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| Titel |
The unique contribution of the IDC Reviewed Event Bulletin to global seismicity catalogues |
| VerfasserIn |
Karl Koch, Fekadu Kebede |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042136
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| Zusammenfassung |
| For monitoring the Comprehensive Nuclear-Test-Ban Treaty (CTBT) the International
Monitoring System (IMS) network is currently being established that will eventually consists
of 241 seismic, hydroacoustic and infrasound stations. The final result of processing and
analysis of seismological and other waveform technology data from these stations is the
Reviewed Event Bulletin (REB), which has been issued by the International Data Center
(IDC) under provisional operation since February 2000 on a daily basis, except for a total of
28 days. The nearly 300,000 events produced since then correspond to more than 25,000
events per year. As an accompanying effort to the bulletin production at the IDC, quality
assurance work has been carried out for the REB for the years from 2000 to 2008 through
comparisons to similar bulletins of global seismicity, issued by the ISC and the National
Earthquake Information Center (NEIC) of the United States Geological Survey.
The comparisons with the NEIC bulletin concentrate on a timely identification of
larger events that were either missed during interactive analysis at the IDC or which
have been significantly mislocated. For the scope of this study the comparisons
with the ISC bulletin are the focus, as this bulletin provides the most complete
reference to global seismicity, even though it becomes available only after about two
years of event occurrence. In our quality assessments we aimed at evaluating the
consistency of event locations for common events, i.e. found in both the REB and the ISC
bulletin having been relocated by ISC; the degree and the geospatial location of
the events only produced in the REB and verified not being bogus, and those ISC
relocated events not contained in the REB and which were missed during IDC
analysis.
Even though the seismic component of the IMS network with its maximum 170
seismometer stations is a sparse teleseismic network, locations differences of less than 1Ë
(0.5Ë ) are observed, on average, for about 94% (85%) of the common events, as obtained
from the ISC bulletin comparisons for the years 2000 to 2006. On the other hand, only
0.25% of such events were located more than 5Ë apart by the IDC and the ISC.
The number of events of significant magnitude missed by the IDC is small and
related predominantly to lack of sufficient number of observed arrivals to define an
event.
The unique contribution of the REB to global seismicity catalogues is expressed by the
significant number of REB events that are solely reported in the ISC bulletin. Over the most
recent years 2004-2006 the REB and ISC bulletin include about 20,000 common events
which were reprocessed by the ISC. This compares to a steadily rising number of solely
contributed REB events from more than 5,000 events in 2004 to nearly 7,500 events in 2006,
i.e. a quarter to a third events more. These unique IDC events are mainly in remote and
oceanic areas. A more important aspect, however, is the number of unique IDC events at
depth. Below a depth of about 300 km there are nearly any ISC events not detected by the
IMS network, while the number of events at larger depths and only detected by
the IMS is significant. As conclusion it is found that the IDC REB is a valuable
source for studies of deep seismicity occurring within the global subduction zones. |
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