1:45 PM - 2:00 PM
[HDS10-06] Distinct characteristics between the leading and following tsunamis from the 2022 Tonga eruption observed at coastal and deep sea areas near Japan and in the Pacific
Keywords:ocean bottom tsunami sensors, air waves recorded by barograms, 2022 Tonga eruption tsunami, Ocean atmosphere coupled tsunami
The Lamb pressure pulse propagated from the 2022 Tonga eruption was also observed at the deep ocean tsunamimeters in the Pacific. The propagation speed determined from the 10 DART buoys that recorded the impulsive leading pressure pulse is 298 m/s that coincides with the Lamb wave propagation speed. The propagation speeds vary among stations. The speed is much faster than the usual tsunami propagation speed determined by the local bathymetry. The estimated origin time of the peak is within 1 min from 4:30 UT.
A peculiar feature of the pressure pulse observed at deep ocean is that the amplitude is much larger than the subaerial pressure pulse, about two times or more. A few stations out of 10 exceed 6 hPa. On land outside Tonga the maximum observed peak amplitude does not exceed 6 hPa. The average of the peak amplitude of the 10 stations is more than 4 hPa. The dynamic response to the fast-spreading pressure pulse along the ocean surface likely caused this excess pressure impulse in the deep ocean bottom. The deep ocean pressure records are especially useful for filling the large observational coverage gap in the ocean. To utilize the tsunami records we need to understand the mechanism of the pressure increase and establish a method to retrieve a subaerial pressure.
The leading impulsive tsunami as well as the following tsunami reached near Japan and recorded deep ocean tsunami network S-net and numerous coastal tide gauges. We found that not the leading pressure pulse but the following tsunami observed at the deep ocean mainly contributed to the largest sea level change at coasts.
The ocean bottom pressure starts with an impulsive pressure with the maximum amplitude of about 5 hPa, as we found in the Pacific, and the pressure pulse shape is similar to the barograms on land with the maximum amplitude of about 2 hPa. Here we confirmed the pressure amplification at the deep ocean by direct observation. As the Lamb wave pulse goes over the tide gauge but it does not immediately respond to the pressure peak. After the pressure peak passes the tide level slowly and gradually grows. An interesting observational point is that the sea-level keeps oscillatory increasing up to 2 to 6 hours after the passage of the pressure pulse and the peak sea-level amplitude is about 1m. We need to investigate the two mechanisms. The first is why the leading pressure pulse recorded in the ocean bottom does not directly damage the coastal area. It seems magically disappeared. The second is why the delayed increase of tide level occurs at the coasts.
A peculiar feature of the pressure pulse observed at deep ocean is that the amplitude is much larger than the subaerial pressure pulse, about two times or more. A few stations out of 10 exceed 6 hPa. On land outside Tonga the maximum observed peak amplitude does not exceed 6 hPa. The average of the peak amplitude of the 10 stations is more than 4 hPa. The dynamic response to the fast-spreading pressure pulse along the ocean surface likely caused this excess pressure impulse in the deep ocean bottom. The deep ocean pressure records are especially useful for filling the large observational coverage gap in the ocean. To utilize the tsunami records we need to understand the mechanism of the pressure increase and establish a method to retrieve a subaerial pressure.
The leading impulsive tsunami as well as the following tsunami reached near Japan and recorded deep ocean tsunami network S-net and numerous coastal tide gauges. We found that not the leading pressure pulse but the following tsunami observed at the deep ocean mainly contributed to the largest sea level change at coasts.
The ocean bottom pressure starts with an impulsive pressure with the maximum amplitude of about 5 hPa, as we found in the Pacific, and the pressure pulse shape is similar to the barograms on land with the maximum amplitude of about 2 hPa. Here we confirmed the pressure amplification at the deep ocean by direct observation. As the Lamb wave pulse goes over the tide gauge but it does not immediately respond to the pressure peak. After the pressure peak passes the tide level slowly and gradually grows. An interesting observational point is that the sea-level keeps oscillatory increasing up to 2 to 6 hours after the passage of the pressure pulse and the peak sea-level amplitude is about 1m. We need to investigate the two mechanisms. The first is why the leading pressure pulse recorded in the ocean bottom does not directly damage the coastal area. It seems magically disappeared. The second is why the delayed increase of tide level occurs at the coasts.