[H-CG21] Monitoring the Comprehensive Nuclear-Test-Ban Treaty: Status, operations, and scientific application

[HCG21-P01] IMS and fiber optic detection of hydroacoustic signals originating from a series of submarine earthquakes in Izu-Ogasawara Islands, Japan

*Hiroyuki Matsumoto¹, Mario Zampolli², Eiichiro Araki¹, Georgios Haralabus², Takashi Yokobiki¹ (1.Japan Agency for Marine-Earth Science and Technology, 2.Comprehensive Nuclear-Test-Ban Treaty Organization)

On 8 October, 2023, a series of submarine earthquakes that took place in Izu-Ogasawara Islands, Japan, excited at least 14 hydroacoustic waves (i.e., T-waves or H-waves) for a period of three hours. These signals were detected by the CTBT International Monitoring System (IMS) hydrophone triplets station HA11 at Wake Island.Although the intensity among packets varied, the frequency contents were commonly broadband, suggesting that explosive phenomena occurred during this series of episodic events. We performed cross-correlation analysis to determine the direction of arrival (DOA) of the hydroacoustic waves and make hypotheses about their origin. The north triplet shows that the DOA of hydroacoustic signals were pointing slightly southward Sofugan Island. On the other hand, the south triplet shows that the DOA of the hydroacoustic signals were determined Torishima Island and Sofugan Island. Overall, our analysis suggests that the hydroacoustic sources were located near Sofugan Island. The same signals were also detected by an arbitrary channel on DAS using a fiber optic submarine cable off Shikoku Island at the opposite direction to HA11. The frequency contents observed by DAS were very similar to those at HA11 hydrophone triplets, supporting the detection capability of hydroacoustic signals by DAS.