1933 Sanriku Earthquake and Tsunami

On March 2, 1933, at approximately 5:30PM, an 8.4 magnitude earthquake occurred about 180 miles off the Sanriku Coast, quickly traveling towards the city of Honshu, Japan (USGS). This earthquake then triggered a tsunami, which was the truly devastating blow. The tsunami produced waves which in some areas were recorded to be up to 94 feet high (USGS). The actual shocks of the earthquake only occurred at or less than 50km or 31 miles underneath the surface of the ocean (Uchida et al., 2016) Due to this earthquake/tsunami duo, there were an estimated 3,000 deaths (USGS). This tsunami not only injured or killed individuals, it also resulted in over 8,000 homes being either damaged or entirely washed away by the massive incoming waves (USGS). The tsunami had also reached part of Hawaii and caused some damage there, though the earthquake had been detected offshore and an evacuation was held, leading to minimal structural damage and no recorded deaths (Okal, Kirby and Kalligeris). The 1933 Sanriku earthquake would continue to produce aftershocks for months after the original occurrence (Fig 2.), some of them even coming in at a magnitude of 6 (Okal, Kirby and Kalligeris, 2016). This earthquake has been since been recognized as one of the largest and most devastating  natural disasters in Japan’s history (Live Science, 2011). 

Figure 1: Damages done by the 1933 Sanriku Earthquake and Tsunami. (Source: Ferreira, Leandro. “1933 Disaster Photos Are Listed as Cultural Assets,” April 25, 2019. https://en.connectionjapan.com/2019/04/25/fotos-do-desastre-de-1933-sao-listadas-como-bens-culturais/.) 

Figure 2: Map of main shock (labeled MS) and aftershocks. Graphs a and b show what were thought to be the original positions and depths of the shocks, while graphs c and d show the positions and depths of the shocks after 3-D modeling. Please reference article for more details. (Source: Naoki Uchida, Stephen H. Kirby, Norihito Umino, Ryota Hino, Tomoe Kazakami, The great 1933 Sanriku-oki earthquake: reappraisal of the main shock and its aftershocks and implications for its tsunami using regional tsunami and seismic data, Geophysical Journal International, Volume 206, Issue 3, 1 September 2016, Pages 1619–1633, https://doi.org/10.1093/gji/ggw234). 

This earthquake and tsunami duo was not the first of its kind in this area. 1896 saw a natural disaster (Fig. 3) that was just as, if not more devastating than the one which is the subject of this blog. The earlier disaster saw the death of over 25,000 individuals with a 8.5 magnitude earthquake and reported 80 feet tall waves (U.S Geological Service). It was said to have “instantly swept away all houses and people when it reach land” (U.S. Geological Survey). This tsunami too affected Hawaii, though in this case, there was much more damage done than in the case of the 1933 Sanriku earthquake (U.S. Geological Survey). When comparing these events, one can see some major differences. While the 1896 earthquake had nearly the same magnitude and smaller waves than the event in 1933, we can see that there were more reported damages in not only Japan, but also in Hawaii. This fact by itself can lead one to believe that the individuals living near the Sanriku Coast began to better prepare themselves for events like this, though things infrastructure and education. The U.S. Geological Survey even has a quote claiming that the 1896 event was what really pushed Japan to start studying events like tsunamis, which could have greatly impacted their preparedness for future events, such as the 1933 Sanriku disaster (U.S. Geological Survey). In terms of things that could have been done in order to mitigate the damages done by the 1933 Sanriku earthquake and tsunami, there are a few things on the list. One of the most important things that could have been done is to educate the public. Recognizing signs of a tsunami could be vital to having time to get to higher ground. Then comes a warning system. One of the major reasons there were no deaths in Hawaii during the tsunami in 1933 was because of the evacuation that took place since ample warning was given. Some kind of warning could have saved many individuals in Honshu and the surrounding areas. Finally is reinforcing structures. Adding reinforcements to preexisting structures could help them to not be completely destroyed during an earthquake and a sort of sea wall could have helped slightly in terms of the following tsunami. 

Figure 3: Damages done by the 1896 Sanriku Earthquake and Tsunami (source: Numata, K. (2014, March 26). Images of 1896 Sanriku quake found. The Japan Times. https://www.japantimes.co.jp/news/2014/03/26/national/history/images-of-1896-sanriku-quake-found/.)

This natural disaster greatly affected the residents of the Sanriku Coast and has left its mark on not only the history of Japan but on the geological history of the world. 

Video: This video shows footage taken after the 1933 Sanriku Earthquake and Tsunami occurred. It shows the damages done to the land and structures of Kamaishi, Japan (noise warning). 

Sources

Emile A. Okal, Stephen H. Kirby, Nikos Kalligeris, The Showa Sanriku earthquake of 1933 March 2: a global seismological reassessment, Geophysical Journal International, Volume 206, Issue 3, 1 September 2016, Pages 1492–1514, https://doi.org/10.1093/gji/ggw206

Ferreira, Leandro. “1933 Disaster Photos Are Listed as Cultural Assets,” April 25, 2019. https://en.connectionjapan.com/2019/04/25/fotos-do-desastre-de-1933-sao-listadas-como-bens-culturais/.

Live Science. “Japan's Biggest Earthquakes,” April 8, 2011. https://www.livescience.com/30312-japan-earthquakes-top-10-110408.html.

Naoki Uchida, Stephen H. Kirby, Norihito Umino, Ryota Hino, Tomoe Kazakami, The great 1933 Sanriku-oki earthquake: reappraisal of the main shock and its aftershocks and implications for its tsunami using regional tsunami and seismic data, Geophysical Journal International, Volume 206, Issue 3, 1 September 2016, Pages 1619–1633, https://doi.org/10.1093/gji/ggw234

Numata, K. (2014, March 26). Images of 1896 Sanriku quake found. The Japan Times. https://www.japantimes.co.jp/news/2014/03/26/national/history/images-of-1896-sanriku-quake-found/. 

U.S. Geological Survey. Today in Earthquake History. U.S. Geological Survey. https://earthquake.usgs.gov/learn/today/index.php?month=6.  

USGS “M 8.4 - 1933 Sanriku (Sanriku-Oki) Earthquake, Japan.” USGS Earthquake Hazards Program. USGS. https://earthquake.usgs.gov/earthquakes/eventpage/official19330302173100_30/impact