Ten years ago today, a 9.1 magnitude earthquake struck off the northeastern coast of Honshu on the Japan Trench, a subduction zone. Subduction occurs when an oceanic plate dives under another plate. The activity generated a devastating tsunami, which reached Japan within 30 minutes. It was the largest magnitude earthquake ever recorded in the region, and was the third-largest in the world since 1900.
The tsunami affected a 1,242-mile stretch of Japan’s Pacific coast, and the waves reached almost 130 feet in some places as they slammed into the Iwate Prefecture. The devastation resulting from this Tohoku Earthquake and Tsunami event, often referred to as the Great East Japan earthquake and tsunami, not only caused an estimated $220 billion USD worth of damages (the most expensive natural disaster in history), but also more than 18,000 deaths, including several thousand victims who were never recovered.
Additionally, the tsunami disabled the power supply and cooling systems of three Fukushima Daiichi nuclear reactors, where all three cores largely melted within the first three days. The accident was rated level 7 (major accident) on the International Nuclear and Radiological Event Scale, due to high radioactive releases over days 4 to 6. The image below, captured via the Defense Meteorological Satellite Program (DMSP) satellite, shows an average nighttime view of Japan, followed by a view showing the decrease in nighttime lights due to power outages after the event.
The animation above shows wave height in centimeters, the scale of which ranges from 0 to 240+ centimeters, (or 0 to 94+ inches), as the tsunami propagated. Darker blue, purple, gray, and black represent the highest amplitudes. This imagery helps show the far-reaching effects of this event throughout the Pacific.
According to satellite altimetry expert Walter H. F. Smith, there are several bits of information that came together to make this visual. With NOAA's tsunami observing system, a set of bottom pressure gauges can feel a tsunami and measure its height. They relay that information to a buoy floating on the ocean surface, which in turn relays it through satellites to the NOAA data system on land. They are called DART buoys.
The primary map image is known as a MOST (Method of Splitting Tsunami) map, which was also generated by the NOAA Pacific Marine Environmental Laboratory (PMEL). Smith adds, “They run a computer simulation of what the tsunami heights might have been around the world, as a function of time, and they produce movies visualizing that. But they do not do it in real time, because they get the info later and the computing resources required are huge.”
For some events, such as the 2004 Boxing Day Tsunami in the Indian Ocean, the satellite altimeters used to measure sea level from space just happened to be passing over the Indian Ocean at the right time to measure the tsunami. With Fukushima in 2011, the satellites didn’t see much of interest the day of the event. The MOST data collected after the tsunami, however, provided much more information.
NOAA operates two tsunami warning centers. The National Tsunami Warning Center serves the continental United States, Alaska, and Canada, while the Pacific Tsunami Warning Center serves the Hawaiian Islands, the U.S. Pacific and Caribbean territories and the British Virgin Islands, and is the primary international forecast center for the Pacific and Caribbean.