Currently, a fixed set-up is needed to identify and confirm that an earthquake has created a tsunami. As a tsunami rolls through the ocean, a sensor at the ocean floor will register slight changes in the water density. Should a threshold be met or exceeded, a signal is then sent to a floating buoy, transmitted to a satellite, and finally downloaded by warning scientists. It’s a physical process that requires a tsunami to actually flow over a sensor. Keep in mind that most tsunamis are created from earthquakes, but not all earthquakes create a tsunami. Conversely, a tsunami warning is usually issued after strong earthquakes even if one isn’t confirmed. This process lends itself to multiple warnings being issued even if there is not an immediate threat. In turn, the public can lose faith in the warning system altogether (always crying wolf).
Identifying and confirming tsunamis is important because it helps to eliminate false warnings. At our current state a tsunami has to impact land or roll over one of these units for it to be confirmed/identified and can take several hours. Presently, there are roughly only 70 observations stations for the miles of ocean we would need to monitor for this threat. With the limited resources, it is very tough to observe a tsunami in a timely fashion let alone broadcast its corresponding characteristics.
One interesting note is that a tsunami warning was issued for parts of Alaska a day before the 9.0 earthquake that struck Japan 24 hours later. This Alaskan tsunami warning was issued because of a weaker earthquake that did not produce a tsunami. Due to the eventual earthquake on Friday, the earthquake on Thursday was then defined as a “foreshock”.
As mentioned in the video, the atmosphere is now being researched to help identify tsunamis. Not only will a tsunami have a fast (500 mph +) horizontal speed, but recent GPS data has indicated a tsunami will also produce slight perturbations upwards, vertically into the atmosphere. The vertical waves originate at the sea surface, but are being tracked and located in our ionosphere. In total, the atmosphere waves reach the ionosphere in about 15 minutes and in turn can dramatically change the watch/warning time we currently rely on. Further calculations with this data can help confirm a tsunami, the speed it is moving, and the overall height or strength it is carrying.
It’s some really interesting technology that will hopefully find a home in our watch/warning system. If you would like to read more, I’ve linked one of the sources I used when putting this week’s World of Weather together.
Giovanni Occhipinti, Attila Komjathy, Philippe Lognonné