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| Titel |
The contribution of NDC bulletins to quality assessments of the REB - a case study for Romania |
| VerfasserIn |
F. Kebede, K. Koch |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250026538
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| Zusammenfassung |
| To make available a high quality product to state signatories, continuous quality assessments
are carried out at the International Data Centre (IDC) of the Provisional Technical Secretariat
(PTS) for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). One of the
means of assessing the Reviewed Event Bulletin (REB) quality is to compare the bulletin
with independently compiled bulletins. In particular, bulletins contributed by National Data
Centres (NDCs) are of special interest because it can be expected that an NDC locates events
in and near its national borders with great accuracy and that the resulting seismic bulletin is
complete to lower magnitudes than the IDC’s REB. Hence, the purpose of a bulletin
comparison study of the REB with any NDC bulletin is (1) to evaluate the accuracy of IDC
locations; (2) to assess if the IDC has missed events of considerable size; and (3) to
investigate if all data from relevant IMS stations were adequately used in the IDC
automatic processing and interactive analysis of the events in the corresponding
region.
For this study the seismological bulletin of the Romanian NDC (ROM_NDC) for the
years 2007 and 2008 has been used, this bulletin being made available to the IDC since the
System-Wide Performance Test. The bulletin contains 393 (262 in 2007 and 131 in 2008)
events. All events were located within or very close to the Romanian borders based on data
from Romanian national network stations, with a maximum magnitude of MD = 5.6.
On the other hand the IDC REB contains a total of 31 (9 in 2007 and 22 in 2008)
events in the study period and region under consideration (43oN to 49oN; 19oE to
31.5oE).
From the comparison a total of 25 IDC events were found that match to corresponding
ROM_NDC events. The location difference for these matched events is less than 0.3o, except
for one outlier with 0.95o difference related to depth inconsistency. About 32% of the
matched events do not have intersecting error ellipses, 56% have partially intersecting error
ellipse areas, and for a minor part of the matched events (12%) the ROM_NDC error
ellipse area is within the IDC error ellipse area. Considering the magnitude estimates
for matched events, it is found that IDC mb magnitudes are, on average, about
one magnitude unit lower than ROM_NDC duration magnitudes. The maximum
magnitude for unmatched ROM_NDC events is MD=4.6. Investigation of these
events showed that events with MD > = 4.0 could be saved as REB events, hence the
detection level for REB events in and near Romania could be as low as mb=3.0. |
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