, and, ultimately, consensus on how surface wave measurements are carried
out and used for CTBT purposes. To facilitate this, the two Thursday morning sessions
were devoted to revealing the results of a series of tests in which the participants engaged
prior to the meeting. Participants were asked to supply group velocity measurements for
10 specified event-station pairs as well as a 20 s Rayleigh wave group velocity map in the
region from 10 N to 50 N and 25 E to 100 E. The purpose was to understand the causes
of differences revealed by the comparisons, and to provide a common basis for discussion.
2) It is clear that these disparate research efforts and results need to be integrated with the
goal of optimizing the U.S. CTBT monitoring capability. The first Thursday afternoon
session was devoted to hearing from the major customers and funders of this research,
AFTAC (hosts the NDC), DOE (developing the Knowledge Base), and NTPO/DSWA
(funding/managing PRDA contractors).
3) Finally, surface waves have a long-standing role in seismological aspects of treaty
monitoring. They play a major role in earthquake-explosion discrimination, via the use of
the surface-wave body-wave magnitude ratio (Ms:mb). They have an even longer standing
role in providing information about velocity structures in the crust and upper mantle that
may be used to improve U.S. capability to locate and characterize seismic events. The
remaining sessions in the workshop were designed to address some of these issues.
IL. Summary of Workshop
The consensus of the participants was that workshop was successful in that it took
a positive first step toward achieving its major goals. As discussed later in this report, the
fulfillment of the goals of the workshop will require continued cooperative research, data
exchange and follow-up meetings in the future.
The first Thursday morning session focused on a comparison of group velocity
measurements for a test set of data (see Fig. 1) obtained by different groups. The
participating groups were from the University of Colorado (CU, Levshin, Ritzwoller), Los
Alamos National Lab (LANL, Jones, Patton), Lawrence Livermore National Lab and
associates (LLNL, Walter, Rodgers, Hazler and McNamara), Maxwell (Stevens), and
Saint Louis University (SLU, Ammon, Herrmann). The test data set displayed three
unanticipated timing errors. Two were in the range from 40 to 50 seconds, which were
large enough to induce error but not necessarily be obvious if only the surface waves were
examined. Another timing error appeared in a SEED volume received from the
Incorporated Research Institutions for Seismology (IRIS) Data Management Center
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Ritzwoller, M. & Walter, W. R. Summary report of the workshop on the U.S. use of surface waves for monitoring the CTBT, report, September 1, 1998; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc673296/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.