10:45 AM - 12:15 PM
[MAG32-P03] Broadband observation of hydro-pressure associated with typhoons
The long-term DAS measurement is being conducted using an inoperable submarine cable off Muroto, Japan since 2021. The stable laser device has been attached as an incident light in 2022, making it possible to become better signal-to-noise ratio (SNR) in the low-frequency range below 0.1 Hz. Therefore, we examined the DAS dataset during typhoons approaching the submarine cable and discussed the detectability of pressure signals associated with tphoons since low-frequency signals could be excited. The dataset of the dense ocean-floor network for earthquakes and tsunamis (DONET) and offshore wave height by the nationwide ocean wave information network for ports and harbours (NOWPHAS) were available. Two typhoons passed near the mainland of Japan (Honshu) in 2022; one is Typhoon No. 14 “Nanmadol” and the other is Typhoon No. 15 “Talas” at an interval of one week. When they were passing near the submarine cable, the former “Nanmadol” was stronger (lower in barometric pressure) than the latter “Talas”. The NOWPHAS suggests the long-period swells (period ~ 10 s) became predominant gradually prior to “Nanmadol” approaching and dismiss abruptly after it passed. “Talas” also generated the swells, but the amplitude (the wave height) and the predominant period were smaller than “Nanmadol”. Corresponding to the NOWPHAS, the ocean microseismic noise (period ~ 10 s) became apparent in the DONET pressure sensors during the two typhoons passing. Additionally, energy of the infragravity wave (period ~ 100 s) is dominated in the DONET pressure sensors, whose amplitude is larger than the ocean background noise. The infragavity wave could also be identified by the DAS, on the contrary, the amplitude is smaller than the ocean microseismic noise. Since DAS is more sensitive along the cable parallel than the cable normal, further discussions may be needed to quantify the amplitude.