2016 年 72 巻 2 号 p. I_337-I_342
The hydrophone triplets of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System (IMS) hydroacoustic (HA) network have been installed in the water-column at different locations around the world's oceans since the early 2000s. The present study focuses on hydrophone data recorded at the IMS hydroacoustic station HA11 Wake Island during the 2011 Tohoku earthquake, with the purpose of estimating the directivity of T-phase signals and identifying tsunami warning indicators. In the first part of the paper, IMS hydrophone data not including contributions from tsunami stages are analyzed with the objective of detecting the T-phase and determining its direction of arrival (DOA). The second part of the study addresses the detectability of pressure variations associated with the tsunami itself. For the analysis of T-phase signal directivity, a three-step process is introduced to obtain a signal envelope associated with the T-phase which makes it possible to apply F-K analysis without spatial aliasing. It is shown that using the three-step envelope processing technique, the direction of the T-phase signals acquired at the IMS hydrophone triplets can be accurately estimated. For the analysis of tsunami detectability, it is shown that short period dispersive tsunami signals can be identified by IMS hydrophone triplets.