Enhancing the Contribution of the T-Stations of the IMS Hydroacoustic Network to IDC Processing and Tsunami Warning.

摘要

The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is exploring methods to enhance the operational hydroacoustic processing system for its International Monitoring System (IMS). The hydroacoustic IMS network includes two types of stations, the in-water hydroacoustic stations, consisting of multiple sets of hydrophone triplets, and the land-based T-stations, consisting of multiple seismometers. Hydrophone triplets record signals that efficiently propagate in the SOFAR channel over large distances. Processing at the International Data Centre (IDC) classifies these signals into three types (T for underground-generated, H for in-water generated, and N for noise) and determines a direction of propagation, exploiting the multiplicity of sensors. Current efforts are underway to enhance the accuracy of the classification methods. However, the processing in place at the IDC is already quite mature for hydrophone stations. T-stations, on the other hand, present the double disadvantages of a lower detection threshold for in-water propagated hydroacoustic signals and high sensitivity to the geometry and geology of the seismometer emplacements, as opposed to hydrophone triplets located in the much more homogeneous water medium. In spite of these handicaps, the T-stations do already contribute to the IDC bulletins, mostly by detecting T-phases from events at a higher threshold than hydrophone stations. It would be desirable however to augment the quantity and quality of their contribution to the IDC bulletins. We are presenting the results of attempts at using the multiplicity of seismometers to determine a direction of propagation at the T- stations. In the course of exploring several avenues, including the study of polarization of signals recorded at the two three-component H06 (Socorro Island, Mexico) broad-band seismometers, we have also re-discovered their potential for civil application to tsunami warning.