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Determination of the Seismic Moment Tensor Using Surface Waves Recorded by the IMS Network
COMPREHENSIVE NUCLEAR TEST BAN TREATY ORGANIZATION VIENNA (AUSTRIA) PREPARATORY COMMISSION
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The Provisional Technical Secretariat PTS of the Comprehensive Nuclear-Test-Ban Treaty Organization CTBTO has been ramping-up the installation of the International Monitoring System IMS consisting of a network of seismic, hydroacoustic, infrasound, and radionuclide stations, since its inception in March 1997. Data from this network are automatically processed at the International Data Centre IDC to produce, within a few hours, a series of automatic bulletins called the Standard Event Lists SEL1, SEL2, SEL3. After analyst review and correction as necessary the Reviewed Event Bulletin REB is produced. Additional information about characterization of an event as an earthquake or otherwise is also available in the Standard Event Bulletin SEB shortly after production of the REB. The Comprehensive Nuclear-Test-Ban Treaty CTBT states that the IDC will apply standard event screening criteria to each event formed. The objective of this process is to filter out events that are considered to be consistent with natural or non-nuclear man-made phenomena, leaving a reduced set of events that may require further examination. In Annex 2 of the Protocol to the Treaty, the focal mechanism is listed as possible event screening parameters. In order to provide a focal mechanism and increase the number of elements potentially useful as screening attributes, we have in the last two years implemented two methods for moment tensor MT inversion. One method is based on the P body waves and the other on surface waves. Implementation of these sophisticated inversion methods has led to improvements in the calibration of the broad-band seismic network, notably quality control of the instrument responses. We report here on the results obtained from the implementation of the surface-wave MT inversion, which uses both Rayleigh waves and Love waves.
APPROVED FOR PUBLIC RELEASE